CPSC 441: Review (W06)
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Transcript of CPSC 441: Review (W06)
CPSC 441 Review 1
CPSC 441 Review (W06)
Instructor Dr Anirban MahantiOffice ICT 745Email mahanticpscucalgarycaDate April 12 2006
Text BookldquoComputer Networking A Top Down Approach
Featuring the Internetrdquo 3rd edition Jim Kurose and Keith Ross Addison-Wesley 2005
CPSC 441 Review 2
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 3
Reference Models
OSI model 7-layer model application presentation session transport network data link and physical
TCPIP model 4-layers application transport Internet and Host-to-Network
Internet Protocol Stack ndash a hybrid of TCPIP and OSI reference models
CPSC 441 Review 4
Layers and Protocols
Layered network architecture hellip why Reduces design complexity
The purpose of a layer Layer-N peers converse with each other
using protocols each layer provides functionality to the a higher layer
Protocols A set of rules governing the format and
meaning of messages exchanges by peer entities within a layer
CPSC 441 Review 5
Protocols Layers and PDUrsquos
Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 6
More on Layers and Protocols
Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 7
Internetworks
A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork
Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc
CPSC 441 Review 8
Network Core
Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks
Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA
Circuit vs Message vs Packet Switching
CPSC 441 Review 9
DelayLoss in Packet Switched Networks
Queuing delay and packet loss
Transmission delay
Propagation delay
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 2
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 3
Reference Models
OSI model 7-layer model application presentation session transport network data link and physical
TCPIP model 4-layers application transport Internet and Host-to-Network
Internet Protocol Stack ndash a hybrid of TCPIP and OSI reference models
CPSC 441 Review 4
Layers and Protocols
Layered network architecture hellip why Reduces design complexity
The purpose of a layer Layer-N peers converse with each other
using protocols each layer provides functionality to the a higher layer
Protocols A set of rules governing the format and
meaning of messages exchanges by peer entities within a layer
CPSC 441 Review 5
Protocols Layers and PDUrsquos
Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 6
More on Layers and Protocols
Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 7
Internetworks
A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork
Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc
CPSC 441 Review 8
Network Core
Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks
Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA
Circuit vs Message vs Packet Switching
CPSC 441 Review 9
DelayLoss in Packet Switched Networks
Queuing delay and packet loss
Transmission delay
Propagation delay
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 3
Reference Models
OSI model 7-layer model application presentation session transport network data link and physical
TCPIP model 4-layers application transport Internet and Host-to-Network
Internet Protocol Stack ndash a hybrid of TCPIP and OSI reference models
CPSC 441 Review 4
Layers and Protocols
Layered network architecture hellip why Reduces design complexity
The purpose of a layer Layer-N peers converse with each other
using protocols each layer provides functionality to the a higher layer
Protocols A set of rules governing the format and
meaning of messages exchanges by peer entities within a layer
CPSC 441 Review 5
Protocols Layers and PDUrsquos
Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 6
More on Layers and Protocols
Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 7
Internetworks
A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork
Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc
CPSC 441 Review 8
Network Core
Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks
Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA
Circuit vs Message vs Packet Switching
CPSC 441 Review 9
DelayLoss in Packet Switched Networks
Queuing delay and packet loss
Transmission delay
Propagation delay
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 4
Layers and Protocols
Layered network architecture hellip why Reduces design complexity
The purpose of a layer Layer-N peers converse with each other
using protocols each layer provides functionality to the a higher layer
Protocols A set of rules governing the format and
meaning of messages exchanges by peer entities within a layer
CPSC 441 Review 5
Protocols Layers and PDUrsquos
Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 6
More on Layers and Protocols
Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 7
Internetworks
A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork
Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc
CPSC 441 Review 8
Network Core
Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks
Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA
Circuit vs Message vs Packet Switching
CPSC 441 Review 9
DelayLoss in Packet Switched Networks
Queuing delay and packet loss
Transmission delay
Propagation delay
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 5
Protocols Layers and PDUrsquos
Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 6
More on Layers and Protocols
Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 7
Internetworks
A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork
Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc
CPSC 441 Review 8
Network Core
Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks
Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA
Circuit vs Message vs Packet Switching
CPSC 441 Review 9
DelayLoss in Packet Switched Networks
Queuing delay and packet loss
Transmission delay
Propagation delay
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 6
More on Layers and Protocols
Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211
Assuming the Internet Protocol Stack
CPSC 441 Review 7
Internetworks
A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork
Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc
CPSC 441 Review 8
Network Core
Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks
Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA
Circuit vs Message vs Packet Switching
CPSC 441 Review 9
DelayLoss in Packet Switched Networks
Queuing delay and packet loss
Transmission delay
Propagation delay
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 7
Internetworks
A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork
Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc
CPSC 441 Review 8
Network Core
Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks
Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA
Circuit vs Message vs Packet Switching
CPSC 441 Review 9
DelayLoss in Packet Switched Networks
Queuing delay and packet loss
Transmission delay
Propagation delay
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 8
Network Core
Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks
Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA
Circuit vs Message vs Packet Switching
CPSC 441 Review 9
DelayLoss in Packet Switched Networks
Queuing delay and packet loss
Transmission delay
Propagation delay
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 9
DelayLoss in Packet Switched Networks
Queuing delay and packet loss
Transmission delay
Propagation delay
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 10
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 11
Application Layer
Processes communicating across networks
What is HTTP Hypertext Transfer Protocol ndash the Webrsquos
application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is
encountered Persistent ndash multiple objects can be sent
over a single TCP connection between the server and the client
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 12
HTTP Continued hellip
HTTP headers How is the end of an object determined in
HTTP11 HTTP methods
GET HEAD POST PUT hellip HTTP response codes
1xx 2xx 3xx 4xx 5xx
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 13
The World Wide Web
What is a Web Proxy What is a caching hierarchy Caching issues ndash
Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request
Cache replacement issues Prefetching
Cookies ndash a means to maintain state in stateless HTTP servers
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 14
DNS Domain Name System
Internet hosts IP address (32 bit) - used for addressing
datagrams ldquonamerdquo eg wwyahoocom - used by
humans
DNS provides translation between host name and IP address distributed database implemented in
hierarchy of many name servers Distributed for scalability amp reliability
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 15
DNS Services
Hostname to IP address translation Host aliasing
Canonical and alias names Mail server aliasing Load distribution
Replicated Web servers set of IP addresses for one canonical name
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 16
requesting hostcispolyedu
gaiacsumassedu
root DNS server
local DNS serverdnspolyedu
1
23
4
5
6
authoritative DNS serverdnscsumassedu
78
TLD DNS server
DNS Infrastructure
Host at cispolyedu wants IP address for gaiacsumassedu
Infrastructure Client resolver Local DNS server Authoritative DNS
Server Root DNS Server Top-Level Domain
DNS Server
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 17
Electronic Mail
Three major components
user agents eg Eudora Outlook
Pine Netscape Messenger
mail servers Incoming outgoing
messages Push protocol ndashSMTP
Pull protocol ndash HTTP IMAP POP3
user mailbox
outgoing message queue
mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
SMTP
SMTP
SMTP
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 18
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 19
Transport Layer
Logical end-to-end communication between processes running on different end systems
Multiplexingde-multiplexing Service models UDP vs TCP
UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow
control congestion control and reliable data delivery
Some applications use UDP while some use TCP Why
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 20
Reliable Delivery Concepts
GBN SR ndash also called ldquostop-and-waitrdquo protocols
ACK NAK SACK Performance of ldquostop-and-waitrdquo
Pipelining Similaritydifferences between TCP and
the above protocols
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 21
TCP segment structure (12)
source port dest port
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG urgent data (generally not used)
ACK ACK valid
PSH push data now(generally not used)
RST SYN FINconnection estab(setup teardown
commands)
bytes rcvr willingto accept
countingby bytes of data(not segments)
Internetchecksum
(as in UDP)
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 22
TCP Segment Structure (22)
Sequence and acknowledgement numbering
TTL Checksum ndash compulsory in TCP but not
in UDP Handshaking procedures during TCP
connection set-up and connection termination SYN FIN RST fields
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 23
TCP Flow Control
receive side of TCP connection has a receive buffer
speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be
slow at reading from buffer
sender wonrsquot overflow
receiverrsquos buffer bytransmitting too
much too fast
flow control
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 24
TCP Connection Establishment
client
SYN seq=x
server
SYN+ACK seq=y ack=x+1
ACK ack=y+1
CLOSED
LISTEN
SYN_SENTSYN_RCVD
Established
Passive open
SYNSYN+ACK
ACK
Active openSYN
SYN+ACKACK
Solid line for client
Dashed line for server
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 25
TCP Connection Termination
client
FIN
server
ACK
ACK
FIN
closing
tim
ed w
ait
FIN_WAIT1
FIN_WAIT2
CLOSE_WAIT
LAST_ACK
CLOSED
TIME_WAIT
CLOSED
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 26
Principles of Congestion Control Congestion informally ldquotoo many sources
sending too much data too fast for network to handlerdquo
Different from flow control Manifestations
Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router
buffers) Results in unfairness and poor utilization of
network resources Resources used by dropped packets (before they
were lost) Retransmissions Poor resource allocation at high load
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 27
Congestion Control Approaches Goal Throttle senders as needed to ensure
load on the network is ldquoreasonablerdquoEnd-end congestion control
no explicit feedback from network congestion inferred from end-system
observed loss delay approach taken by TCP
Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 28
TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the
network to window W Roughly
W is dynamic function of perceived network congestion
rate = W
RTT Bytessec
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 29
TCP Congestion Controls Tahoe (Jacobson 1988)
Slow Start Congestion Avoidance Fast Retransmit
Reno (Jacobson 1990) Fast Recovery
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 30
TCP Tahoe Basic ideas
Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time
estimation error recoveryfor every ACK
if (W lt ssthresh) then W++ (SS) else W += 1W (CA)
for every loss
ssthresh = W2 W = 1
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 31
TCP Reno Fast Recovery Objective prevent `pipersquo from emptying
after fast retransmit each dup ACK represents a packet having
left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)
W ssthresh (window deflation)enter CA mode
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 32
TCP Reno Summary
Fast Recovery along with Fast Retransmit used to avoid slow start
On 3 duplicate ACKs Fast retransmit and fast recovery
On timeout Fast retransmit and slow start
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 33
TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate
What happens if L-gt0 Does link capacity matter if we
experience random loss High-speed TCP
LRTT
MSS221
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 34
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 35
Network Layer
Transport segment from sending to receiving host
Network layer protocols in every host router [contrast with transportapplication layer]
Main functions of network layer Forwarding ndash moving datagrams within a
router Routing ndash determine end-to-end paths taken
by packets
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 36
IP datagram format
ver length
32 bits
data (variable lengthtypically a TCP
or UDP segment)
16-bit identifier
Internet checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentationreassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
headlen
type ofservice
ldquotyperdquo of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) Eg timestamprecord routetaken specifylist of routers to visit
how much overhead with TCP
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 37
IPv4 Addressing IP address 32-bit
identifier for host router interface
interface connection between hostrouter and physical link routerrsquos typically have
multiple interfaces host may have
multiple interfaces IP addresses
associated with each interface
223111
223112
223113
223114 223129
223122
223121
223132223131
2231327
223111 = 11011111 00000001 00000001 00000001
223 1 11
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 38
Classful Addressing
Addresses consists of Network part Host part
IP addresses divided into five classes A B C D and E
Problems
0Network (7 bits)
Host (24 bits)
1 Network(14 bits)
Host (16bits)
0
1110 Multicast address
Class A
Class D
Class B
110 Network(21 bits)
Host (8bits)
Class C
1111 Future use addresses
Class E
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 39
Subnets Motivation
The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts
needs a class B address Class B addresses can get exhausted before we have 4 billion hosts
Take bits from the host number part to create a ldquosubnetrdquo number
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 40
Addressing in the Internet
CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in
subnet portion of address Before CIDR Internet used a class-based
addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp
11001000 00010111 00010000 00000000
subnetpart
hostpart
2002316023
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 41
NAT Network Address Translation
10001
10002
10003
10004
13876297
local network(eg home network)
100024
rest ofInternet
Datagrams with source or destination in this networkhave 100024 address for
source destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address 13876297different source port numbers
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 42
Routing Algorithm Classification
1 Global decentralized
Global all routers have complete
topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about
physically-connected neighbors
Iterative distributed computations
ldquodistance vectorrdquo algorithms
2 Static dynamicStatic routes change slowly
over time
Dynamic routes change more
quickly periodic update in response to link
cost changes
3 Load sensitivity Many Internet routing
algos are load insensitive
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 43
Why Hierarchical Routing scale with 200 million destinations
canrsquot store all destrsquos in routing tables routing table exchange would swamp links
administrative autonomy internet = network of networks each network admin may want to control routing in
its own network
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 44
Hierarchical Routing
aggregate routers into regions ldquoautonomous systemsrdquo (AS)
routers in same AS run same routing protocol ldquointra-ASrdquo routing
protocol routers in different AS
can run different intra-AS routing protocol
Gateway router Direct link to router
in another AS Establishes a
ldquopeeringrdquo relationship
Peers run an ldquointer-AS routingrdquo protocol
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 45
3b
1d
3a
1c2aAS3
AS1
AS21a
2c2b
1b
Intra-ASRouting algorithm
Inter-ASRouting algorithm
Forwardingtable
3c
Interconnected ASes
Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries
for internal dests Inter-AS amp Intra-As
sets entries for external dests
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 46
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 47
Link Layer IntroductionSome terminology hosts and routers are nodes communication channels
that connect adjacent nodes along communication path are links wired links wireless links LANs
layer-2 packet is a frame encapsulates datagram
ldquolinkrdquo
data-link layer has responsibility of transferring datagram from one node to adjacent node over a link
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 48
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
Question how to determineMAC address of Bknowing Brsquos IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 49
Multiple Access Links and Protocols
Two types of ldquolinksrdquo point-to-point
PPP for dial-up access point-to-point link between Ethernet switch and host
broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 50
Taxonomy of Multiple Access Control Protocols
Three broad classes Channel Partitioning
divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)
allocate piece to node for exclusive use Random Access
channel not divided allow collisions ldquorecoverrdquo from collisions
ldquoTaking turnsrdquo Nodes take turns but nodes with more to
send can take longer turns
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 51
Random Access Protocols
When node has packet to send transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies
how to detect collisions how to recover from collisions (eg via delayed
retransmissions)
Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 52
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 53
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 54
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load heavy load random wait
will be longer first collision choose K
from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 55
CSMACD efficiency tprop = max prop between 2 nodes in LAN
ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0
Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap
transprop tt 51
1efficiency
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 56
Switches Routers and Hubs Hubs are physical layer repeaters
no CSMACD at hub
Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning
algos
Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 57
A network with switch router and hubs
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 58
Wireless Networking Technologies Mobile devices ndash laptop PDA cellular
phone wearable computer hellip
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100
meters)
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 59
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff mobile changes base station providing connection into wired network
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 60
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network route among themselves
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 61
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access)
AB
C
Hidden terminal problem B A hear each other B C hear each other A C can not hear each
othermeans A C unaware of their
interference at B
A B C
Arsquos signalstrength
space
Crsquos signalstrength
Signal fading B A hear each other B C hear each other A C can not hear each other
interfering at B
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 62
IEEE 80211 MAC Protocol CSMACA
80211 sender1 if sense channel idle for DIFS then
transmit entire frame (no CD)2 if sense channel busy then
start random backoff timetimer counts down while channel idletransmit when timer expires
3 if no ACK increase random backoff interval repeat 2
80211 receiver- if frame received OK
return ACK after SIFS (ACK needed due to hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 63
Avoiding collisions (more)
idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore
short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes
sender transmits data frame other stations defer transmissions
Avoid data frame collisions completely using small reservation packets
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 64
Collision Avoidance RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 65
Mobile IP Overview
Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it indirect routing communication from
correspondent to mobile goes through home agent then forwarded to remote
direct routing correspondent gets foreign address of mobile sends directly to mobile
not scalable
to millions of mobiles
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 66
Outline Introduction
Applications
Transport Layer
Network Layer
LANs and WLANs
Multimedia Networking
Questions
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 67
MM Networking Applications Fundamental
characteristics Typically delay
sensitive end-to-end delay delay jitter
But loss tolerant infrequent losses cause minor glitches
Antithesis of data
Classes of MM applications
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 68
Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay
loss
Todayrsquos multimedia applications implement functionality at the app layer to mitigate
(as best possible) effects of delay loss
But you said multimedia apps requiresQoS and level of performance to be
effective
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 69
How to provide better support for Multimedia (14)
Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows
Fundamental changes in Internet so that apps can reserve end-to-end bandwidth
Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 70
Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with
large number of flows Flexible Service Models Intserv has only two classes Desire
ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class
Diffserv approach simple functions in network core relatively complex functions at
edge routers (or hosts) Donrsquot define define service classes provide functional components
to build service classes
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 71
How to provide better support for Multimedia (34) Challenging to stream large
files (eg video) from single origin server in real time
Solution replicate content at hundreds of servers throughout Internet content downloaded to
CDN servers ahead of time
placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths
CDN server typically in edgeaccess network
origin server in North America
CDN distribution node
CDN serverin S America CDN server
in Europe
CDN serverin Asia
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 72
How to provide better support for Multimedia (44)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicatecreationtransmissionduplicate
duplicate
Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication
MulticastBroadcast
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 73
Finally hellip Examination Format Technical Terms ndash provide technical
terms that best fit a given definition Eg A field in IPv4 that provides for error
detection ndash Checksum Some short answer questions
Eg Compare and contrast datagram networks and virtual circuit networks
You need to only write main points Answer should be as brief as possible
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-
CPSC 441 Review 74
Good Luck and Questions hellip
- CPSC 441 Review (W06)
- Outline
- Reference Models
- Layers and Protocols
- Protocols Layers and PDUrsquos
- More on Layers and Protocols
- Internetworks
- Network Core
- DelayLoss in Packet Switched Networks
- Slide 10
- Application Layer
- HTTP Continued hellip
- The World Wide Web
- DNS Domain Name System
- DNS Services
- DNS Infrastructure
- Electronic Mail
- Slide 18
- Transport Layer
- Reliable Delivery Concepts
- TCP segment structure (12)
- TCP Segment Structure (22)
- TCP Flow Control
- TCP Connection Establishment
- TCP Connection Termination
- Principles of Congestion Control
- Congestion Control Approaches
- TCP Congestion Control Overview
- TCP Congestion Controls
- TCP Tahoe
- TCP Reno Fast Recovery
- TCP Reno Summary
- TCP Reno Throughput
- Slide 34
- Network Layer
- IP datagram format
- IPv4 Addressing
- Classful Addressing
- Subnets Motivation
- Addressing in the Internet
- NAT Network Address Translation
- Routing Algorithm Classification
- Why Hierarchical Routing
- Hierarchical Routing
- Interconnected ASes
- Slide 46
- Link Layer Introduction
- ARP Address Resolution Protocol
- Multiple Access Links and Protocols
- Taxonomy of Multiple Access Control Protocols
- Random Access Protocols
- CSMACD (Collision Detection)
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- Switches Routers and Hubs
- A network with switch router and hubs
- Wireless Networking Technologies
- Infrastructure Mode
- Ad hoc Mode
- Wireless Network Characteristics
- IEEE 80211 MAC Protocol CSMACA
- Avoiding collisions (more)
- Collision Avoidance RTS-CTS exchange
- Mobile IP Overview
- Slide 66
- MM Networking Applications
- Multimedia Over ldquoBest Effortrdquo Internet
- How to provide better support for Multimedia (14)
- Concerns with Intserv (24)
- How to provide better support for Multimedia (34)
- How to provide better support for Multimedia (44)
- Finally hellip Examination Format
- Good Luck and Questions hellip
-