1 CSCD 439/539 Wireless Networks and Security Lecture 2 Ethernet and 802.11 Fall 2007 Some Material...
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Transcript of 1 CSCD 439/539 Wireless Networks and Security Lecture 2 Ethernet and 802.11 Fall 2007 Some Material...
1
CSCD 439539Wireless Networks and Security
Lecture 2Ethernet and 80211
Fall 2007
Some Material in these slides from JF Kurose and KW RossAll material copyright 1996-2007
2
Introduction
bull Study the OSI model
bull Focus lower two layers Link and Physical
bull Review how Ethernet is implemented ndash Will help better understand 80211 and how it
differs from wired
bull Begin to talk about 80211
3
OSI Model and Protocol Layering
bull Late 1970rsquos ndash International Organization for Standards (ISO) released a proposal for a network modelndash OSI Reference Model
bull Open Systems Interconnectionndash Based on protocol layeringndash Each layer has small defined jobndash Together layers called protocol stackndash Original OSI model includes 7 layers
4
OSI Model and Protocol Layering
bull Layer 7 ndash Application Layerbull Actual applications that use the communication
channel
bull Layer 6 ndash Presentation Layerbull How data elements are represented for
transmission ndash order of bits and bytes in numbers
bull Layer 5 ndash Session Layerbull Coordinates sessions between machines ndash helping
to initiate and manage them
5
OSI Model and Protocol Layering
bull Layer 4 ndash Transport Layerbull Reliable communication stream between two
systems
bull Layer 3 ndash Network Layerbull Responsible for moving data from one system
through routers to destination system
bull Layer 2 ndash Data Link Layerbull Moves data across one hop of the network
bull Layer 1 ndash Physical Layerbull Transmits bits over physical medium ndash copper
fiber radio link or any other medium
6
Current Internet Model
bull Current Internet maps to bottom 5 layers of the OSI modelndash Wraps the top 3 layers into application layerndash Everything above transport layer is application
responsibilityndash Looks like this hellip
7
Current Internet Modelbull Hybrid OSI Architecture
ndash Combines TCPIP standards at layers 3-5 withndash OSI standards at layers 1-2
OSI Hybrid TCPIP-OSI
Application
Presentation
Session
Application
Transport Transport
Network Internet
Data Link Data Link
Physical Physical
TCP
IP
8
Data Link and Physical
bull IEEE 802 specs focus on lower two layers of OSI modelndash Incorporate both physical and link
componentsndash All 802 networks have both a MAC (Media
Access Control) and a physical (PHY) component
9
Data Link Layer
bull Review data link layer specifics including Ethernetndash Protocol defines packet format typically called
frames where each frame encapsulates one packet from network layer
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
2
Introduction
bull Study the OSI model
bull Focus lower two layers Link and Physical
bull Review how Ethernet is implemented ndash Will help better understand 80211 and how it
differs from wired
bull Begin to talk about 80211
3
OSI Model and Protocol Layering
bull Late 1970rsquos ndash International Organization for Standards (ISO) released a proposal for a network modelndash OSI Reference Model
bull Open Systems Interconnectionndash Based on protocol layeringndash Each layer has small defined jobndash Together layers called protocol stackndash Original OSI model includes 7 layers
4
OSI Model and Protocol Layering
bull Layer 7 ndash Application Layerbull Actual applications that use the communication
channel
bull Layer 6 ndash Presentation Layerbull How data elements are represented for
transmission ndash order of bits and bytes in numbers
bull Layer 5 ndash Session Layerbull Coordinates sessions between machines ndash helping
to initiate and manage them
5
OSI Model and Protocol Layering
bull Layer 4 ndash Transport Layerbull Reliable communication stream between two
systems
bull Layer 3 ndash Network Layerbull Responsible for moving data from one system
through routers to destination system
bull Layer 2 ndash Data Link Layerbull Moves data across one hop of the network
bull Layer 1 ndash Physical Layerbull Transmits bits over physical medium ndash copper
fiber radio link or any other medium
6
Current Internet Model
bull Current Internet maps to bottom 5 layers of the OSI modelndash Wraps the top 3 layers into application layerndash Everything above transport layer is application
responsibilityndash Looks like this hellip
7
Current Internet Modelbull Hybrid OSI Architecture
ndash Combines TCPIP standards at layers 3-5 withndash OSI standards at layers 1-2
OSI Hybrid TCPIP-OSI
Application
Presentation
Session
Application
Transport Transport
Network Internet
Data Link Data Link
Physical Physical
TCP
IP
8
Data Link and Physical
bull IEEE 802 specs focus on lower two layers of OSI modelndash Incorporate both physical and link
componentsndash All 802 networks have both a MAC (Media
Access Control) and a physical (PHY) component
9
Data Link Layer
bull Review data link layer specifics including Ethernetndash Protocol defines packet format typically called
frames where each frame encapsulates one packet from network layer
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
3
OSI Model and Protocol Layering
bull Late 1970rsquos ndash International Organization for Standards (ISO) released a proposal for a network modelndash OSI Reference Model
bull Open Systems Interconnectionndash Based on protocol layeringndash Each layer has small defined jobndash Together layers called protocol stackndash Original OSI model includes 7 layers
4
OSI Model and Protocol Layering
bull Layer 7 ndash Application Layerbull Actual applications that use the communication
channel
bull Layer 6 ndash Presentation Layerbull How data elements are represented for
transmission ndash order of bits and bytes in numbers
bull Layer 5 ndash Session Layerbull Coordinates sessions between machines ndash helping
to initiate and manage them
5
OSI Model and Protocol Layering
bull Layer 4 ndash Transport Layerbull Reliable communication stream between two
systems
bull Layer 3 ndash Network Layerbull Responsible for moving data from one system
through routers to destination system
bull Layer 2 ndash Data Link Layerbull Moves data across one hop of the network
bull Layer 1 ndash Physical Layerbull Transmits bits over physical medium ndash copper
fiber radio link or any other medium
6
Current Internet Model
bull Current Internet maps to bottom 5 layers of the OSI modelndash Wraps the top 3 layers into application layerndash Everything above transport layer is application
responsibilityndash Looks like this hellip
7
Current Internet Modelbull Hybrid OSI Architecture
ndash Combines TCPIP standards at layers 3-5 withndash OSI standards at layers 1-2
OSI Hybrid TCPIP-OSI
Application
Presentation
Session
Application
Transport Transport
Network Internet
Data Link Data Link
Physical Physical
TCP
IP
8
Data Link and Physical
bull IEEE 802 specs focus on lower two layers of OSI modelndash Incorporate both physical and link
componentsndash All 802 networks have both a MAC (Media
Access Control) and a physical (PHY) component
9
Data Link Layer
bull Review data link layer specifics including Ethernetndash Protocol defines packet format typically called
frames where each frame encapsulates one packet from network layer
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
4
OSI Model and Protocol Layering
bull Layer 7 ndash Application Layerbull Actual applications that use the communication
channel
bull Layer 6 ndash Presentation Layerbull How data elements are represented for
transmission ndash order of bits and bytes in numbers
bull Layer 5 ndash Session Layerbull Coordinates sessions between machines ndash helping
to initiate and manage them
5
OSI Model and Protocol Layering
bull Layer 4 ndash Transport Layerbull Reliable communication stream between two
systems
bull Layer 3 ndash Network Layerbull Responsible for moving data from one system
through routers to destination system
bull Layer 2 ndash Data Link Layerbull Moves data across one hop of the network
bull Layer 1 ndash Physical Layerbull Transmits bits over physical medium ndash copper
fiber radio link or any other medium
6
Current Internet Model
bull Current Internet maps to bottom 5 layers of the OSI modelndash Wraps the top 3 layers into application layerndash Everything above transport layer is application
responsibilityndash Looks like this hellip
7
Current Internet Modelbull Hybrid OSI Architecture
ndash Combines TCPIP standards at layers 3-5 withndash OSI standards at layers 1-2
OSI Hybrid TCPIP-OSI
Application
Presentation
Session
Application
Transport Transport
Network Internet
Data Link Data Link
Physical Physical
TCP
IP
8
Data Link and Physical
bull IEEE 802 specs focus on lower two layers of OSI modelndash Incorporate both physical and link
componentsndash All 802 networks have both a MAC (Media
Access Control) and a physical (PHY) component
9
Data Link Layer
bull Review data link layer specifics including Ethernetndash Protocol defines packet format typically called
frames where each frame encapsulates one packet from network layer
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
5
OSI Model and Protocol Layering
bull Layer 4 ndash Transport Layerbull Reliable communication stream between two
systems
bull Layer 3 ndash Network Layerbull Responsible for moving data from one system
through routers to destination system
bull Layer 2 ndash Data Link Layerbull Moves data across one hop of the network
bull Layer 1 ndash Physical Layerbull Transmits bits over physical medium ndash copper
fiber radio link or any other medium
6
Current Internet Model
bull Current Internet maps to bottom 5 layers of the OSI modelndash Wraps the top 3 layers into application layerndash Everything above transport layer is application
responsibilityndash Looks like this hellip
7
Current Internet Modelbull Hybrid OSI Architecture
ndash Combines TCPIP standards at layers 3-5 withndash OSI standards at layers 1-2
OSI Hybrid TCPIP-OSI
Application
Presentation
Session
Application
Transport Transport
Network Internet
Data Link Data Link
Physical Physical
TCP
IP
8
Data Link and Physical
bull IEEE 802 specs focus on lower two layers of OSI modelndash Incorporate both physical and link
componentsndash All 802 networks have both a MAC (Media
Access Control) and a physical (PHY) component
9
Data Link Layer
bull Review data link layer specifics including Ethernetndash Protocol defines packet format typically called
frames where each frame encapsulates one packet from network layer
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
6
Current Internet Model
bull Current Internet maps to bottom 5 layers of the OSI modelndash Wraps the top 3 layers into application layerndash Everything above transport layer is application
responsibilityndash Looks like this hellip
7
Current Internet Modelbull Hybrid OSI Architecture
ndash Combines TCPIP standards at layers 3-5 withndash OSI standards at layers 1-2
OSI Hybrid TCPIP-OSI
Application
Presentation
Session
Application
Transport Transport
Network Internet
Data Link Data Link
Physical Physical
TCP
IP
8
Data Link and Physical
bull IEEE 802 specs focus on lower two layers of OSI modelndash Incorporate both physical and link
componentsndash All 802 networks have both a MAC (Media
Access Control) and a physical (PHY) component
9
Data Link Layer
bull Review data link layer specifics including Ethernetndash Protocol defines packet format typically called
frames where each frame encapsulates one packet from network layer
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
7
Current Internet Modelbull Hybrid OSI Architecture
ndash Combines TCPIP standards at layers 3-5 withndash OSI standards at layers 1-2
OSI Hybrid TCPIP-OSI
Application
Presentation
Session
Application
Transport Transport
Network Internet
Data Link Data Link
Physical Physical
TCP
IP
8
Data Link and Physical
bull IEEE 802 specs focus on lower two layers of OSI modelndash Incorporate both physical and link
componentsndash All 802 networks have both a MAC (Media
Access Control) and a physical (PHY) component
9
Data Link Layer
bull Review data link layer specifics including Ethernetndash Protocol defines packet format typically called
frames where each frame encapsulates one packet from network layer
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
8
Data Link and Physical
bull IEEE 802 specs focus on lower two layers of OSI modelndash Incorporate both physical and link
componentsndash All 802 networks have both a MAC (Media
Access Control) and a physical (PHY) component
9
Data Link Layer
bull Review data link layer specifics including Ethernetndash Protocol defines packet format typically called
frames where each frame encapsulates one packet from network layer
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
9
Data Link Layer
bull Review data link layer specifics including Ethernetndash Protocol defines packet format typically called
frames where each frame encapsulates one packet from network layer
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
10
Data Link Layer
bull Difference in responsibility between ndash Network layer
bull Has end-to-end job bull Moves transport-layer packets from source to
destination hosts
ndash Link layer bull Has node-to-node job of moving network-layer
packets over a single link in the pathbull Multiple protocols accomplish thisbull Both Ethernet and wireless for example
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
11
Link Layer Servicesbull Framing link access
ndash Encapsulate datagram into frame adding header trailerndash Channel access if shared mediumndash ldquoMACrdquo addresses used in frame headers to identify
source dest bull different from IP address
bull Reliable delivery between adjacent nodesndash Seldom used on low bit-error link (fiber some twisted
pair)ndash But Wireless links much high error ratesndash Why
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
12
Link Layer Services (more)bull Flow control
ndash Pacing between adjacent sending and receiving nodes
bull Error detectionndash Errors caused by signal attenuation noise ndash Receiver detects presence of errors
bull Signals sender for retransmission or drops frame
bull Error correctionndash Receiver identifies and corrects bit error(s) without
resorting to retransmission
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
13
Where is the link layer implemented
bull In every hostbull Link layer implemented
in ldquoadaptorrdquo network interface card
bull Ethernet card PCMCI card 80211 card
bull implements link physical layer
bull Attaches to system buses ndash hardware software and firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
14
Adaptors Communicating
bull Sending sidendash encapsulates datagram in
framendash adds error checking bits
rdt flow control etc
bull Receiving sidendash looks for errors rdt flow
control etcndash extracts datagram passes to
upper layer at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
15
Multiple Access Links and ProtocolsTwo types of ldquolinksrdquobull Point-to-point
ndash PPP for dial-up accessndash point-to-point link between Ethernet switch and
host
bull Broadcast (shared wire or medium)bull old-fashioned Ethernetbull upstream HFCbull 80211 wireless LAN
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
16
Multiple Access protocolsbull Shared broadcast channel
ndash Must have way of sharing mediumndash Two or more simultaneous transmissions by nodes
bull Interference collision if node receives two or more signals at the same time
Multiple access protocolbull Distributed algorithm that determines how nodes
share channel ie determine when node can transmit
bull Communication about channel sharing must use channel itself ndash No out-of-band channel for coordination
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
17
Multiple Access protocols
bull As humans we have following rulesndash Give everyone a chance to speakndash Donrsquot speak until you are spoken tondash Donrsquot monopolize the conversationndash Raise your hand if you have a questionndash Donrsquot interrupt when someone is speakingndash Donrsquot fall asleep when someone is talking
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
18
Ideal Multiple Access Protocol
Broadcast channel of rate R bps
1 When one node wants to transmit it can send at rate R
2 When M nodes want to transmit each can send at average rate RM
3 Rully decentralizedndash no special node to coordinate transmissionsndash no synchronization of clocks slots
4 Simple
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
19
MAC Protocols a taxonomy
Three broad classesbull Channel Partitioning
ndash Divide channel into smaller ldquopiecesrdquo (time slots frequency code)
ndash Allocate piece to node for exclusive use
bull Random Accessndash Channel not divided allow collisions
ndash ldquorecoverrdquo from collisions
bull ldquoTaking turnsrdquondash Nodes take turns but nodes with more to send can
take longer turns
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
20
Channel Partitioning MAC protocols TDMA
TDMA time division multiple access bull Access to channel in rounds bull Each station gets fixed length slot (length = pkt trans
time) in each round bull Unused slots go idle bull Example 6-station LAN 134 have pkt slots 256
idle
1 3 4 1 3 4
6-slotframe
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
21
Channel Partitioning MAC protocols FDMA
FDMA frequency division multiple access ndash Channel spectrum divided into frequency
bandsndash Each station assigned fixed frequency bandndash Unused transmission time in frequency bands
go idle fr
equ
ency
bands time
FDM cable
134 - data
256 - idle
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
22
Random Access Protocolsbull When node has packet to send
ndash transmit at full channel data rate Rndash no a priori coordination among nodes
bull two or more transmitting nodes ldquocollisionrdquobull Random access MAC protocol specifies
ndash how to detect collisionsndash how to recover from collisions (eg via delayed retransmissions)
bull Examples of random access MAC protocolsndash slotted ALOHAndash ALOHAndash CSMA CSMACD CSMACA
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
23
Slotted ALOHAAssumptionsbull All frames same size
ndash time divided into equal size slots (time to transmit 1 frame)
ndash nodes start to transmit only slot beginning
ndash nodes are synchronized
ndash if 2 or more nodes transmit in slot all nodes detect collision
Operationbull When node obtains fresh
frame transmits in next slotndash if no collision node
can send new frame in next slot
ndash if collision node retransmits frame in each subsequent slot with prob p until success
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
24
Slotted ALOHA
Prosbull Single active node can
continuously transmit at full rate of channel
bull Highly decentralized only slots in nodes need to be in sync
bull Simple
Consbull Collisions wasting slotsbull Idle slotsbull Nodes may be able to
detect collision in less than time to transmit packet
bull Clock synchronization
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
25
Slotted Aloha efficiency
bull suppose N nodes with many frames to send each transmits in slot with probability p
bull prob that given node has success in a slot = p(1-p)N-
1
bull prob that any node has a success = Np(1-p)N-1
bull max efficiency find p that maximizes Np(1-p)N-1
bull for many nodes take limit of Np(1-p)N-1 as N goes to infinity gives
Max efficiency = 1e = 37
Efficiency long-run fraction of successful slots (many nodes all with many frames to send)
At best channelused for useful transmissions 37of time
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
26
CSMA (Carrier Sense Multiple Access)
CSMAbull Listen before transmitbull If channel sensed idle transmit entire framebull If channel sensed busy defer transmission
bull Human analogyDonrsquot interrupt others
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
27
CSMA collisions
Collisions can still occurPropagation delay means two nodes may not ldquohearrdquoeach otherrsquos transmissionCollisionEntire packet transmission time wasted ndash Get damaged frames
spatial layout of nodes
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
28
CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA
ndash Collisions detected within short timendash Colliding transmissions aborted reducing channel
wastage
bull Collision detection bull Easy in wired LANs measure signal strengths
compare transmitted received signalsbull Difficult in wireless LANs received signal
strength overwhelmed by local transmission strength
Human analogythe polite conversationalist
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
29
CSMACD collision detection
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
30
ldquoTaking Turnsrdquo MAC protocolsChannel partitioning MAC protocols
ndash share channel efficiently and fairly at high loadndash inefficient at low load delay in channel access 1N
bandwidth allocated even if only 1 active node
Random access MAC protocolsndash Efficient at low load single node can fully utilize
channelndash High load collision overhead
ldquotaking turnsrdquo protocolsLook for best of both worlds
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
31
ldquoTaking Turnsrdquo MAC protocolsPolling bull master node ldquoinvitesrdquo
slave nodes to transmit in turn
bull typically used with ldquodumbrdquo slave devices
bull concernsndash polling overhead ndash latencyndash single point of failure
(master)
master
slaves
poll
data
data
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
32
ldquoTaking Turnsrdquo MAC protocolsToken passingbull control token passed
from one node to next sequentially
bull token messagebull concerns
ndash token overhead ndash latencyndash single point of failure
(token)
T
data
(nothingto send)
T
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
33
Summary of MAC protocolsbull channel partitioning by time frequency or
codendash Time Division Frequency Division
bull random access (dynamic) ndash ALOHA S-ALOHA CSMA CSMACDndash carrier sensing easy in some technologies (wire)
hard in others (wireless)ndash CSMACD used in Ethernetndash CSMACA used in 80211
bull taking turnsndash polling from central site token passingndash Bluetooth FDDI IBM Token Ring
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
34
EthernetldquoDominantrdquo wired LAN technology bull Cheap $20 for NICbull First widely used LAN technologybull Simpler cheaper than token LANs and ATMbull Kept up with speed race 10 Mbps ndash 10 Gbps
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
35
Ethernet History
bull The IEEE 8023 standard is for a CSMACD LANndash Ethernet is a specific product that almost
implements this standard (Ethernet differs from standard in one header field)
ndash Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium
ndash Who founded Ethernet
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
36
Ethernet Operation
bull Common cable providing communication channel was likened to the ether and it was from this reference that the name Ethernet was derived
bull Ethernet stations communicate with each other by sending each other data packets
bull As with other IEEE 802 LANs each Ethernet station is given a single 48-bit MAC address which is used both to specify the destination and the source of each data packet
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
37
Star topologybull Bus topology popular through mid 90s
ndash All nodes in same collision domain (can collide with each other)
bull Today star topology prevailsndash Active switch in centerndash Each ldquospokerdquo runs a (separate) Ethernet protocol (nodes
do not collide with each other)
switch
bus coaxial cable star
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
38
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble bull 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011bull used to synchronize receiver sender clock rates
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
39
Ethernet Frame Structure (more)bull Addresses 6 bytes
ndash if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
ndash otherwise adapter discards framebull Type indicates higher layer protocol (mostly IP but
others possible eg Novell IPX AppleTalk)bull CRC checked at receiver if error is detected frame
is dropped
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
40
Ethernet Unreliable connectionless
bull Connectionless No handshaking between sending and receiving NICs
bull Unreliable receiving NIC doesnrsquot send acks or nacks to sending NICndash Stream of datagrams passed to network layer can
have gaps (missing datagrams)ndash Gaps will be filled if app is using TCPndash Otherwise app will see gaps if based on UDP
bull Ethernetrsquos MAC protocol unslotted CSMACD
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
41
Ethernet CSMACD algorithm1 NIC receives datagram
from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
42
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 bull Goal adapt retransmission
attempts to estimated current loadndash heavy load random wait
will be longerbull first collision choose K
from 01 delay is K 512 bit transmission times
bull after second collision choose K from 0123hellip
bull after ten collisions choose K from 01234hellip1023
Seeinteract with Javaapplet on AWL Web sitehighly recommended
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
43
CSMACD efficiencybull Tprop = max prop delay between 2 nodes in LAN
bull ttrans = time to transmit max-size frame
bull efficiency goes to 1 ndash as tprop goes to 0
ndash as ttrans goes to infinity
bull better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
51
1
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
44
8023 Ethernet Standards Link amp Physical Layers
bull Many different Ethernet standardsndash Common MAC protocol and frame formatndash Different speeds 2 Mbps 10 Mbps 100 Mbps
1Gbps 10G bpsndash Different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
45
bull 80211 History and Brief Facts
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
46
History of Wireless
bull 80211 working group ndash Established in 1990 by IEEE Executive
Committeendash Goal was to create a wireless local area
network (WLAN) standardndash Standard specified an operating frequency in
the 24GHz ISM (Industrial Scientific and Medical) band
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
47
History of Wireless80211 Specifications
bull Pre-standard solution to wireless LANndash Introduced in 1993ndash Based on frequency hopping spread spectrum
technology in the 24 - 2483 GHz bandndash Uncompressed data rate of 16 Mbps and 800
Kbps fallback ndash Multiple channels can support up to 15
wireless LAN connections
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
48
History of Wireless80211 Specifications
80211 (basic)
bull Seven years after 80211 working group is formed (1997) hellipndash Group approved IEEE 80211 as worlds first
WLAN standard with data rates of 1 and 2 Mbps
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
49
History of Wireless80211 Specifications
80211 (ldquoardquo and ldquobrdquo)bull In 1999 the working group approved two
extensions to 80211ndash 80211a - 5GHz band
bull Operates at 54 Mbps (due to higher frequency) bull Only allow access to clients within 40 ndash50 feet
due to power limits enforced by the FCC
ndash 80211b - 24GHz ISM band bull Operates at 11 Mbps bull Allows client access up to well over 1000 feet
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
50
History of Wireless80211 Specifications
80211 (ldquogrdquo)
bull Introduced in June 2003 (though early adoption began in January 2003)ndash Utilizes Orthogonal Frequency Division
Multiplexing (OFDM similar to the operation of 80211a) to acheive 54Mbs connection rates
ndash Backwards compatible with 80211b clients
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
51
History of Wireless80211 (alphabet soup)
bull IEEE 80211 - The original 2 Mbits 24 GHz standard bull IEEE 80211a - 54 Mbits 5 GHz standard (1999)bull IEEE 80211b - Enhancements to 80211 to support 55 and 11
Mbits (1999)bull IEEE 80211d - New countriesbull IEEE 80211e - Enhancements QoS including packet burstingbull IEEE 80211f - Inter-Access Point Protocol (IAPP)bull IEEE 80211g - 54 Mbits 24 GHz standard (backwards
compatible with b) (2003)bull IEEE 80211h - 5 GHz spectrum Dynamic ChannelFrequency
Selection (DCSDFS) and Transmit Power Control (TPC) for European compatibility
bull IEEE 80211i - Enhanced securitybull IEEE 80211j - Extensions for Japanbull IEEE 80211n - Higher throughput improvements
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
52
80211 Protocols
bull 80211 vs 8023ndash 80211 is comparatively complex compared
with traditional Ethernetndash Radio waves as physical layer compared with
wired medium creates a more complicated transmission mechanism
ndash Must account for more unreliable physical medium
ndash Details forthcoming hellip
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-
53
Finish
Next time bull Student presentations of wireless topics and URLrsquos
- CSCD 439539 Wireless Networks and Security
- Introduction
- OSI Model and Protocol Layering
- Slide 4
- Slide 5
- Current Internet Model
- Slide 7
- Data Link and Physical
- Data Link Layer
- Slide 10
- Link Layer Services
- Link Layer Services (more)
- Where is the link layer implemented
- Adaptors Communicating
- Multiple Access Links and Protocols
- Multiple Access protocols
- Slide 17
- Ideal Multiple Access Protocol
- MAC Protocols a taxonomy
- Channel Partitioning MAC protocols TDMA
- Channel Partitioning MAC protocols FDMA
- Random Access Protocols
- Slotted ALOHA
- Slide 24
- Slotted Aloha efficiency
- CSMA (Carrier Sense Multiple Access)
- CSMA collisions
- CSMACD (Collision Detection)
- CSMACD collision detection
- ldquoTaking Turnsrdquo MAC protocols
- Slide 31
- Slide 32
- Summary of MAC protocols
- Ethernet
- Ethernet History
- Ethernet Operation
- Star topology
- Ethernet Frame Structure
- Ethernet Frame Structure (more)
- Ethernet Unreliable connectionless
- Ethernet CSMACD algorithm
- Ethernetrsquos CSMACD (more)
- CSMACD efficiency
- 8023 Ethernet Standards Link amp Physical Layers
- Slide 45
- History of Wireless
- History of Wireless 80211 Specifications
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- 80211 Protocols
- Finish
-