Lec2 Taxonomy
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Transcript of Lec2 Taxonomy
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Taxonomy 1-1
Lec 2: Internet Connectivity:
Packet SwitchingECE5650
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Taxonomy 1-2
Backbone ISPISP ISP
Recap: Internet Physical Structure
Residential access Modem DSL Cable modem Wireless
Campus access Ethernet FDDI Wireless
The Internet is a network ofnetworks Each individually administrated
network is called an AutonomousSystem (AS)
We can roughly divide the networksinto access networks and transitnetworks
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Taxonomy 1-3
Recap: Layered protocol stack
application: supporting networkapplications FTP, SMTP, HTTP
transport: process-process data
transfer TCP, UDP
network: host-host data transfer IP
link: data transfer betweenneighboring network elements PPP, Ethernet
physical:bits on the wire
application
transport
network
link
physical
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Taxonomy 1-4
Recap: Histroy
60s: packet switching theory, ARPNET ARPANET was an attempt to investigate the feasibility
of packet switching ARPANET was built on top of telephone networks
70s: internetworking, Ethernet
80s: applications: email, ftp, telnet, etc 90s: web killer appl and commercialization
totally distributed, autonomous systems roughlyhierarchical where ISPs interconnect at PoP and NAP
Today: As important as utility services backbone speed: about 10 Gbps number of hosts: about 400 millions
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Taxonomy 1-5
Outline
Network Taxonomy Broadcast vs Switched Networks
Circuit Switched vs packet switched
Switched Network Performance Delay, Lose, Throughtput
Security
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Taxonomy 1-6
The Network Core
mesh of interconnectedrouters
thefundamentalquestion: how is datatransferred through net?
circuit switching:dedicated circuit percall: telephone net
packet-switching: datasent thru net indiscrete chunks
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Taxonomy 1-7
Network Core: Circuit Switching
End-end resourcesreserved for call
link bandwidth and
switch capacity pre-determined
dedicated resourceswith no sharing of
bandwidth guaranteed
performance
call setup required
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Taxonomy 1-8
Network Core: Circuit Switching
network resources(e.g., bandwidth)divided into pieces
pieces allocated to calls
resource piece idleifnot used by owning call(no sharing)
dividing link bandwidthinto pieces
frequency division
time division
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Taxonomy 1-9
Circuit Switching: FDM and TDM
Frequency Domain Mux (FDM)
bandwidth/
frequency
of the link
time
Time Domain Mux (TDM)Transmission rate of single circuit = frame rate in frames/sec * #bits in a slot
bandwidth/
frequency
of the link
time
4 users/slots
Example:
Slot4 slots/frame
Note: Circuit is analogous to connection
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Taxonomy 1-10
circuitestablishment
DATAdatatransmission
circuittermination
propagation delayfrom A to Node 1
propagation delayfrom B To A
processing delay at Node 1
Circuit Switching in MultiHop Route
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Taxonomy 1-11
Network Core: Packet Switching
each end-end data streamdivided intopackets
user A, B packets sharenetwork resources
each packet uses full linkbandwidth
resources used as needed
resource contention: flow-control needed as
aggregate resourcedemand can exceed
amount available congestion control
needed as packetsqueued and wait for
link use store and forward:
packets move one hopat a time
Bandwidth division into piecesDedicated allocation
Resource reservation
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Taxonomy 1-12
Packet Switching: Statistical Multiplexing
Sequence of A & B packets does not have fixed pattern,on demand sharing of resources (statisticalmultiplexing).
A
B
C10 Mb/sEthernet
1.5 Mb/s
D E
statistical multiplexing
queue of packetswaiting for outputlink
Header Data Trailer
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Taxonomy 1-13
Host A
Host BHost E
Host D
Host C
Node 1 Node 2
Node 3
Node 4
Node 5
Node 6 Node 7
Packet Switching
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Taxonomy 1-14
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
processingandqueueingdelay ofPacket 1 atrouter 2
propagationdelay fromHost A torouter 1
transmissiontime of Packet 1at Host A
Timing Diagram of Packet Switching
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Taxonomy 1-15
Packet switching vs Circuit Switching: AnExample
Problem: 1 Mbps link and each user needs 100kbps when active and is active 10% of time.
circuit-switching FDM: Max #users = (1,000,000 b/s)/(100,000 b/s) = 10
packet switching: Min #users = 10
Max is > 10 due to the probability that users are
inactive 90% of time
Packet switching allows more users to use network!
N users1 Mbps link
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Taxonomy 1-16
Packet Switching vs Circuit Switching
Great for bursty data
resource sharing
simpler, no call setup Excessive congestion: packet delay and loss
protocols needed for reliable data transfer,congestion control
Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps
still an unsolved problem
Is packet switching a slam dunk winner?
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Taxonomy 1-17
Packet-switched Networks: Forwarding
Goal:move packets through routers from source to dest
(1) Packet-switched datagram network:
destination address in packet determines next hop Entire packet must arrive at router before it can be transmitted
on next link
routes may change during session
analogy: driving, asking directions
(2) Packet-switched virtual circuit network: each packet carries tag (VC ID), tag determines next hop
fixed path determined at call setup time, remains fixed thru call
routers maintainper-call state
L
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Taxonomy 1-18
Host A
Host BHost E
Host D
Host C
Node 1 Node 2
Node 3
Node 4
Node 5
Node 6 Node 7
Virtual-Circuit Switching
Three phases VC establishment
Data transfer
VC disconnect
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Taxonomy 1-19
Virtual-Circuit Packet Switching
Example: Asynchornous Transfer Mode (ATM)networks; Multiple Label Packet Switching (MPLS) inIP networks
Hybrid of circuit switching and datagram switching
each packet carries a shorttag (virtual-circuit (VC) #);tag determines next hop
fixed path determined atVirtual Circuit setup time,
remains fixed thru flow routers maintain per-flow
state what state do routers
maintain for datagram switching?
IncomingInterface
IncomingVC#
OutgoingInterface
OutgoingVC#
1 12 2 22
1 16 3 1
2 12 3 22
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Taxonomy 1-20
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
Host 1 Host 2Node 1 Node 2
propagation delay
between Host 1
and Node 1VC
establishment
VC
termination
data
transfer
Timing Diagram of Virtual-Circuit Switching
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Taxonomy 1-21
Datagram Switching vs. Virtual CircuitSwitching
What are the benefits of datagramswitching over virtual circuit switching?
What are the benefits of virtual circuit
switching over datagram switching?
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Taxonomy 1-22
Network Taxonomy
Broadcast networks Nodes share a common channel; information transmitted
by a node is received by all other nodes in the network
Examples: TV, radio
Switched networks Information is transmitted to a small sub-set (usually
only one) of the nodes
commnetworks
switched
networks
broadcast
networks
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Taxonomy 1-23
Switched Network
Switchednetworks
Circuit-switchednetworks
FDM TDM
Packet-switchednetworks
Networkswith VCs
DatagramNetworks
(Internet)(X.25,Frame relay, ATM)
Course Subject
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Taxonomy 1-24
Outline
Network Taxonomy Broadcast vs Switched Networks Circuit Switched vs packet switched
Switched Network Performance Delay: Loss
Throughput
Security
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Taxonomy 1-25
Delay Calculation in Circuit Switched Networks
Transmission delay:
R = reserved bandwidth(bps)
L = packet length (bits)
time to send a packet
into link = L/R
Propagation delay:
d = length of physical link s = propagation speed in
medium (~2x105 km/sec)
propagation delay = d/s
Propagation delay: delay for the firstbit to go from a source to a destination
Transmission delay: time to pump
data onto link at reservedrate
DATA
d/s
L/R
Time
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Taxonomy 1-26
An Example
Propagation delay suppose the distance between A and B is 4000 km, then
one-way propagation delay is:
Transmission delay suppose we reserve a one slot GSM channel
a GSM frame can transmit about 115 kbps
A GSM frame is divided into 8 slots
each reserved one slot GSM has a bandwidth of about 14 Kbps(=115/8)
then the transmission delay of a packet of 1 Kbits is
msskm
km 20/000,200
4000
mskbps
kbits 7014
1
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Taxonomy 1-27
An Example (cont.) Suppose the setup message is very small, and the total setup
processing delay is 200 ms Then the delay to transfer a packet of 1 Kbits from A to B
(from the beginning until host receives last bit of the file) is:
ms31070202020020
DATA
20 + 200
20
20
70
Host A Host B
time
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Taxonomy 1-28
Another example
How long does it take to send a file of 640,000bits (1 byte=8bits) from host A to host B over acircuit-switched network? All links are 1.536 Mbps (Mega Bits Per Second)
Each link uses TDM with 24 slots/sec 500 msec to establish end-to-end circuit (setup time
including propagation delay)
Single circuit speed = 1.536 Mbps / 24 = 64kbps
File transmission time = 500 msec + file size/speed
= 0.5 sec + 640,000 bits / 64 kbps
= 10.5 sec
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Taxonomy 1-29
How do loss and delay occur inpacket switching?
packets queuein router buffers packet arrival rate to link exceeds output link capacity
packets queue, wait for turn
A
B
packet being transmitted (delay)
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
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Taxonomy 1-30
Four sources of packet delay
1. Processing delay atrouter: check bit errors
determine output link
A
B
propagation
transmission
nodalprocessing queueing
2. Queueing delay atrouter time waiting at output
link for transmission
depends on congestionlevel of router
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Taxonomy 1-31
Delay in packet-switched networks
3. Transmission delay oflink:
R=link bandwidth (bps)
L=packet length (bits)
time to send bits intolink = L/R
4. Propagation delay ofmedium:
d = length of physical link
s = propagation speed in
medium (~2x108 m/sec) propagation delay = d/s
A
B
propagation
transmission
nodal
processing queueing
Note: s and R are verydifferent quantities!
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Taxonomy 1-32
Total Delay in Datagram Networks
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
nodalprocessingand queueing
delay ofPacket 1 atNode 2
propagationdelay betweenHost 1 andNode 2
transmission
time of Packet 1at Host 1
Host 1 Host 2Node 1 Node 2
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Taxonomy 1-33
Total End-End Delay
N = #links between source and destination = #routers + 1
dproc = processing delay at router (task 1)
typically a few microsecs or less
dqueue = queuing delay at router (task 2)
depends on congestion (neglect if light traffic)
dtrans = transmission delay for router to put data on medium (task 3)
= L/R, significant for low-speed links
dprop = propagation delay at medium (task 4) a few microsecs to hundreds of msecs
)()( proptransqueueprocnodalend-end ddddNdNd
N
q
qpropd
qtransd
qqueued
qprocdendend
d1
homogeneous l inks
heterogeneous l inks
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Taxonomy 1-38
Real Internet delays and routes
What do real Internet delay & loss look like?
Traceroute program (in Unix) or Tracert (MS-DOS): provides delay measurement from source torouter along end-end Internet path towardsdestination. For all i: sends three packets that will reach router ion path
towards destination
router iwill return packets to sender
sender times interval between transmission and reply.3 probes
3 probes
3 probes
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Taxonomy 1-39
Real Internet delays and routes
traceroute: jis.mit.edu to wayne state
1 W92-RTR-1-W92SRV21.MIT.EDU (18.7.21.1) 0.435 ms 0.367 ms 0.249 ms
2 EXTERNAL-RTR-1-BACKBONE.MIT.EDU (18.168.0.18) 0.815 ms 0.704 ms 0.539 ms
3 EXTERNAL-RTR-2-BACKBONE.MIT.EDU (18.168.0.27) 20.266 ms 0.667 ms 0.561 ms
4 nox230gw1-Vl-526-NoX-MIT.nox.org (192.5.89.89) 0.659 ms 5.859 ms 0.587 ms5 nox230gw1-PEER-NoX-NOX-192-5-89-10.nox.org (192.5.89.10) 5.844 ms 5.829 ms 5.796 ms
6 chinng-nycmng.abilene.ucaid.edu (198.32.8.82) 35.703 ms 33.674 ms 32.154 ms
7 mren-chin-ge.abilene.ucaid.edu (198.32.11.98) 29.647 ms 33.975 ms 36.040 ms
8 ge-1-3-0x189.aa1.mich.net (192.122.182.17) 31.860 ms 31.891 ms 31.874 ms
9 v27.wsu3.mich.net (198.108.23.133) 33.405 ms 33.480 ms 33.508 ms
10 141.217.154.98 (141.217.154.98) 34.833 ms 33.710 ms 33.698 ms
11 * * *12 * * *
3 delay measures
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Taxonomy 1-40
Real Internet delays and routes
Tracing route to www.yahoo.akadns.net [216.109.118.67]
over a maximum of 30 hops:
1 1 ms 1 ms 1 ms 192.168.0.1
2 11 ms 9 ms 8 ms 64.230.197.241
3 7 ms 7 ms 7 ms 64.230.235.85
4 7 ms 7 ms 7 ms 64.230.235.97
5 12 ms 12 ms 12 ms rtp627197rts [64.230.220.254]6 13 ms 13 ms 12 ms 64.230.242.205
7 12 ms 12 ms 12 ms bx3-toronto12-pos5-0.in.bellnexxia.net [206.108.107.234]
8 13 ms 13 ms 13 ms if-7-0.core1.TTT-Scarborough.teleglobe.net [209.58.25.69]
9 31 ms 32 ms 31 ms if-3-3.mcore3.NJY-Newark.teleglobe.net [216.6.57.33]
10 36 ms 36 ms 36 ms if-13-0.core1.AEQ-Ashburn.teleglobe.net [216.6.57.42]
11 37 ms 36 ms 36 ms ix-14-2.core1.AEQ-Ashburn.teleglobe.net [63.243.149.110]
12 36 ms 36 ms 36 ms vlan200-msr1.dcn.yahoo.com [216.115.96.161]13 35 ms 36 ms 36 ms ge3-1.bas2-m.dcn.yahoo.com [216.109.120.146]
14 36 ms 36 ms 37 ms p4.www.dcn.yahoo.com [216.109.118.67]
Trace complete.
It took 13 routers to get from my house to www.yahoo.com
3 delay (end-end)measurements for each ofthe 3 msgs
Note: an * in one of the routers result means no response (probe lost, router did notreply for at least one of the 3 msgs)
tracert www.yahoo.com
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Taxonomy 1-41
Real Internet delays and routes
Ping program: checks if a host is live or not andprovides RTT delay measurement from source todestination along end-end Internet path. sends n requests of size 32 bytes and calculates avg RTT
sender times interval between transmission and reply. ping -n
nprobes
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Taxonomy 1-42
Real Internet delays and routes
Pinging www.yahoo.akadns.net [68.142.226.34] with 32 bytes of data:
Reply from 68.142.226.34: bytes=32 time=38ms TTL=51
Reply from 68.142.226.34: bytes=32 time=39ms TTL=51
Reply from 68.142.226.34: bytes=32 time=38ms TTL=51
Reply from 68.142.226.34: bytes=32 time=39ms TTL=51
Ping statistics for 68.142.226.34:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:Minimum = 38ms, Maximum = 39ms, Average = 38ms
RTTs
ping www.yahoo.com
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Taxonomy 1-43
Outline
Network Taxonomy Broadcast vs Switched Networks Circuit Switched vs packet switched
Switched Network Performance Performance Metrics:
Delay: Loss
Throughput
Security
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Taxonomy 1-44
Packet loss
queue (aka buffer) preceding link in buffer hasfinite capacity
packet arriving to full queue dropped (aka lost)
lost packet may be retransmitted by previousnode, by source end system, or not at all
A
B
packet being transmitted
packet arriving tofull bufferis lost
buffer(waiting area)
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Taxonomy 1-45
Throughput
throughput:rate (bits/time unit) at whichbits transferred between sender/receiver instantaneous:rate at given point in time
average:rate over long(er) period of time
server, withfile of F bits
to send to client
link capacityRsbits/sec
link capacityRcbits/sec
pipe that can carryfluid at rateRsbits/sec)
pipe that can carryfluid at rateRcbits/sec)
server sends bits(fluid) into pipe
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Taxonomy 1-46
Throughput (more)
Rs< Rc What is average end-end throughput?
Rsbits/sec Rcbits/sec
Rs> Rc What is average end-end throughput?
Rsbits/sec Rc
bits/sec
link on end-end path that constrains end-end throughput
bottleneck link
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Taxonomy 1-47
Throughput: Internet scenario
10 connections (fairly) sharebackbone bottleneck link Rbits/sec
RsRs
Rs
Rc
Rc
Rc
R
per-connectionend-end
throughput:min(Rc,Rs,R/10)
in practice: Rc orR
sis often
bottleneck
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Taxonomy 1-48
Outline
Network Taxonomy Broadcast vs Switched Networks Circuit Switched vs packet switched
Switched Network Performance Performance Metrics:
Delay: Loss
Throughput
Security
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Taxonomy 1-49
Network Security
attacks on Internet infrastructure: infecting/attacking hosts: spyware, virus, worms, Trojan
Horse, unauthorized access, and malware in geneal Malware: sw designed to infiltrate or damage a computer system
w/o the owners informed consent [Wikipedia]; based onintention of its creator, rather than any features
In law, malware is defined as a computer contaminant
denial of service: deny access to resources (servers, link BW) Vulnerability attack; BW flooding; Connection flooding
Internet not originally designed with security in mind
original vision:a group of mutually trusting users attachedto a transparent network
Internet protocol designers playing catch-up
Security considerations in all layers!
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Taxonomy 1-50
What can bad guys do: malware?
Spyware: infection by downloading
web page with spyware
records keystrokes, websites visited, upload infoto collection site
Virus infection by receiving
object (e.g., e-mail
attachment), activelyexecuting
self-replicating:propagate itself toother hosts, users
Worm: infection by passively
receiving object that getsitself executed
self- replicating: propagatesto other hosts, users
Sapphire Worm in 2003: aggregate scans/sec
in first 5 minutes of outbreak (CAIDA, UWisc data)
Double in every 8.5 sec
90% infected in 10 min
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Taxonomy 1-51
Denial of service attacks
attackers make resources (server, bandwidth)unavailable to legitimate traffic by overwhelmingresource with bogus traffic
1. select target
2. break into hostsaround the network(collectively, known asbotnet)
3. send packets towardtarget fromcompromised hosts
target
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Taxonomy 1-52
Sniff, modify, delete your packets
Packet sniffing: broadcast media (shared Ethernet, wireless)
promiscuous network interface reads/records allpackets (e.g., including passwords!) passing by
A
B
C
src:B dest:A payload
Ethereal (Wireshark) software used for end-of-chapter labs is a (free) packet-sniffer
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Taxonomy 1-53
Masquerade as you
IP spoofing:send packet with false source address
A
B
C
src:B dest:A payload
M squ d s u
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Taxonomy 1-54
Masquerade as youMan-in-the-middle attack
IP spoofing:send packet with false source address record-and-playback: sniff sensitive info (e.g.,
password), and use later
password holder isthat user from system point of
view
A
B
C
src:B dest:A user: B; password: foo
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Taxonomy 1-55
Masquerade as you
IP spoofing:send packet with false source address record-and-playback: sniff sensitive info (e.g.,
password), and use later
password holder isthat user from system point of
view
A
B
later ..C
src:B dest:A user: B; password: foo
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Summary
Network Taxonomy Broadcast
Circuit Switch
Packet switch Virtual circuit switch
Switched Network Performance Delay, packet loss, throughput
Security