CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC...

25
1 CPSC 441: Review 1 CPSC 441: Review (W06) Instructor: Dr. Anirban Mahanti Office: ICT 745 Email: [email protected] Date: April 12, 2006 Text Book Computer Networking: A Top Down Approach Featuring the Internet”, 3 rd edition, Jim Kurose and Keith Ross Addison-Wesley, 2005. CPSC 441: Review 2 Outline Introduction Applications Transport Layer Network Layer LANs and WLANs Multimedia Networking Questions CPSC 441: Review 3 Reference Models OSI model: 7-layer model; application, presentation, session, transport, network, data link, and physical. TCP/IP model: 4-layers; application, transport, Internet, and Host-to-Network. Internet Protocol Stack – a hybrid of TCP/IP and OSI reference models

Transcript of CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC...

Page 1: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

1

CPSC 441 Review 1

CPSC 441 Review (W06)Instructor Dr Anirban MahantiOffice ICT 745Email mahanticpscucalgarycaDate April 12 2006

Text BookldquoComputer Networking A Top Down Approach

Featuring the Internetrdquo 3rd edition Jim Kurose and Keith Ross Addison-Wesley 2005

CPSC 441 Review 2

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 3

Reference Models

OSI model 7-layer model application presentation session transport network data link and physical

TCPIP model 4-layers application transport Internet and Host-to-Network

Internet Protocol Stack ndash a hybrid of TCPIP and OSI reference models

2

CPSC 441 Review 4

Layers and Protocols

Layered network architecture hellip whyReduces design complexity

The purpose of a layerLayer-N peers converse with each other using protocols each layer provides functionality to the a higher layer

ProtocolsA set of rules governing the format and meaning of messages exchanges by peer entities within a layer

CPSC 441 Review 5

Protocols Layers and PDUrsquos

Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 6

More on Layers and Protocols

Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211

Assuming the Internet Protocol Stack

3

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo

Virtual circuit vs datagram networksCircuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo

TDMA FDMACircuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

4

CPSC 441 Review 10

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networksWhat is HTTP

Hypertext Transfer Protocol ndash the Webrsquos application layer protocolHTTP 10 HTTP 11Pipelined ndash requests sent as soon as it is encounteredPersistent ndash multiple objects can be sent over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headersHow is the end of an object determined in HTTP11

HTTP methodsGET HEAD POST PUT hellip

HTTP response codes1xx 2xx 3xx 4xx 5xx

5

CPSC 441 Review 13

The World Wide Web

What is a Web ProxyWhat is a caching hierarchyCaching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issuesPrefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hostsIP address (32 bit) - used for addressing datagramsldquonamerdquo eg wwyahoocom - used by humans

DNS provides translation between host name and IP address

distributed database implemented in hierarchy of many name serversDistributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translationHost aliasing

Canonical and alias namesMail server aliasingLoad distribution

Replicated Web servers set of IP addresses for one canonical name

6

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyeduwants IP address for gaiacsumasseduInfrastructure

Client resolverLocal DNS serverAuthoritative DNS ServerRoot DNS ServerTop-Level Domain DNS Server

CPSC 441 Review 17

Electronic Mail

Three major componentsuser agents

eg Eudora Outlook Pine Netscape Messenger

mail servers Incoming outgoing messages

Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

7

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systemsMultiplexingde-multiplexingService models UDP vs TCP

UDP provides multiplexingde-multiplexingIn addition to the above TCP provides flow control congestion control and reliable data deliverySome applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquoprotocolsACK NAK SACKPerformance of ldquostop-and-waitrdquo

PipeliningSimilaritydifferences between TCP and the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

8

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numberingTTLChecksum ndash compulsory in TCP but not in UDPHandshaking procedures during TCP connection set-up and connection termination

SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

9

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion ControlCongestion informally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Packet loss (buffer overflow at routers)Increased end-to-end delays (queuing in router buffers)

Results in unfairness and poor utilization of network resources

Resources used by dropped packets (before they were lost)RetransmissionsPoor resource allocation at high load

CPSC 441 Review 27

Congestion Control ApproachesGoal Throttle senders as needed to ensure load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systemssingle bit indicating congestion (eg ECN)explicit rate sender should send at

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 2: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

2

CPSC 441 Review 4

Layers and Protocols

Layered network architecture hellip whyReduces design complexity

The purpose of a layerLayer-N peers converse with each other using protocols each layer provides functionality to the a higher layer

ProtocolsA set of rules governing the format and meaning of messages exchanges by peer entities within a layer

CPSC 441 Review 5

Protocols Layers and PDUrsquos

Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 6

More on Layers and Protocols

Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211

Assuming the Internet Protocol Stack

3

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo

Virtual circuit vs datagram networksCircuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo

TDMA FDMACircuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

4

CPSC 441 Review 10

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networksWhat is HTTP

Hypertext Transfer Protocol ndash the Webrsquos application layer protocolHTTP 10 HTTP 11Pipelined ndash requests sent as soon as it is encounteredPersistent ndash multiple objects can be sent over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headersHow is the end of an object determined in HTTP11

HTTP methodsGET HEAD POST PUT hellip

HTTP response codes1xx 2xx 3xx 4xx 5xx

5

CPSC 441 Review 13

The World Wide Web

What is a Web ProxyWhat is a caching hierarchyCaching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issuesPrefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hostsIP address (32 bit) - used for addressing datagramsldquonamerdquo eg wwyahoocom - used by humans

DNS provides translation between host name and IP address

distributed database implemented in hierarchy of many name serversDistributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translationHost aliasing

Canonical and alias namesMail server aliasingLoad distribution

Replicated Web servers set of IP addresses for one canonical name

6

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyeduwants IP address for gaiacsumasseduInfrastructure

Client resolverLocal DNS serverAuthoritative DNS ServerRoot DNS ServerTop-Level Domain DNS Server

CPSC 441 Review 17

Electronic Mail

Three major componentsuser agents

eg Eudora Outlook Pine Netscape Messenger

mail servers Incoming outgoing messages

Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

7

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systemsMultiplexingde-multiplexingService models UDP vs TCP

UDP provides multiplexingde-multiplexingIn addition to the above TCP provides flow control congestion control and reliable data deliverySome applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquoprotocolsACK NAK SACKPerformance of ldquostop-and-waitrdquo

PipeliningSimilaritydifferences between TCP and the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

8

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numberingTTLChecksum ndash compulsory in TCP but not in UDPHandshaking procedures during TCP connection set-up and connection termination

SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

9

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion ControlCongestion informally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Packet loss (buffer overflow at routers)Increased end-to-end delays (queuing in router buffers)

Results in unfairness and poor utilization of network resources

Resources used by dropped packets (before they were lost)RetransmissionsPoor resource allocation at high load

CPSC 441 Review 27

Congestion Control ApproachesGoal Throttle senders as needed to ensure load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systemssingle bit indicating congestion (eg ECN)explicit rate sender should send at

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 3: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

3

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo

Virtual circuit vs datagram networksCircuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo

TDMA FDMACircuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

4

CPSC 441 Review 10

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networksWhat is HTTP

Hypertext Transfer Protocol ndash the Webrsquos application layer protocolHTTP 10 HTTP 11Pipelined ndash requests sent as soon as it is encounteredPersistent ndash multiple objects can be sent over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headersHow is the end of an object determined in HTTP11

HTTP methodsGET HEAD POST PUT hellip

HTTP response codes1xx 2xx 3xx 4xx 5xx

5

CPSC 441 Review 13

The World Wide Web

What is a Web ProxyWhat is a caching hierarchyCaching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issuesPrefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hostsIP address (32 bit) - used for addressing datagramsldquonamerdquo eg wwyahoocom - used by humans

DNS provides translation between host name and IP address

distributed database implemented in hierarchy of many name serversDistributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translationHost aliasing

Canonical and alias namesMail server aliasingLoad distribution

Replicated Web servers set of IP addresses for one canonical name

6

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyeduwants IP address for gaiacsumasseduInfrastructure

Client resolverLocal DNS serverAuthoritative DNS ServerRoot DNS ServerTop-Level Domain DNS Server

CPSC 441 Review 17

Electronic Mail

Three major componentsuser agents

eg Eudora Outlook Pine Netscape Messenger

mail servers Incoming outgoing messages

Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

7

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systemsMultiplexingde-multiplexingService models UDP vs TCP

UDP provides multiplexingde-multiplexingIn addition to the above TCP provides flow control congestion control and reliable data deliverySome applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquoprotocolsACK NAK SACKPerformance of ldquostop-and-waitrdquo

PipeliningSimilaritydifferences between TCP and the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

8

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numberingTTLChecksum ndash compulsory in TCP but not in UDPHandshaking procedures during TCP connection set-up and connection termination

SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

9

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion ControlCongestion informally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Packet loss (buffer overflow at routers)Increased end-to-end delays (queuing in router buffers)

Results in unfairness and poor utilization of network resources

Resources used by dropped packets (before they were lost)RetransmissionsPoor resource allocation at high load

CPSC 441 Review 27

Congestion Control ApproachesGoal Throttle senders as needed to ensure load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systemssingle bit indicating congestion (eg ECN)explicit rate sender should send at

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 4: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

4

CPSC 441 Review 10

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networksWhat is HTTP

Hypertext Transfer Protocol ndash the Webrsquos application layer protocolHTTP 10 HTTP 11Pipelined ndash requests sent as soon as it is encounteredPersistent ndash multiple objects can be sent over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headersHow is the end of an object determined in HTTP11

HTTP methodsGET HEAD POST PUT hellip

HTTP response codes1xx 2xx 3xx 4xx 5xx

5

CPSC 441 Review 13

The World Wide Web

What is a Web ProxyWhat is a caching hierarchyCaching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issuesPrefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hostsIP address (32 bit) - used for addressing datagramsldquonamerdquo eg wwyahoocom - used by humans

DNS provides translation between host name and IP address

distributed database implemented in hierarchy of many name serversDistributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translationHost aliasing

Canonical and alias namesMail server aliasingLoad distribution

Replicated Web servers set of IP addresses for one canonical name

6

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyeduwants IP address for gaiacsumasseduInfrastructure

Client resolverLocal DNS serverAuthoritative DNS ServerRoot DNS ServerTop-Level Domain DNS Server

CPSC 441 Review 17

Electronic Mail

Three major componentsuser agents

eg Eudora Outlook Pine Netscape Messenger

mail servers Incoming outgoing messages

Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

7

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systemsMultiplexingde-multiplexingService models UDP vs TCP

UDP provides multiplexingde-multiplexingIn addition to the above TCP provides flow control congestion control and reliable data deliverySome applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquoprotocolsACK NAK SACKPerformance of ldquostop-and-waitrdquo

PipeliningSimilaritydifferences between TCP and the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

8

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numberingTTLChecksum ndash compulsory in TCP but not in UDPHandshaking procedures during TCP connection set-up and connection termination

SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

9

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion ControlCongestion informally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Packet loss (buffer overflow at routers)Increased end-to-end delays (queuing in router buffers)

Results in unfairness and poor utilization of network resources

Resources used by dropped packets (before they were lost)RetransmissionsPoor resource allocation at high load

CPSC 441 Review 27

Congestion Control ApproachesGoal Throttle senders as needed to ensure load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systemssingle bit indicating congestion (eg ECN)explicit rate sender should send at

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 5: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

5

CPSC 441 Review 13

The World Wide Web

What is a Web ProxyWhat is a caching hierarchyCaching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issuesPrefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hostsIP address (32 bit) - used for addressing datagramsldquonamerdquo eg wwyahoocom - used by humans

DNS provides translation between host name and IP address

distributed database implemented in hierarchy of many name serversDistributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translationHost aliasing

Canonical and alias namesMail server aliasingLoad distribution

Replicated Web servers set of IP addresses for one canonical name

6

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyeduwants IP address for gaiacsumasseduInfrastructure

Client resolverLocal DNS serverAuthoritative DNS ServerRoot DNS ServerTop-Level Domain DNS Server

CPSC 441 Review 17

Electronic Mail

Three major componentsuser agents

eg Eudora Outlook Pine Netscape Messenger

mail servers Incoming outgoing messages

Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

7

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systemsMultiplexingde-multiplexingService models UDP vs TCP

UDP provides multiplexingde-multiplexingIn addition to the above TCP provides flow control congestion control and reliable data deliverySome applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquoprotocolsACK NAK SACKPerformance of ldquostop-and-waitrdquo

PipeliningSimilaritydifferences between TCP and the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

8

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numberingTTLChecksum ndash compulsory in TCP but not in UDPHandshaking procedures during TCP connection set-up and connection termination

SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

9

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion ControlCongestion informally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Packet loss (buffer overflow at routers)Increased end-to-end delays (queuing in router buffers)

Results in unfairness and poor utilization of network resources

Resources used by dropped packets (before they were lost)RetransmissionsPoor resource allocation at high load

CPSC 441 Review 27

Congestion Control ApproachesGoal Throttle senders as needed to ensure load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systemssingle bit indicating congestion (eg ECN)explicit rate sender should send at

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 6: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

6

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyeduwants IP address for gaiacsumasseduInfrastructure

Client resolverLocal DNS serverAuthoritative DNS ServerRoot DNS ServerTop-Level Domain DNS Server

CPSC 441 Review 17

Electronic Mail

Three major componentsuser agents

eg Eudora Outlook Pine Netscape Messenger

mail servers Incoming outgoing messages

Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

7

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systemsMultiplexingde-multiplexingService models UDP vs TCP

UDP provides multiplexingde-multiplexingIn addition to the above TCP provides flow control congestion control and reliable data deliverySome applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquoprotocolsACK NAK SACKPerformance of ldquostop-and-waitrdquo

PipeliningSimilaritydifferences between TCP and the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

8

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numberingTTLChecksum ndash compulsory in TCP but not in UDPHandshaking procedures during TCP connection set-up and connection termination

SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

9

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion ControlCongestion informally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Packet loss (buffer overflow at routers)Increased end-to-end delays (queuing in router buffers)

Results in unfairness and poor utilization of network resources

Resources used by dropped packets (before they were lost)RetransmissionsPoor resource allocation at high load

CPSC 441 Review 27

Congestion Control ApproachesGoal Throttle senders as needed to ensure load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systemssingle bit indicating congestion (eg ECN)explicit rate sender should send at

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 7: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

7

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systemsMultiplexingde-multiplexingService models UDP vs TCP

UDP provides multiplexingde-multiplexingIn addition to the above TCP provides flow control congestion control and reliable data deliverySome applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquoprotocolsACK NAK SACKPerformance of ldquostop-and-waitrdquo

PipeliningSimilaritydifferences between TCP and the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

8

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numberingTTLChecksum ndash compulsory in TCP but not in UDPHandshaking procedures during TCP connection set-up and connection termination

SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

9

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion ControlCongestion informally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Packet loss (buffer overflow at routers)Increased end-to-end delays (queuing in router buffers)

Results in unfairness and poor utilization of network resources

Resources used by dropped packets (before they were lost)RetransmissionsPoor resource allocation at high load

CPSC 441 Review 27

Congestion Control ApproachesGoal Throttle senders as needed to ensure load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systemssingle bit indicating congestion (eg ECN)explicit rate sender should send at

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 8: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

8

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numberingTTLChecksum ndash compulsory in TCP but not in UDPHandshaking procedures during TCP connection set-up and connection termination

SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

9

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion ControlCongestion informally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Packet loss (buffer overflow at routers)Increased end-to-end delays (queuing in router buffers)

Results in unfairness and poor utilization of network resources

Resources used by dropped packets (before they were lost)RetransmissionsPoor resource allocation at high load

CPSC 441 Review 27

Congestion Control ApproachesGoal Throttle senders as needed to ensure load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systemssingle bit indicating congestion (eg ECN)explicit rate sender should send at

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 9: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

9

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion ControlCongestion informally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Packet loss (buffer overflow at routers)Increased end-to-end delays (queuing in router buffers)

Results in unfairness and poor utilization of network resources

Resources used by dropped packets (before they were lost)RetransmissionsPoor resource allocation at high load

CPSC 441 Review 27

Congestion Control ApproachesGoal Throttle senders as needed to ensure load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systemssingle bit indicating congestion (eg ECN)explicit rate sender should send at

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 10: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

10

CPSC 441 Review 28

TCP Congestion Control Overview

end-end control (no network assistance)Limit the number of packets in the network to window WRoughly

W is dynamic function of perceived network congestion

rate = WRTT Bytessec

CPSC 441 Review 29

TCP Congestion ControlsTahoe (Jacobson 1988)

Slow StartCongestion AvoidanceFast Retransmit

Reno (Jacobson 1990)Fast Recovery

CPSC 441 Review 30

TCP TahoeBasic ideas

Gently probe network for spare capacityDrastically reduce rate on congestionWindowing self-clockingOther functions round trip time estimation error recovery

for every ACK if (W lt ssthresh) then W++ (SS)else W += 1W (CA)

for every loss

ssthresh = W2W = 1

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 11: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

11

CPSC 441 Review 31

TCP Reno Fast RecoveryObjective prevent `pipersquo from emptying after fast retransmit

each dup ACK represents a packet having left the pipe (successfully received)Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh larr W2retransmit lost packetW larr ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W larr ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow startOn 3 duplicate ACKs

Fast retransmit and fast recoveryOn timeout

Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno ThroughputAverage throughout 75 WRTTThroughput in terms of loss rate

What happens if L-gt0Does link capacity matter if we experience random lossHigh-speed TCP

LRTTMSSsdot221

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 12: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

12

CPSC 441 Review 34

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving hostNetwork layer protocols in every host router [contrast with transportapplication layer]Main functions of network layer

Forwarding ndash moving datagrams within a routerRouting ndash determine end-to-end paths taken by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifierInternetchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgs fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP20 bytes of TCP20 bytes of IP= 40 bytes + app layer overhead

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 13: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

13

CPSC 441 Review 37

IPv4 AddressingIP address 32-bit identifier for host router interfaceinterface connection between hostrouter and physical link

routerrsquos typically have multiple interfaceshost may have multiple interfacesIP addresses associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful AddressingAddresses consists of

Network partHost part

IP addresses divided into five classes A B C D and E Problems

0 Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network

Any network with more than 255 hosts needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 14: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

14

CPSC 441 Review 40

Addressing in the InternetCIDR Classless InterDomain Routing

subnet portion of address of arbitrary lengthaddress format abcdx where x is bits in subnet portion of addressBefore CIDR Internet used a class-based addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification1 Global decentralized Global

all routers have complete topology link cost infoldquolink staterdquo algorithms

Decentralizedrouter knows about physically-connected neighborsIterative distributed computationsldquodistance vectorrdquo algorithms

2 Static dynamicStatic

routes change slowly over time

Dynamicroutes change more quickly

periodic updatein response to link cost changes

3 Load sensitivityMany Internet routing algos are load insensitive

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 15: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

15

CPSC 441 Review 43

Why Hierarchical Routingscale with 200 million destinations

canrsquot store all destrsquos in routing tablesrouting table exchange would swamp links

administrative autonomyinternet = network of networkseach network admin may want to control routing in its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)routers in same AS run same routing protocol

ldquointra-ASrdquo routingprotocolrouters in different AS can run different intra-AS routing protocol

Gateway routerDirect link to router in another ASEstablishes a ldquopeeringrdquorelationshipPeers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1AS2

1a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm

Intra-AS sets entries for internal destsInter-AS amp Intra-As sets entries for external dests

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 16: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

16

CPSC 441 Review 46

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP tableARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 17: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

17

CPSC 441 Review 49

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accesspoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)traditional Ethernetupstream HFC80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classesChannel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access) allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquoNodes take turns but nodes with more to send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)

Examples of random access MAC protocolsslotted ALOHAALOHACSMA CSMACD CSMACA

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 18: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

18

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timecolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signalsdifficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm1 Adaptor receives

datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mthcollision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential BackoffGoal adapt retransmission attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 19: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

19

CPSC 441 Review 55

CSMACD efficiency

tprop = max prop between 2 nodes in LANttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0Goes to 1 as ttrans goes to infinityMuch better than ALOHA but still decentralized simple and cheap

transprop tt 511efficiency

+=

CPSC 441 Review 56

Switches Routers and HubsHubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward deviceCSMACD at switchMaintains switch tables implement filtering learning algos

Routers are network-layer store-and-forward devices

maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 20: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

20

CPSC 441 Review 58

Wireless Networking Technologies

Mobile devices ndash laptop PDA cellular phone wearable computer hellip

Operating modesInfrastructure mode (Access Point)Ad hoc mode

Access technologyBluetooth (1 Mbps up to 3 meters)IEEE 80211 (up to 55 Mbps 20 ndash 100 meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure modebase station connects mobiles into wired networkhandoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc ModeAd hoc mode

no base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network route among themselves

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 21: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

21

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problemB A hear each otherB C hear each otherA C can not hear each other

means A C unaware of their interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fadingB A hear each otherB C hear each otherA C can not hear each other interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoffinterval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)idea allow sender to ldquoreserverdquo channel rather than random

access of data frames avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to base station using CSMA

RTSs may still collide with each other (but theyrsquore short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodes

sender transmits data frameother stations defer transmissions

Avoid data frame collisions completely using small reservation packets

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 22: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

22

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange

routing tables indicate where each mobile locatedno changes to end-systems

let end-systems handle it indirect routing communication from correspondent to mobile goes through home agent then forwarded to remotedirect routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions ofmobiles

CPSC 441 Review 66

OutlineIntroduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 23: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

23

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristicsTypically delaysensitive

end-to-end delaydelay jitter

But loss tolerant infrequent losses cause minor glitches Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest EffortrdquoInternet

TCPUDPIP no guarantees on delay loss

Todayrsquos multimedia applications implementfunctionality at the app layer to mitigate(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows Fundamental changes in Internet so that apps can reserve end-to-end bandwidthComponents of this architecture are

Admission controlReservation protocolRouting protocolClassifier and route selectionPacket scheduler

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 24: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

24

CPSC 441 Review 70

Concerns with Intserv (24)Scalability signaling maintaining per-flow router state difficult with large number of flows Flexible Service Models Intserv has only two classes Desire ldquoqualitativerdquo service classes

Eg Courier xPress and normal mailEg First business and cattle class

Diffserv approachsimple functions in network core relatively complex functions at edge routers (or hosts)Donrsquot define define service classes provide functional components to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34)

Challenging to stream large files (eg video) from single origin server in real timeSolution replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of timeplacing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long pathsCDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

Page 25: CPSC 441: Review (W06)pages.cpsc.ucalgary.ca/~mahanti/teaching/W06/CPSC441/review.W06.pdf · 3 CPSC 441: Review 7 Internetworks A collection of interconnected networks is called an

25

CPSC 441 Review 73

Finally hellip Examination Format

Technical Terms ndash provide technical terms that best fit a given definition

Eg A field in IPv4 that provides for error detection ndash Checksum

Some short answer questionsEg Compare and contrast datagram networks and virtual circuit networksYou need to only write main pointsAnswer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip