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1-1CS456–ComputerNetworks□Instructor:IanGoldberghttp://www.cs.uwaterloo.ca/~iang/□Classes:TuesdayandThursday8:30–9:50amMC4063(section1)2:30–3:5

0pmMC2038(section2)□Youwillneedanaccountonthestudent.csenvironment.♦Ifyoudon'thaveastudent.csaccountforsomereason,getoneset

upinMC3017.1-2CS456–ComputerNetworks□ThiscoursewilluseUW-ACE(akaUWANGEL)extensively.♦Syllabus,calendar,lecturenotes,additi

onalmaterials,assignments,discussion,communication,importantannouncements,etc.□Itisyourresponsibilitytokeepupwitht

heinformationonthatsite.♦ButcheckyourUWemailaswell;wemayneedtosendemergencymessagesthere.♦OnlyuseUW-ACEtosendme

ssagestocoursepersonnel.□Feedbackisencouraged!1-3GradingPolicy□Midterm(15%)♦AroundtheendofOctober□Fi

nal(35%)□Threeprogrammingassignments(10%+15%+15%)♦Workalone♦RequireCSstudentcomputingenvironmentforsubmission♦AdditionaltasksforCS656students□Twolab

s(5%+5%)♦Lab1:InOctober♦Lab2:InNovember♦Groupsoftwo□AdditionalresearchsurveypaperforCS656students♦DetailsonUW-ACE□SeeUW-

ACEforlateandreappraisalpolicies,academicintegritypolicy,andotherdetails.1-4RequiredTextbookComputerNetworking:ATo

pDownApproachFeaturingtheInternet,3rdedition.JimKurose,KeithRossAddison-Wesley,2005.Anoteontheuseofthesepptslides:We’remakingtheseslidesfreely

availabletoall(faculty,students,readers).They’reinPowerPointformsoyoucanadd,modify,anddeleteslides(includingthisone)andslidecontenttosuityo

urneeds.Theyobviouslyrepresentalotofworkonourpart.Inreturnforuse,weonlyaskthefollowing:Ifyouusetheseslides(e.g.,inaclass)insubst

antiallyunalteredform,thatyoumentiontheirsource(afterall,we’dlikepeopletouseourbook!)Ifyoupostanyslidesinsubstantiallyunaltered

formonawwwsite,thatyounotethattheyareadaptedfrom(orperhapsidenticalto)ourslides,andnoteourcopyrightofthismaterial.Thanksandenjoy!JFK/KWRAllmaterial

copyright1996-2006J.FKuroseandK.W.Ross,AllRightsReserved1-5CourseGoals□Learnhowcommunicationnetworksareputtogether♦mechanisms,algorith

ms,technologycomponents□OurprimaryexamplewillbetheInternet.♦butwe'lltouchonsomeothersaswell□Understandfundamentalchallenges□Learnaboutexis

tingsolutions♦typically:nosingledominantsolution□Whatproblemsstillneedsolving?1-6Thisclassandnext□Coursemechanics(done)□Overviewand

introductiontocommunicationsnetworks♦Inparticular,theInternet1-7Chapter1:IntroductionOurgoal:□get“feel”and

terminology□moredepth,detaillaterincourse□approach:♦useInternetasexampleOverview:□what’stheInternet?□what’saprotocol?□n

etworkedge□networkcore□accessnet,physicalmedia□Internet/ISPstructure□performance:loss,delay□protocol

layers,servicemodels□networkmodeling1-8Chapter1:roadmap1.1WhatistheInternet?1.2Networkedge1.3Networkcore1.4Networkaccessandphysicalmedia1.5

InternetstructureandISPs1.6Delay&lossinpacket-switchednetworks1.7Protocollayers,servicemodels1.8History1-9What’stheInternet:“nu

tsandbolts”view□millionsofconnectedcomputingdevices:hosts=endsystems□runningnetworkapps□communicationlinks♦fiber,copper,radio,satel

lite♦transmissionrate=bandwidth□routers:forwardpackets(chunksofdata)localISPcompanynetworkregionalISProuterworkstationservermobile1-10“Cool”int

ernetappliancesWorld’ssmallestwebserverhttp://www-ccs.cs.umass.edu/~shri/iPic.htmlIPpictureframehttp://www.ceiva.com

/Web-enabledtoaster+weatherforecasterInternetphones1-11What’stheInternet:aserviceview□Protocolscontrolsending,receivingofmsgs♦

e.g.,TCP,IP,HTTP,FTP,PPP□Internet:“networkofnetworks”♦looselyhierarchical♦publicInternetversusprivateintranet□Inte

rnetstandards♦RFC:Requestforcomments♦IETF:InternetEngineeringTaskForcelocalISPcompanynetworkregionalISProuterworkstationservermobile1-

12What’stheInternet:aserviceview□Communicationinfrastructureenablesdistributedapplications:♦Web,email,e-commerce

,filesharing,games□Communicationservicesprovidedtoapplications:♦Connectionlessunreliable♦Connection-orientedreliable1-1

3What’saprotocol?Humanprotocols:□“What’sthetime?”□“Ihaveaquestion”□Introductions□Others?…specificmessagessent…specificactionstakenwhenmessages

received,orothereventsNetworkprotocols:□machinesratherthanhumans□allcommunicationactivityinInternetgovernedbyprotocolsProtocolsdefinetheformatando

rderofmessagessentandreceivedamongnetworkentities,andactionstakenonmessagetransmissionandreceipt.1-1

4ProtocoldiagramsAhumanprotocolandacomputernetworkprotocol:HiHiGotthetime?2:00TCPconnectionrequestTCPc

onnectionresponseGethttp://www.awl.com/kurose-ross<file>time1-15Chapter1:roadmap1.1WhatistheInternet?1.2Networkedge1.3Netwo

rkcore1.4Networkaccessandphysicalmedia1.5InternetstructureandISPs1.6Delay&lossinpacket-switchednetworks1.7Protocollayers,ser

vicemodels1.8History1-16Acloserlookatnetworkstructure:□Networkedge:applicationsandhosts□Networkcore:♦routers♦netw

orkofnetworks□Accessnetworks,physicalmedia:communicationlinks1-17Thenetworkedge:□Endsystems(hosts):♦runapplicationprograms♦e.g

.web,email♦at“edgeofnetwork”□Client/servermodel♦clienthostrequests,receivesservicefromalways-onserver♦e.

g.Webbrowser/server;emailclient/server□Peer-to-peermodel:♦minimal(orno)useofdedicatedservers♦e.g.Skype,BitTorrent,KaZaA1-18Ne

tworkedge:connection-orientedserviceGoal:datatransferbetweenendsystems□handshaking:setup(preparefor)datatransferaheadoftime♦Hello,hel

lobackhumanprotocol♦setup“state”intwocommunicatinghosts□TCP-TransmissionControlProtocol♦Internet’sconnection-orientedserviceTCPservice[RFC793

]□reliable,in-orderbyte-streamdatatransfer♦loss:acknowledgementsandretransmissions□flowcontrol:♦senderwon’toverwhelmreceiver□congest

ioncontrol:♦senders“slowdownsendingrate”whennetworkcongested1-19Networkedge:connectionlessserviceGoal:datatransferbetweenendsystems♦sameasbefore!□U

DP-UserDatagramProtocol[RFC768]:♦connectionless♦unreliabledatatransfer♦noflowcontrol♦nocongestioncontrolSo

meappsusingTCP:SomeappsusingUDP:♦streamingmedia♦teleconferencing♦DNS♦Internettelephony♦HTTP(Web)♦FTP(filetransfer)♦ssh(remotelogin)♦SMTP(email)1

-20Chapter1:roadmap1.1WhatistheInternet?1.2Networkedge1.3Networkcore1.4Networkaccessandphysicalmedia1.5Internetstructure

andISPs1.6Delay&lossinpacket-switchednetworks1.7Protocollayers,servicemodels1.8History1-21TheNetworkCore□

Meshofinterconnectedrouters□Thefundamentalquestion:howisdatatransferredthroughnet?♦circuit-switching:

dedicatedcircuitpercall(e.g.telephonenetwork)♦packet-switching:datasentthroughnetindiscrete“chunks”1-22NetworkCore:CircuitSwitchingE

nd-to-endresourcesreservedfor“call”□linkbandwidth,switchcapacity□dedicatedresources:nosharing□circuit-

like(guaranteed)performance□callsetuprequired1-23NetworkCore:CircuitSwitchingNetworkresources(e.g.,bandwidth)dividedinto“pieces”□

piecesallocatedtocalls□resourcepieceidleifnotusedbyowningcall(nosharing)□Therearetwocommonwaysofdividinglinkbandwi

dthinto“pieces”:♦frequencydivision♦timedivision1-24CircuitSwitching:FDMandTDMFDMfrequencytimeTDMfrequencytime4usersExample:1-25Numericalexa

mple□Howlongdoesittaketosendafileof640,000bitsfromhostAtohostBoveracircuit-switchednetwork?♦Alllinksare1.536Mbps♦EachlinkusesTDMwith

24slots/sec♦500msectoestablishend-to-endcircuitLet’sworkitout!1-26NetworkCore:PacketSwitchingEachend-to-enddatastreamisd

ividedintopackets□userA,Bpacketssharenetworkresources□eachpacketusesfulllinkbandwidth□resourcesuseda

sneededResourcecontention:□aggregateresourcedemandcanexceedamountavailable□congestion:packetsqueue,waitforlinkuse□storeandforward:packetsmoveoneh

opatatime♦NodereceivescompletepacketbeforeforwardingBandwidthdivisioninto“pieces”DedicatedallocationResourcereservation1-27

PacketSwitching:StatisticalMultiplexingSequenceofA&Bpacketsdoesnothavefixedpattern,sharedondemandstatisticalmultiplexing.TDM:eachhostgetssa

meslotinrevolvingTDMframe.ABC100Mb/sEthernet1.5Mb/sDEstatisticalmultiplexingqueueofpacketswaitingforoutputlink1-28Packet-switching:store-and-forwar

d□TakesL/Rsecondstotransmit(pushout)packetofLbitsontolinkofRbps□Entirepacketmustarriveatrouterbeforeitcanbetransmittedonnextlink:

storeandforward□delay=3L/R(assumingzeropropagationdelay)Example:□L=7.5Mbits□R=1.5Mbps□delay=15secRRR

Lmoreondelaynexttime…□3hopsintheroute,sopacketmustbepushedout3times1-29Packetswitchingversuscircuitswitching

□1Mb/slink□eachuser:♦100kb/swhen“active”♦active10%oftime□circuit-switching:♦10users□packetswitching:♦with35users,probability

>10activeisonly.0004Packetswitchingallowsmoreuserstousethenetwork!Nusers1MbpslinkQ:howdidwegetvalue0.0004?1-30Pa

cketswitchingversuscircuitswitching□Greatforburstydata♦resourcesharing♦simpler,nocallsetup□Excessiveconge

stion:packetdelayandloss♦protocolsneededforreliabledatatransfer,congestioncontrol□Q:Howtoprovidecircuit-likebehavior?♦bandwidthguaranteesneed

edforaudio/videoapps♦stillanunsolvedproblem(chapter7)Ispacketswitchinga“slamdunkwinner?”1-31Recap□Coursemechanics□Wha

tistheInternet?♦hosts,routers,communicationlinks♦communicationsservices,protocols□NetworkEdge♦client-server,peer-to-peer♦T

CP,UDP□NetworkCore♦Circuit-switchednetworks•FDM•TDM♦Packet-switchednetworks1-32Nexttime□Finishintroductionandoverview:♦Networkaccessandphysic

almedia♦InternetstructureandISPs♦Delay&lossinpacket-switchednetworks♦Protocollayers,servicemodels