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

)2:30–3:50pmMC2038(section2)□Youwillneedanaccountonthestudent.csenvironment.♦Ifyoudon'thaveastudent.csaccountforso

mereason,getonesetupinMC3017.1-2CS456–ComputerNetworks□ThiscoursewilluseUW-ACE(akaUWANGEL)extensively.♦Syllab

us,calendar,lecturenotes,additionalmaterials,assignments,discussion,communication,importantannouncemen

ts,etc.□Itisyourresponsibilitytokeepupwiththeinformationonthatsite.♦ButcheckyourUWemailaswell;wemayneedtosendemergencymessag

esthere.♦OnlyuseUW-ACEtosendmessagestocoursepersonnel.□Feedbackisencouraged!1-3GradingPolicy□Midterm(15%)♦Aroundtheendof

October□Final(35%)□Threeprogrammingassignments(10%+15%+15%)♦Workalone♦RequireCSstudentcomputingenvironmentforsubmission♦Additionaltasksfor

CS656students□Twolabs(5%+5%)♦Lab1:InOctober♦Lab2:InNovember♦Groupsoftwo□AdditionalresearchsurveypaperforCS656students♦Detail

sonUW-ACE□SeeUW-ACEforlateandreappraisalpolicies,academicintegritypolicy,andotherdetails.1-4RequiredT

extbookComputerNetworking:ATopDownApproachFeaturingtheInternet,3rdedition.JimKurose,KeithRossAddison-Wesley,2005.Anoteontheuse

ofthesepptslides:We’remakingtheseslidesfreelyavailabletoall(faculty,students,readers).They’reinPowerPointformsoyoucanadd,modify,anddeleteslides(in

cludingthisone)andslidecontenttosuityourneeds.Theyobviouslyrepresentalotofworkonourpart.Inreturnforuse,weonlyaskthefollowing:Ifyouuseth

eseslides(e.g.,inaclass)insubstantiallyunalteredform,thatyoumentiontheirsource(afterall,we’dlikepeopletouseourbook!)If

youpostanyslidesinsubstantiallyunalteredformonawwwsite,thatyounotethattheyareadaptedfrom(orperhapsidenticalto)ourslides,andnote

ourcopyrightofthismaterial.Thanksandenjoy!JFK/KWRAllmaterialcopyright1996-2006J.FKuroseandK.W.Ross,AllRights

Reserved1-5CourseGoals□Learnhowcommunicationnetworksareputtogether♦mechanisms,algorithms,technologycomponents□OurprimaryexamplewillbetheInterne

t.♦butwe'lltouchonsomeothersaswell□Understandfundamentalchallenges□Learnaboutexistingsolutions♦typically:nosingledominants

olution□Whatproblemsstillneedsolving?1-6Thisclassandnext□Coursemechanics(done)□Overviewandintroductiontocommunic

ationsnetworks♦Inparticular,theInternet1-7Chapter1:IntroductionOurgoal:□get“feel”andterminology□moredepth,deta

illaterincourse□approach:♦useInternetasexampleOverview:□what’stheInternet?□what’saprotocol?□networkedge□networkcore□accessn

et,physicalmedia□Internet/ISPstructure□performance:loss,delay□protocollayers,servicemodels□networkmodeling1-8Chap

ter1:roadmap1.1WhatistheInternet?1.2Networkedge1.3Networkcore1.4Networkaccessandphysicalmedia1.5InternetstructureandISPs1.6Delay&lossinpacket

-switchednetworks1.7Protocollayers,servicemodels1.8History1-9What’stheInternet:“nutsandbolts”view□milli

onsofconnectedcomputingdevices:hosts=endsystems□runningnetworkapps□communicationlinks♦fiber,copper,radio,satellite♦transmissionrate=bandwidth□routers

:forwardpackets(chunksofdata)localISPcompanynetworkregionalISProuterworkstationservermobile1-10“Cool”internetappliancesWorld’ssmallest

webserverhttp://www-ccs.cs.umass.edu/~shri/iPic.htmlIPpictureframehttp://www.ceiva.com/Web-enabledtoaster+weatherforecasterInternetphones1-1

1What’stheInternet:aserviceview□Protocolscontrolsending,receivingofmsgs♦e.g.,TCP,IP,HTTP,FTP,PPP□Internet:“networkofnetworks”♦looselyhierar

chical♦publicInternetversusprivateintranet□Internetstandards♦RFC:Requestforcomments♦IETF:InternetEngineeringTaskForcelocalISP

companynetworkregionalISProuterworkstationservermobile1-12What’stheInternet:aserviceview□Communicationinfrastructureenablesdistribute

dapplications:♦Web,email,e-commerce,filesharing,games□Communicationservicesprovidedtoapplications:♦Connectionlessunreliable♦Connection-orientedr

eliable1-13What’saprotocol?Humanprotocols:□“What’sthetime?”□“Ihaveaquestion”□Introductions□Others?…specificmessagessent…specificactionstake

nwhenmessagesreceived,orothereventsNetworkprotocols:□machinesratherthanhumans□allcommunicationactivityinInternetgovernedbyp

rotocolsProtocolsdefinetheformatandorderofmessagessentandreceivedamongnetworkentities,andactionstakenonmessagetran

smissionandreceipt.1-14ProtocoldiagramsAhumanprotocolandacomputernetworkprotocol:HiHiGotthetime?2:00TCPconnectionreques

tTCPconnectionresponseGethttp://www.awl.com/kurose-ross<file>time1-15Chapter1:roadmap1.1WhatistheInternet?1.2Networkedge1.3Networkcore1.4Networkacce

ssandphysicalmedia1.5InternetstructureandISPs1.6Delay&lossinpacket-switchednetworks1.7Protocollayers,servicemodels

1.8History1-16Acloserlookatnetworkstructure:□Networkedge:applicationsandhosts□Networkcore:♦routers♦networkofnetworks□Accessnet

works,physicalmedia:communicationlinks1-17Thenetworkedge:□Endsystems(hosts):♦runapplicationprograms♦e.g.web,email♦at“edg

eofnetwork”□Client/servermodel♦clienthostrequests,receivesservicefromalways-onserver♦e.g.Webbrowser/server;emailclient/server□Peer-to

-peermodel:♦minimal(orno)useofdedicatedservers♦e.g.Skype,BitTorrent,KaZaA1-18Networkedge:connection-orientedserviceGoal:datatransferbetwe

enendsystems□handshaking:setup(preparefor)datatransferaheadoftime♦Hello,hellobackhumanprotocol♦setup“state”intwocommunicat

inghosts□TCP-TransmissionControlProtocol♦Internet’sconnection-orientedserviceTCPservice[RFC793]□reliable,in-orderbyte-streamdatatransfer

♦loss:acknowledgementsandretransmissions□flowcontrol:♦senderwon’toverwhelmreceiver□congestioncontrol:♦senders“slowdownsendingrate”whennetworkc

ongested1-19Networkedge:connectionlessserviceGoal:datatransferbetweenendsystems♦sameasbefore!□UDP-UserDatagramProtocol[RFC768]:♦connectionless

♦unreliabledatatransfer♦noflowcontrol♦nocongestioncontrolSomeappsusingTCP:SomeappsusingUDP:♦streamingmedia♦teleconferencing♦DNS♦Internett

elephony♦HTTP(Web)♦FTP(filetransfer)♦ssh(remotelogin)♦SMTP(email)1-20Chapter1:roadmap1.1WhatistheInternet?1.2Networkedge1.3Networkcore1.4Networkac

cessandphysicalmedia1.5InternetstructureandISPs1.6Delay&lossinpacket-switchednetworks1.7Protocollayers,servicemodels1.8History1-21TheNetworkCore□Me

shofinterconnectedrouters□Thefundamentalquestion:howisdatatransferredthroughnet?♦circuit-switching:dedicatedcircuitper

call(e.g.telephonenetwork)♦packet-switching:datasentthroughnetindiscrete“chunks”1-22NetworkCore:CircuitSwitchingEnd-to-endresourcesre

servedfor“call”□linkbandwidth,switchcapacity□dedicatedresources:nosharing□circuit-like(guaranteed)performance□c

allsetuprequired1-23NetworkCore:CircuitSwitchingNetworkresources(e.g.,bandwidth)dividedinto“pieces”□piecesallocatedtocalls□resourcepieceid

leifnotusedbyowningcall(nosharing)□Therearetwocommonwaysofdividinglinkbandwidthinto“pieces”:♦frequencydivision

♦timedivision1-24CircuitSwitching:FDMandTDMFDMfrequencytimeTDMfrequencytime4usersExample:1-25Numerical

example□Howlongdoesittaketosendafileof640,000bitsfromhostAtohostBoveracircuit-switchednetwork?♦Alllinksare1.536Mbps♦EachlinkusesTDM

with24slots/sec♦500msectoestablishend-to-endcircuitLet’sworkitout!1-26NetworkCore:PacketSwitchingEachend-to-enddatastreamisdividedintopackets□u

serA,Bpacketssharenetworkresources□eachpacketusesfulllinkbandwidth□resourcesusedasneededResourcecontent

ion:□aggregateresourcedemandcanexceedamountavailable□congestion:packetsqueue,waitforlinkuse□storeandfo

rward:packetsmoveonehopatatime♦NodereceivescompletepacketbeforeforwardingBandwidthdivisioninto“pieces”DedicatedallocationR

esourcereservation1-27PacketSwitching:StatisticalMultiplexingSequenceofA&Bpacketsdoesnothavefixedpattern,

sharedondemandstatisticalmultiplexing.TDM:eachhostgetssameslotinrevolvingTDMframe.ABC100Mb/sEthernet1.5Mb/sDEstatisticalmultiplexingqueueofpacke

tswaitingforoutputlink1-28Packet-switching:store-and-forward□TakesL/Rsecondstotransmit(pushout)packetofLbitsontolinkofRbps□Entire

packetmustarriveatrouterbeforeitcanbetransmittedonnextlink:storeandforward□delay=3L/R(assumingzeropropagationdelay)Exam

ple:□L=7.5Mbits□R=1.5Mbps□delay=15secRRRLmoreondelaynexttime…□3hopsintheroute,sopacketmustbepushedout3times1-29Packetswitchi

ngversuscircuitswitching□1Mb/slink□eachuser:♦100kb/swhen“active”♦active10%oftime□circuit-switching:♦10users□p

acketswitching:♦with35users,probability>10activeisonly.0004Packetswitchingallowsmoreuserstousethenetwork!Nusers1MbpslinkQ:howdidwegetvalue0.0004?1-

30Packetswitchingversuscircuitswitching□Greatforburstydata♦resourcesharing♦simpler,nocallsetup□Excessivecongestion:packetdelayandlos

s♦protocolsneededforreliabledatatransfer,congestioncontrol□Q:Howtoprovidecircuit-likebehavior?♦bandwidthguaranteesneeded

foraudio/videoapps♦stillanunsolvedproblem(chapter7)Ispacketswitchinga“slamdunkwinner?”1-31Recap□Coursemechani

cs□WhatistheInternet?♦hosts,routers,communicationlinks♦communicationsservices,protocols□NetworkEdge♦client-server,peer-to-peer

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

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