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1-1CS456–ComputerNetworks□Instructor:IanGoldberghttp://www.cs.uwaterloo.ca/~iang/□Classes:TuesdayandTh

ursday8:30–9:50amMC4063(section1)2:30–3:50pmMC2038(section2)□Youwillneedanaccountonthestudent.csenviro

nment.♦Ifyoudon'thaveastudent.csaccountforsomereason,getonesetupinMC3017.1-2CS456–ComputerNetworks□ThiscoursewilluseUW-ACE(akaUWANGEL)ex

tensively.♦Syllabus,calendar,lecturenotes,additionalmaterials,assignments,discussion,communication,importantannouncements,etc.□Itisyourrespon

sibilitytokeepupwiththeinformationonthatsite.♦ButcheckyourUWemailaswell;wemayneedtosendemergencymessagesthere.♦OnlyuseUW-ACEtosendmessagestoc

oursepersonnel.□Feedbackisencouraged!1-3GradingPolicy□Midterm(15%)♦AroundtheendofOctober□Final(35%)□Threeprogrammingassignments(10%+15%+15%)♦Wor

kalone♦RequireCSstudentcomputingenvironmentforsubmission♦AdditionaltasksforCS656students□Twolabs(5%+5%)♦Lab1:InOctober♦Lab2:In

November♦Groupsoftwo□AdditionalresearchsurveypaperforCS656students♦DetailsonUW-ACE□SeeUW-ACEforlateandreappraisalpolicies,acade

micintegritypolicy,andotherdetails.1-4RequiredTextbookComputerNetworking:ATopDownApproachFeaturingtheIntern

et,3rdedition.JimKurose,KeithRossAddison-Wesley,2005.Anoteontheuseofthesepptslides:We’remakingtheseslidesfreelyavailableto

all(faculty,students,readers).They’reinPowerPointformsoyoucanadd,modify,anddeleteslides(includingthisone)andslidecontenttos

uityourneeds.Theyobviouslyrepresentalotofworkonourpart.Inreturnforuse,weonlyaskthefollowing:Ifyouusetheseslides(e.g.,inaclass)insubstantia

llyunalteredform,thatyoumentiontheirsource(afterall,we’dlikepeopletouseourbook!)Ifyoupostanyslidesinsubstantially

unalteredformonawwwsite,thatyounotethattheyareadaptedfrom(orperhapsidenticalto)ourslides,andnoteourcopyrig

htofthismaterial.Thanksandenjoy!JFK/KWRAllmaterialcopyright1996-2006J.FKuroseandK.W.Ross,AllRightsReserved1-5CourseGoals□Learnhowcommunicationn

etworksareputtogether♦mechanisms,algorithms,technologycomponents□OurprimaryexamplewillbetheInternet.♦butwe'lltouch

onsomeothersaswell□Understandfundamentalchallenges□Learnaboutexistingsolutions♦typically:nosingledominantsolution□Whatproblemsstillneedsol

ving?1-6Thisclassandnext□Coursemechanics(done)□Overviewandintroductiontocommunicationsnetworks♦Inparticular,the

Internet1-7Chapter1:IntroductionOurgoal:□get“feel”andterminology□moredepth,detaillaterincourse□approach:♦useInternetasexampleOverview:□what’

stheInternet?□what’saprotocol?□networkedge□networkcore□accessnet,physicalmedia□Internet/ISPstructure

□performance:loss,delay□protocollayers,servicemodels□networkmodeling1-8Chapter1:roadmap1.1WhatistheInternet?1.2Netwo

rkedge1.3Networkcore1.4Networkaccessandphysicalmedia1.5InternetstructureandISPs1.6Delay&lossinpacket-switchednetworks1.7

Protocollayers,servicemodels1.8History1-9What’stheInternet:“nutsandbolts”view□millionsofconnectedcomputingdevices:hosts=endsystems□runningnet

workapps□communicationlinks♦fiber,copper,radio,satellite♦transmissionrate=bandwidth□routers:forwardpackets(chunk

sofdata)localISPcompanynetworkregionalISProuterworkstationservermobile1-10“Cool”internetappliancesWorld’ssmallestwebserverhttp://www-cc

s.cs.umass.edu/~shri/iPic.htmlIPpictureframehttp://www.ceiva.com/Web-enabledtoaster+weatherforecasterInternetphones1-11What’stheI

nternet:aserviceview□Protocolscontrolsending,receivingofmsgs♦e.g.,TCP,IP,HTTP,FTP,PPP□Internet:“networkofnetworks”♦looselyhierarchica

l♦publicInternetversusprivateintranet□Internetstandards♦RFC:Requestforcomments♦IETF:InternetEngineeringTaskForcelo

calISPcompanynetworkregionalISProuterworkstationservermobile1-12What’stheInternet:aserviceview□Communicationinfrastructureena

blesdistributedapplications:♦Web,email,e-commerce,filesharing,games□Communicationservicesprovidedtoappli

cations:♦Connectionlessunreliable♦Connection-orientedreliable1-13What’saprotocol?Humanprotocols:□“What’sthetime?”□“Ihaveaquesti

on”□Introductions□Others?…specificmessagessent…specificactionstakenwhenmessagesreceived,orothereventsNetworkprotocols:□machines

ratherthanhumans□allcommunicationactivityinInternetgovernedbyprotocolsProtocolsdefinetheformatandorderofmessagessentandreceivedamo

ngnetworkentities,andactionstakenonmessagetransmissionandreceipt.1-14ProtocoldiagramsAhumanprotocolandacomp

uternetworkprotocol:HiHiGotthetime?2:00TCPconnectionrequestTCPconnectionresponseGethttp://www.awl.com/kurose-ross<file>time1-15Chapter1:roa

dmap1.1WhatistheInternet?1.2Networkedge1.3Networkcore1.4Networkaccessandphysicalmedia1.5InternetstructureandISPs1.6Delay&

lossinpacket-switchednetworks1.7Protocollayers,servicemodels1.8History1-16Acloserlookatnetworkstructure:□Networkedge:ap

plicationsandhosts□Networkcore:♦routers♦networkofnetworks□Accessnetworks,physicalmedia:communicationlinks1-17Thenetworke

dge:□Endsystems(hosts):♦runapplicationprograms♦e.g.web,email♦at“edgeofnetwork”□Client/servermodel♦clienth

ostrequests,receivesservicefromalways-onserver♦e.g.Webbrowser/server;emailclient/server□Peer-to-peermodel:♦m

inimal(orno)useofdedicatedservers♦e.g.Skype,BitTorrent,KaZaA1-18Networkedge:connection-orientedserviceGoal:datatransferbe

tweenendsystems□handshaking:setup(preparefor)datatransferaheadoftime♦Hello,hellobackhumanprotocol♦set

up“state”intwocommunicatinghosts□TCP-TransmissionControlProtocol♦Internet’sconnection-orientedserviceTCPservice[RFC793]□relia

ble,in-orderbyte-streamdatatransfer♦loss:acknowledgementsandretransmissions□flowcontrol:♦senderwon’toverwhelmreceiver□congestioncontro

l:♦senders“slowdownsendingrate”whennetworkcongested1-19Networkedge:connectionlessserviceGoal:datatransferbetweenendsystems♦sameasbefore!□UDP-UserDat

agramProtocol[RFC768]:♦connectionless♦unreliabledatatransfer♦noflowcontrol♦nocongestioncontrolSomeappsusingTCP:SomeappsusingUDP:♦streamingmedia♦tel

econferencing♦DNS♦Internettelephony♦HTTP(Web)♦FTP(filetransfer)♦ssh(remotelogin)♦SMTP(email)1-20Chapte

r1:roadmap1.1WhatistheInternet?1.2Networkedge1.3Networkcore1.4Networkaccessandphysicalmedia1.5InternetstructureandISPs1.6Delay&l

ossinpacket-switchednetworks1.7Protocollayers,servicemodels1.8History1-21TheNetworkCore□Meshofinterconnect

edrouters□Thefundamentalquestion:howisdatatransferredthroughnet?♦circuit-switching:dedicatedcircuitpercall(e.g.telephonenetwork)♦p

acket-switching:datasentthroughnetindiscrete“chunks”1-22NetworkCore:CircuitSwitchingEnd-to-endresourcesreser

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

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

epieceidleifnotusedbyowningcall(nosharing)□Therearetwocommonwaysofdividinglinkbandwidthinto“pieces”:♦frequencydivision♦timedivisi

on1-24CircuitSwitching:FDMandTDMFDMfrequencytimeTDMfrequencytime4usersExample:1-25Numericalexample□Howlongdoesittaketosendafileof640,000bi

tsfromhostAtohostBoveracircuit-switchednetwork?♦Alllinksare1.536Mbps♦EachlinkusesTDMwith24slots/sec♦500msectoestablishend-to-end

circuitLet’sworkitout!1-26NetworkCore:PacketSwitchingEachend-to-enddatastreamisdividedintopackets□userA,Bpacketssharenetworkresources□eachpacketu

sesfulllinkbandwidth□resourcesusedasneededResourcecontention:□aggregateresourcedemandcanexceedamountavailable□congestion:packetsqueue,wai

tforlinkuse□storeandforward:packetsmoveonehopatatime♦NodereceivescompletepacketbeforeforwardingBandwidthdivisioninto“pieces”De

dicatedallocationResourcereservation1-27PacketSwitching:StatisticalMultiplexingSequenceofA&Bpacketsdoesnothavefixedpattern,sharedondemandstatis

ticalmultiplexing.TDM:eachhostgetssameslotinrevolvingTDMframe.ABC100Mb/sEthernet1.5Mb/sDEstatisticalmultiplexingqueueofpacketsw

aitingforoutputlink1-28Packet-switching:store-and-forward□TakesL/Rsecondstotransmit(pushout)packetofLbi

tsontolinkofRbps□Entirepacketmustarriveatrouterbeforeitcanbetransmittedonnextlink:storeandforward□delay=3L/R(assuming

zeropropagationdelay)Example:□L=7.5Mbits□R=1.5Mbps□delay=15secRRRLmoreondelaynexttime…□3hopsintheroute,sopacketmustbepu

shedout3times1-29Packetswitchingversuscircuitswitching□1Mb/slink□eachuser:♦100kb/swhen“active”♦active10%oftime□circuit-switching:♦

10users□packetswitching:♦with35users,probability>10activeisonly.0004Packetswitchingallowsmoreuserstousethenetwork!Nu

sers1MbpslinkQ:howdidwegetvalue0.0004?1-30Packetswitchingversuscircuitswitching□Greatforburstydata♦resourcesharing♦simp

ler,nocallsetup□Excessivecongestion:packetdelayandloss♦protocolsneededforreliabledatatransfer,congestionc

ontrol□Q:Howtoprovidecircuit-likebehavior?♦bandwidthguaranteesneededforaudio/videoapps♦stillanunsolvedproblem(chapter7)Ispacketswitchinga“slamdunkwi

nner?”1-31Recap□Coursemechanics□WhatistheInternet?♦hosts,routers,communicationlinks♦communicationsservices,protocols□NetworkEdge♦client-server,p

eer-to-peer♦TCP,UDP□NetworkCore♦Circuit-switchednetworks•FDM•TDM♦Packet-switchednetworks1-32Nexttime□Finishintroductionandoverview:♦Networkacces

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