計(jì)算機(jī)網(wǎng)絡(luò)全部課件chapter 1 v6

Introduction1-1Chapter1

IntroductionComputerNetworking:ATopDownApproach

6thedition

JimKurose,KeithRoss

Addison-Wesley

March2012Anoteontheuseofthesepptslides:We’remakingtheseslidesfreelyavailabletoall(faculty,students,readers).They’reinPowerPointformsoyouseetheanimations;andcanadd,modify,anddeleteslides(includingthisone)andslidecontenttosuityourneeds.Theyobviouslyrepresentalotofworkonourpart.Inreturnforuse,weonlyaskthefollowing:Ifyouusetheseslides(e.g.,inaclass)thatyoumentiontheirsource(afterall,we’dlikepeopletouseourbook!)Ifyoupostanyslidesonawwwsite,thatyounotethattheyareadaptedfrom(orperhapsidenticalto)ourslides,andnoteourcopyrightofthismaterial.Thanksandenjoy!JFK/KWRAllmaterialcopyright1996-2012J.FKuroseandK.W.Ross,AllRightsReservedIntroductionChapter1:introductionourgoal:

get“feel”andterminologymoredepth,detaillaterincourseapproach:useInternetasexampleoverview:what’stheInternet?what’saprotocol?courseintroductionnetworkedge;hosts,accessnet,physicalmedianetworkcore:packet/circuitswitching,Internetstructureperformance:loss,delay,throughputsecurityprotocollayers,servicemodelshistory1-2IntroductionChapter1:roadmap1.1whatistheInternet?1.2networkedge

endsystems,accessnetworks,links1.3networkcorepacketswitching,circuitswitching,networkstructure1.4delay,loss,throughputinnetworks1.5protocollayers,servicemodels1.6networksunderattack:security1.7history1-3IntroductionNetwork：what1-4IntroductionNetwork：what1-5IntroductionNetwork：what1-6IntroductionNetwork：what1-7Graphwithnodesandlinks由節(jié)點(diǎn)和連線構(gòu)成的圖，表示研究諸對(duì)象及其相互聯(lián)系IntroductionNetwork：How1-8statistics

throughput,utilizationratio

Ifthereareptelephonecallsintime?t，andwhatistheprobabilityofxcallsintimet?Solution:wecandividetintonparts,andthen

Network：Howstatistics

throughput,utilizationratioexample1暑期補(bǔ)課期間，每天中午就餐時(shí)間段，公交中科大西站候車人數(shù)服從參數(shù)為λ的泊松分布,假設(shè)λ=5.2,已知我們班有一位同學(xué)在那里候車,求這車站就他一人候車的概率是？exampl2結(jié)合example1，假設(shè)學(xué)生均乘坐180路公交到文星餐廳就餐，該公交座位數(shù)為20，允許超載50%，平均每10分鐘一班，則平均每位同學(xué)等車時(shí)間是多久？

請(qǐng)?jiān)O(shè)計(jì)一個(gè)低成本、高效率的公交運(yùn)營(yíng)方案。IntroductionNetwork：How1-10statisticsExponentialdistribution–mostcommonlyusedastheinter-arrivaltime/servicetimedistributionProbabilitydensityfunction(pdf):Cumulativedensityfunction(cdf):Mean,variance,standarddeviationIntroductionNetwork：How1-11statistics

throughput,utilizationratio

solve

differentialequationsschedule

congresscontrolgraphtheory

shortestpathalgorithm...IntroductionNetwork：How1-12Synchronousbasicclock,propagationdelayServicetransport,communicationsSecurity

correct,protected...Andotherproblems……ConclusionSocalledcomputernetworksamunicationsnetworkwhichallowscomputerstoexchangedata.Networkedcomputingdevicespassdatatoeachotheralongnetworklinks(dataconnections).IntroductionWhat’stheInternet:“nutsandbolts”viewmillionsofconnectedcomputingdevices:hosts=endsystems

runningnetworkappscommunicationlinksfiber,copper,radio,satellitetransmissionrate:bandwidthPacketswitches:forwardpackets(chunksofdata)routersandswitcheswiredlinkswirelesslinksroutermobilenetworkglobalISPregionalISPhomenetworkinstitutionalnetworksmartphonePCserverwirelesslaptop1-14Introduction“Fun”internetappliancesIPpictureframe

Web-enabledtoaster+weatherforecasterInternetphonesInternetrefrigeratorSlingbox:watch,controlcableTVremotely1-15Tweet-a-watt:monitorenergyuseIntroductionInternet:“networkofnetworks”InterconnectedISPsprotocolscontrolsending,receivingofmsgse.g.,TCP,IP,HTTP,Skype,802.11InternetstandardsRFC:RequestforcommentsIETF:InternetEngineeringTaskForce

What’stheInternet:“nutsandbolts”viewmobilenetworkglobalISPregionalISPhomenetworkinstitutionalnetwork1-16What’stheInternet:aserviceviewInfrastructurethatprovidesservicestoapplications:Web,VoIP,email,games,merce,socialnets,…providesprogramminginterfacetoappshooksthatallowsendingandreceivingappprogramsto“connect”toInternetprovidesserviceoptions,analogoustopostalservicemobilenetworkglobalISPregionalISPhomenetworkinstitutionalnetworkIntroduction1-17IntroductionWhat’saprotocol?humanprotocols:“what’sthetime?”“Ihaveaquestion”introductions…specificmsgssent…specificactionstakenwhenmsgsreceived,orothereventsnetworkprotocols:machinesratherthanhumansallcommunicationactivityinInternetgovernedbyprotocolsprotocolsdefineformat,orderofmsgssentandreceivedamongnetworkentities,andactionstakenonmsgtransmission,receipt

1-18Introductionahumanprotocolandacomputernetworkprotocol:Q:otherhumanprotocols?HiHiGotthetime?2:00TCPconnectionresponseGet<file>timeTCPconnectionrequestWhat’saprotocol?1-19IntroductionChapter1:hyperlinkCourseintroductionofsummer20151-20IntroductionChapter1:roadmap1.1whatistheInternet?1.2networkedge

endsystems,accessnetworks,links1.3networkcorepacketswitching,circuitswitching,networkstructure1.4delay,loss,throughputinnetworks1.5protocollayers,servicemodels1.6networksunderattack:security1.7history1-21IntroductionAcloserlookatnetworkstructure:networkedge:hosts:clientsandserversserversoftenindatacentersaccessnetworks,physicalmedia:wired,wirelesscommunicationlinks

networkcore:interconnectedroutersnetworkofnetworksmobilenetworkglobalISPregionalISPhomenetworkinstitutionalnetwork1-22IntroductionAccessnetworksandphysicalmediaQ:Howtoconnectendsystemstoedgerouter?residentialaccessnetsinstitutionalaccessnetworks(school,company)mobileaccessnetworkskeepinmind:bandwidth(bitspersecond)ofaccessnetwork?sharedordedicated?1-23IntroductionAccessnet:digitalsubscriberline(DSL)centralofficeISPtelephonenetworkDSLAMvoice,datatransmittedatdifferentfrequenciesoverdedicatedlinetocentralofficeuseexistingtelephonelinetocentralofficeDSLAMdataoverDSLphonelinegoestoInternetvoiceoverDSLphonelinegoestotelephonenet<2.5Mbpsupstreamtransmissionrate(typically<1Mbps)<24Mbpsdownstreamtransmissionrate(typically<10Mbps)DSLmodemsplitterDSLaccessmultiplexer1-24DMT（DiscreteMulti-Tone）…SpectrumFreq.Uplinktelephone04Downlink…(kHz)~40~138~11001-25IntroductionDMT

andDTMFDMTakindofFSKtechnologyDTMF（Dual

Tone

Multi

Frequency）1-26IntroductionIntroductionAccessnet:cablenetworkcablemodemsplitter…cableheadendChannelsVIDEOVIDEOVIDEOVIDEOVIDEOVIDEODATADATACONTROL123456789frequencydivisionmultiplexing:differentchannelstransmittedindifferentfrequencybands1-27Introductiondata,TVtransmittedatdifferentfrequenciesoversharedcabledistributionnetworkcablemodemsplitter…cableheadendCMTSISPcablemodemterminationsystemHFC:hybridfibercoaxasymmetric:upto30Mbpsdownstreamtransmissionrate,2Mbpsupstreamtransmissionratenetworkofcable,fiberattacheshomestoISProuterhomesshareaccessnetwork

tocableheadendunlikeDSL,whichhasdedicatedaccesstocentralofficeAccessnet:cablenetwork1-28SpectrumofHFCDownlinkUplink540505507501000OriginalAnalogyTVDigitalSignalFreq.(MHz)Reserved1-29IntroductionCableModemsTypicaldetailsoftheupstreamanddownstreamchannelsinNorthAmerica.機(jī)頂盒(set-topbox)Introduction1-30IntroductionAccessnet:homenetworkto/fromheadendorcentralofficecableorDSLmodemrouter,firewall,NATwiredEthernet(100Mbps)wirelessaccesspoint(54Mbps)wirelessdevicesoftencombinedinsinglebox1-31IntroductionEnterpriseaccessnetworks(Ethernet)typicallyusedincompanies,universities,etc10Mbps,100Mbps,1Gbps,10Gbpstransmissionratestoday,endsystemstypicallyconnectintoEthernetswitchEthernetswitchinstitutionalmail,webserversinstitutionalrouterinstitutionallinktoISP(Internet)1-32USTCsz’Wirelessaccessnetworkssharedwirelessaccessnetworkconnectsendsystemtorouterviabasestationaka“accesspoint”wirelessLANs:withinbuilding(100ft)802.11b/g(WiFi):11,54Mbpstransmissionratewide-areawirelessaccessprovidedbytelco(cellular)operator,10’skmbetween1and10Mbps3G,4G:LTEtoInternettoInternet1-34Wirelessaccessnetworkssharedwirelessaccessnetworkconnectsendsystemtorouter1-35Host:sendspacketsofdatahostsendingfunction:takesapplicationmessagebreaksintosmallerchunks,knownaspackets,oflengthLbitstransmitspacketintoaccessnetworkattransmissionrateRlinktransmissionrate,akalinkcapacity,akalinkbandwidthR:linktransmissionratehost12twopackets,LbitseachpackettransmissiondelaytimeneededtotransmitL-bitpacketintolinkL(bits)R(bits/sec)==1-36IntroductionPhysicalmediabit:

propagatesbetween

transmitter/receiverpairsphysicallink:whatliesbetweentransmitter&receiverguidedmedia:signalspropagateinsolidmedia:copper,fiber,coaxunguidedmedia:

signalspropagatefreely,e.g.,radiotwistedpair(TP)twoinsulatedcopperwiresCategory5:100Mbps,1GpbsEthernetCategory6:10Gbps1-37IntroductionDiscuss：Inter-SymbolInterference碼間串?dāng)_aformof

distortion

ofa

signal

inwhichone

symbol

interfereswithsubsequentsymbolsMultipathpropagationBandlimitedchannelsPowerloss，crosstalk1-38Howtodeterminethemedia’sbandwidth？IntroductionDiscuss：Inter-SymbolInterference碼間串?dāng)_aformof

distortion

ofa

signal

inwhichone

symbol

interfereswithsubsequentsymbolsMultipathpropagationBandlimitedchannelseyepatternsfortestISI1-39Howtodeterminethemedia’sbandwidth？IntroductionDiscuss：Shannon'sTheoremShannon'sTheoremgivesanupperboundtothecapacityofalink,inbitspersecond(bps),asafunctionoftheavailablebandwidthandthesignal-to-noiseratioofthelink.TheTheoremcanbestatedas:C=B*log2(1+S/N)whereCistheachievablechannelcapacity,Bisthebandwidthoftheline,SistheaveragesignalpowerandNistheaveragenoisepower.example:Foratypicaltelephonelinewithasignal-to-noiseratioof30dBandanaudiobandwidthof3kHz,wegetamaximumdatarateof:C=3000*log2(1001)whichisalittlelessthan30kbps.1-40Howtodeterminethemedia’sbandwidth？PhysicalGuidedMedia1-41IntroductionIntroductionPhysicalmedia:coax,fibercoaxialcable:twoconcentriccopperconductorsbidirectionalbroadband:multiplechannelsoncableHFCfiberopticcable:glassfibercarryinglightpulses,eachpulseabithigh-speedoperation:high-speedpoint-to-pointtransmission(e.g.,10’s-100’sGpbstransmissionrate)lowerrorrate:repeatersspacedfarapartimmunetoelectromagneticnoise1-42PhysicalGuidedMedia1-43IntroductionBNCconnectorfibercoaxialcableIntroductionPhysicalmedia:radiosignalcarriedinelectromagneticspectrumnophysical“wire”bidirectionalpropagationenvironmenteffects:reflectionobstructionbyobjectsinterferenceradiolinktypes:terrestrialmicrowavee.g.upto45MbpschannelsLAN(e.g.,WiFi)11Mbps,54Mbpswide-area(e.g.,cellular)3Gcellular:~fewMbpssatelliteKbpsto45Mbpschannel(ormultiplesmallerchannels)270msecend-enddelaygeosynchronousversuslowaltitude1-44IntroductionChapter1:roadmap1.1whatistheInternet?1.2networkedge

endsystems,accessnetworks,links1.3networkcorepacketswitching,circuitswitching,networkstructure1.4delay,loss,throughputinnetworks1.5protocollayers,servicemodels1.6networksunderattack:security1.7history1-45Introductionmeshofinterconnectedrouterspacket-switching:hostsbreakapplication-layermessagesintopacketsforwardpackets

fromoneroutertothenext,acrosslinksonpathfromsourcetodestinationeachpackettransmittedatfulllinkcapacityThenetworkcore1-46IntroductionPacket-switching:store-and-forwardtakesL/Rsecondstotransmit(pushout)L-bitpacketintolinkatRbpsstoreandforward:

entirepacketmustarriveatrouterbeforeitcanbetransmittedonnextlinkone-hopnumericalexample:L=7.5MbitsR=1.5Mbpsone-hoptransmissiondelay=5secmoreondelayshortly…1-47sourceRbpsdestination123LbitsperpacketRbpsend-enddelay=2L/R(assumingzeropropagationdelay)IntroductionPacketSwitching:queuingdelay,lossABCR=100Mb/sR=1.5Mb/sDEqueueofpacketswaitingforoutputlink1-48queuingandloss:Ifarrivalrate(inbits)tolinkexceedstransmissionrateoflinkforaperiodoftime:packetswillqueue,waittobetransmittedonlinkpacketscanbedropped(lost)ifmemory(buffer)fillsupIntroductionPacketSwitching:queuingdelay,loss1-49ABasicQueueSetupIntroductionPacketSwitching:queuingdelay,loss1-50Elrangdistibution(Gammadistribution)LetT1,T2…TkbeindependentexponentialdistributionwithparameterλT=T1+T2+…+Tk,TfollowsElrangdistributionProbabilitydensityfunction:Mean,varianceK=1->exponentialdistributionWhenkissuitablylarge->normaldistributionIntroductionPacketSwitching:queuingdelay,loss1-51Elrangdistibution(Gammadistribution)K=1->exponentialdistributionWhenkissuitablylarge->normaldistributionNetworkLayer4-52Twokeynetwork-corefunctionsforwarding:

movepacketsfromrouter’sinputtoappropriaterouteroutputrouting:

determinessource-destinationroutetakenbypacketsroutingalgorithmsroutingalgorithmlocalforwardingtableheadervalueoutputlink010001010111100132211230111destaddressinarrivingpacket’sheaderTryyourself：routetableIntroductionAlternativecore:circuitswitchingend-endresourcesallocatedto,reservedfor“call”betweensource&dest:Indiagram,eachlinkhasfourcircuits.callgets2ndcircuitintoplinkand1stcircuitinrightlink.dedicatedresources:nosharingcircuit-like(guaranteed)performancecircuitsegmentidleifnotusedbycall(nosharing)Commonlyusedintraditionaltelephonenetworks1-54IntroductionCircuitswitching:FDMversusTDMFDMfrequencytimeTDMfrequencytime4usersExample:1-55IntroductionPacketswitchingversuscircuitswitchingexample:1Mb/slinkeachuser:100kb/swhen“active”active10%oftimecircuit-switching:

10userspacketswitching:

with35users,probability>10activeatsametimeislessthan.0004*packetswitchingallowsmoreuserstousenetwork!N

users1MbpslinkQ:howdidwegetvalue0.0004?Q:whathappensif>35users?…..1-56*CheckouttheonlineinteractiveexercisesformoreexamplesIntroductiongreatforburstydataresourcesharingsimpler,nocallsetupexcessivecongestionpossible:packetdelayandlossprotocolsneededforreliabledatatransfer,congestioncontrolQ:Howtoprovidecircuit-likebehavior?bandwidthguaranteesneededforaudio/videoappsstillanunsolvedproblem(chapter7)ispacketswitchinga“slamdunkwinner?”Q:humananalogiesofreservedresources(circuitswitching)versuson-demandallocation(packet-switching)?Packetswitchingversuscircuitswitching1-57IntroductionSeetheflashdemonstrationPacketswitchingversuscircuitswitching1-58Internetstructure:networkofnetworksEndsystemsconnecttoInternetviaaccessISPs(InternetServiceProviders)Residential,companyanduniversityISPsAccessISPsinturnmustbeinterconnected.SothatanytwohostscansendpacketstoeachotherResultingnetworkofnetworksisverycomplexEvolutionwasdrivenbyeconomicsandnationalpoliciesLet’stakeastepwiseapproachtodescribecurrentInternetstructureInternetstructure:networkofnetworksQuestion:givenmillionsofaccessISPs,howtoconnectthemtogether?accessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnet………………Internetstructure:networkofnetworksOption:connecteachaccessISPtoeveryotheraccessISP?accessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnet……………………………connectingeachaccessISPtoeachotherdirectlydoesn’tscale:O(N2)connections.Internetstructure:networkofnetworksaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnet………………Option:connecteachaccessISPtoaglobaltransitISP?CustomerandproviderISPshaveeconomicagreement.global

ISPInternetstructure:networkofnetworksaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnet………………ButifoneglobalISPisviablebusiness,therewillbecompetitors….ISPBISPAISPCInternetstructure:networkofnetworksaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnet………………ButifoneglobalISPisviablebusiness,therewillbecompetitors….whichmustbeinterconnectedISPBISPAISPCIXPIXPpeeringlinkInternetexchangepointInternetstructure:networkofnetworksaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnet…………………andregionalnetworksmayarisetoconnectaccessnetstoISPSISPBISPAISPCIXPIXPregionalnetInternetstructure:networkofnetworksaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnetaccessnet…………………andcontentprovidernetworks(e.g.,Google,Microsoft,Akamai)mayruntheirownnetwork,tobringservices,contentclosetoendusersISPBISPAISPBIXPIXPregionalnetContentprovidernetworkIntroductionInternetstructure:networkofnetworksatcenter:small#ofwell-connectedlargenetworks“tier-1”commercialISPs

(e.g.,Level3,Sprint,AT&T,NTT),national&internationalcoveragecontentprovidernetwork(e.g,Google):privatenetworkthatconnectsitdatacenterstoInternet,oftenbypassingtier-1,regionalISPs1-67accessISPaccessISPaccessISPaccessISPaccessISPaccessISPaccessISPaccessISPRegionalISPRegionalISPIXPIXPTier1ISPTier1ISPGoogleIXPIntroductionTier-1ISP:e.g.,Sprint…to/fromcustomerspeering

to/frombackbone…………POP:point-of-presence1-68IntroductionChapter1:roadmap1.1whatistheInternet?1.2networkedge

endsystems,accessnetworks,links1.3networkcore

packetswitching,circuitswitching,networkstructure1.4delay,loss,throughputinnetworks1.5protocollayers,servicemodels1.6networksunderattack:security1.7history1-69IntroductionHowdolossanddelayoccur?packetsqueueinrouterbuffers

packetarrivalratetolink(temporarily)exceedsoutputlinkcapacitypacketsqueue,waitforturnABpacketbeingtransmitted(delay)packetsqueueing

(delay)free(available)buffers:arrivingpacketsdropped(loss)ifnofreebuffers1-70IntroductionFoursourcesofpacketdelaydproc:nodalprocessing

checkbiterrorsdetermineoutputlinktypically<msecABpropagationtransmissionnodalprocessingqueueing

dqueue:queueingdelaytimewaitingatoutputlinkfortransmissiondependsoncongestionlevelofrouterdnodal=dproc+dqueue+dtrans+dprop1-71Introductiondtrans:transmissiondelay:L:packetlength(bits)R:linkbandwidth(bps)dtrans

=L/Rdprop:propagationdelay:d:lengthofphysicallinks:propagationspeedinmedium(~2x108m/sec)dprop=d/sdtransanddpropverydifferentFoursourcesofpacketdelaypropagationnodalprocessingqueueingdnodal=dproc+dqueue+dtrans+dprop1-72ABtransmission*CheckouttheJavaappletforaninteractiveanimationontransvs.propdelayIntroductionCaravananalogycars“propagate”at

100km/hrtollboothtakes12sectoservicecar(bittransmissiontime)car~bit;caravan~packetQ:Howlonguntilcaravanislinedupbefore2ndtollbooth?timeto“push”entirecaravanthroughtollboothontohighway=12*10=120sectimeforlastcartopropagatefrom1stto2ndtollboth:100km/(100km/hr)=1hrA:62minutestollboothtollboothten-carcaravan100km100km1-73IntroductionCaravananalogy(more)supposecarsnow“propagate”at1000km/hrandsupposetollboothnowtakesonemintoserviceacarQ:Willcarsarriveto2ndboothbeforeallcarsservicedatfirstbooth?A:Yes!after7min,1stcararrivesatsecondbooth;threecarsstillat1stbooth.tollboothtollboothten-carcaravan100km100km1-74IntroductionR:linkbandwidth(bps)L:packetlength(bits)a:averagepacketarrivalratetrafficintensity=La/RLa/R~0:avg.queueingdelaysmallLa/R->1:avg.queueingdelaylargeLa/R>1:more“work”arrivingthancanbeserviced,averagedelayinfinite!averagequeueingdelayLa/R~0Queueingdelay(revisited)La/R->11-75*CheckouttheJavaappletforaninteractiveanimationonqueuingandlossIntroduction“Real”Internetdelaysandrouteswhatdo“real”Internetdelay&losslooklike?tracerouteprogram:providesdelaymeasurementfromsourcetorouteralongend-endInternetpathtowardsdestination.Foralli:sendsthreepacketsthatwillreachrouterionpathtowardsdestinationrouteriwillreturnpacketstosendersendertimesintervalbetweentransmissionandreply.3probes3probes3probes1-76Introduction“Real”Internetdelays,routes1cs-gw(54)1ms1ms2ms2(45)1ms1ms2ms3(30)6ms5ms5ms4(29)16ms11ms13ms5(36)21ms18ms18ms6()22ms18ms22ms7(6)22ms22ms22ms853(53)104ms109ms106ms9(29)109ms102ms104ms10(0)113ms121ms114ms11(4)112ms114ms112ms12nio-n2.cssi.renater.fr(3)111ms114ms116ms13nice.cssi.renater.fr(02)123ms125ms124ms14r3t2-nice.cssi.renater.fr(10)126ms126ms124ms15(4)135ms128ms133ms165(5)126ms128ms126ms17***18***19.fr(42)132ms128ms136mstraceroute:to3delaymeasurementsfromto*meansnoresponse(probelost,routernotreplying)trans-oceaniclink1-77*DosometraceroutesfromexoticcountriesatexampleIntroductionPacketlossqueue(akabuffer)precedinglinkinbufferhasfinitecapacitypacketarrivingtofullqueuedropped(akalost)lostpacketmayberetransmittedbypreviousnode,bysourceendsystem,ornotatallABpacketbeingtransmittedpacketarrivingtofullbufferislostbuffer(waitingarea)1-79*CheckouttheJavaappletforaninteractiveanimationonqueuingandlossIntroductionThroughputthroughput:rate(bits/timeunit)atwhichbitstransferredbetweensender/receiverinstantaneous:rateatgivenpointintimeaverage:rateoverlongerperiodoftimeserver,withfileofFbitstosendtoclientlinkcapacityRs

bits/seclinkcapacityRc

bits/secserversendsbits(fluid)intopipe

pipethatcancarryfluidatrateRs

bits/sec)

pipethatcancarryfluidatrateRc

bits/sec)1-80IntroductionThroughput(more)Rs<Rc

Whatisaverageend-endthroughput?

Rs

bits/secRc

bits/secRs>Rc

Whatisaverageend-endthroughput?linkonend-endpaththatconstrainsend-endthroughputbottlenecklinkRs

bits/sec

Rc

bits/sec1-81IntroductionThroughput:Internetscenario10connections(fairly)sharebackbonebottlenecklinkR

bits/secRsRsRsRcRcRcRper-connectionend-endthroughput:min(Rc,Rs,R/10)inpractice:RcorRsisoftenbottleneck1-82IntroductionChapter1:roadmap1.1whatistheInternet?1.2networkedge

endsystems,accessnetworks,links1.3networkcore

packetswitching,circuitswitching,networkstructure1.4delay,loss,throughputinnetworks1.5protocollayers,servicemodels1.6networksunderattack:security1.7history1-83IntroductionProtocol“l(fā)ayers”Networksarecomplex,withmany“pieces”:hostsrouterslinksofvariousmediaapplicationsprotocolshardware,softwareQuestion:

isthereanyhopeoforganizingstructureofnetwork?….oratleastourdiscussionofnetworks?1-84IntroductionOrganizationofairtravelaseriesofstepsticket(purchase)baggage(check)gates(load)runwaytakeoffairplaneroutingticket(complain)baggage(claim)gates(unload)runwaylandingairplaneroutingairplanerouting1-85Introductionticket(purchase)baggage(check)gates(load)runway(takeoff)airplaneroutingdepartureairportarrivalairportintermediateair-trafficcontrolcentersairplaneroutingairplaneroutingticket(complain)baggage(claimgates(unload)runway(land)airplaneroutingticketbaggagegatetakeoff/landingairplaneroutingLayeringofairlinefunctionalitylayers:

eachlayerimplementsaserviceviaitsowninternal-layeractionsrelyingonservicesprovidedbylayerbelow1-86IntroductionWhylayering?dealingwithcomplexsystems:explicitstructureallowsidentification,relationshipofcomplexsystem’spieceslayeredreferencemodelfordiscussionmodularizationeasesmaintenance,updatingofsystemchangeofimplementationoflayer’sservicetransparenttorestofsysteme.g.,changeingateproceduredoesn’taffectrestofsystemlayeringconsideredharmful?1-87IntroductionInternetprotoco