计算机网络自定向下设计课件第11章VIP专享VIP免费

NetworkLayerGoals:•understandprinciplesbehindnetworklayerservices:–routing(pathselection)–dealingwithscale–howarouterworks–advancedtopics:IPv6,multicast•instantiationandimplementationintheInternetOverview:•networklayerservices•routingprinciple:pathselection•hierarchicalrouting•IP•Internetroutingprotocolsreliabletransfer–intra-domain–inter-domain•what’sinsidearouter?•IPv6•multicastroutingNetworklayerfunctions•transportpacketfromsendingtoreceivinghosts•networklayerprotocolsineveryhost,routerthreeimportantfunctions:•pathdetermination:routetakenbypacketsfromsourcetodest.Routingalgorithms•switching:movepacketsfromrouter’sinputtoappropriaterouteroutput•callsetup:somenetworkarchitecturesrequireroutercallsetupalongpathbeforedataflowsnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysicalNetworkservicemodelQ:Whatservicemodelfor“channel”transportingpacketsfromsendertoreceiver?•guaranteedbandwidth?•preservationofinter-packettiming(nojitter)?•loss-freedelivery?•in-orderdelivery?•congestionfeedbacktosender????virtualcircuitordatagram?Themostimportantabstractionprovidedbynetworklayer:serviceabstractionVirtualcircuits•callsetup,teardownforeachcallbeforedatacanflow•eachpacketcarriesVCidentifier(notdestinationhostID)•everyrouteronsource-destpathmaintains“state”foreachpassingconnection–(incontrast,transport-layerconnectiononlyinvolvedtwoendsystems)•link,routerresources(bandwidth,buffers)maybeallocatedtoVC–togetcircuit-likeperformance“source-to-destpathbehavesmuchliketelephonecircuit”–performance-wise–networkactionsalongsource-to-destpathVirtualcircuits:signalingprotocols•usedtosetup,maintain,andteardownVC•usedinATM,frame-relay,X.25•notusedintoday’sInternetapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysical1.Initiatecall2.incomingcall3.Acceptcall4.Callconnected5.Dataflowbegins6.ReceivedataDatagramnetworks:theInternetmodel•nocallsetupatnetworklayer•routers:nostateaboutend-to-endconnections–nonetwork-levelconceptof“connection”•packetstypicallyroutedusingdestinationhostID–packetsbetweensamesource-destpairmaytakedifferentpathsapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysical1.Senddata2.ReceivedataNetworklayerservicemodels:NetworkArchitectureInternetATMATMATMATMServiceModelbesteffortCBRVBRABRUBRBandwidthnoneconstantrateguaranteedrateguaranteedminimumnoneLossnoyesyesnonoOrdernoyesyesyesyesTimingnoyesyesnonoCongestionfeedbackno(inferredvialoss)nocongestionnocongestionyesnoGuarantees?•Internetmodelbeingextended:Intserv,Diffserv–Chapter6DatagramorVCnetwork:why?Internet•dataexchangeamongcomputers–“elastic”service,nostricttimingreq.•“smart”endsystems(computers)–canadapt,performcontrol,errorrecovery–simpleinsidenetwork,complexityat“edge”•easiertoconnectmanylinktypes–differentcharacteristics–uniformservicedifficultATM•evolvedfromtelephony•humanconversation:–stricttiming,reliabilityrequirements–needforguaranteedservice•“dumb”endsystems–telephones–complexityinsidenetworkRoutingGraphabstractionforroutingalgorithms:•graphnodesarerouters•graphedg...