计算机网络英文课件

NetworkLayer4-1Chapter4:NetworkLayerChaptergoals:understandprinciplesbehindnetworklayerservices:networklayerservicemodelsforwardingversusroutinghowarouterworksrouting(pathselection)dealingwithscaleadvancedtopics:IPv6,mobilityinstantiation,implementationintheInternetNetworkLayer4-2Chapter4:NetworkLayer4.1Introduction4.2Virtualcircuitanddatagramnetworks4.3What’sinsidearouter4.4IP:InternetProtocolDatagramformatIPv4addressingICMPIPv64.5RoutingalgorithmsLinkstateDistanceVectorHierarchicalrouting4.6RoutingintheInternetRIPOSPFBGP4.7BroadcastandmulticastroutingNetworkLayer4-3Networklayertransportsegmentfromsendingtoreceivinghostonsendingsideencapsulatessegmentsintodatagramsonrcvingside,deliverssegmentstotransportlayernetworklayerprotocolsineveryhost,routerRouterexaminesheaderfieldsinallIPdatagramspassingthroughitnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysicalNetworkLayer4-4TwoKeyNetwork-LayerFunctionsforwarding:movepacketsfromrouter’sinputtoappropriaterouteroutputrouting:determineroutetakenbypacketsfromsourcetodest.routingalgorithmsanalogy:routing:processofplanningtripfromsourcetodestforwarding:processofgettingthroughsingleinterchangeNetworkLayer4-51230111valueinarrivingpacket’sheaderroutingalgorithmlocalforwardingtableheadervalueoutputlink01000101011110013221InterplaybetweenroutingandforwardingNetworkLayer4-6NetworkservicemodelExampleservicesforindividualdatagrams:guaranteeddeliveryguaranteeddeliverywithlessthan40msecdelay3b1d3a1c2aAS3AS1AS21a2c2b1b3ceBGPsessioniBGPsessionNetworkLayer4-7Networklayerservicemodels:NetworkArchitectureInternetATMATMATMATMServiceModelbesteffortCBRVBRABRUBRBandwidthnoneconstantrateguaranteedrateguaranteedminimumnoneLossnoyesyesnonoOrdernoyesyesyesyesTimingnoyesyesnonoCongestionfeedbackno(inferredvialoss)nocongestionnocongestionyesnoGuarantees?NetworkLayer4-8Chapter4:NetworkLayer4.1Introduction4.2Virtualcircuitanddatagramnetworks4.3What’sinsidearouter4.4IP:InternetProtocolDatagramformatIPv4addressingICMPIPv64.5RoutingalgorithmsLinkstateDistanceVectorHierarchicalrouting4.6RoutingintheInternetRIPOSPFBGP4.7BroadcastandmulticastroutingNetworkLayer4-9Networklayerconnectionandconnection-lessservicedatagramnetworkprovidesnetwork-layerconnectionlessserviceVCnetworkprovidesnetwork-layerconnectionserviceanalogoustothetransport-layerservices,but:service:host-to-hostnochoice:networkprovidesoneortheotherimplementation:innetworkcoreNetworkLayer4-10Virtualcircuitscallsetup,teardownforeachcallbeforedatacanfloweachpacketcarriesVCidentifier(notdestinationhostaddress)everyrouteronsource-destpathmaintains“state”foreachpassingconnectionlink,routerresources(bandwidth,buffers)maybeallocatedtoVC(dedicatedresources=predictableservice)“source-to-destpathbehavesmuchliketelephonecircuit”performance-wisenetworkactionsalongsource-to-destpathNetworkLayer4-11VCimplementationaVCconsistsof:1.pathfromsourcetodestination2.VCnumbers,onenumberforeachlinkalongpath3.entriesinforwardingtablesinroutersalongpathpacketbelongingtoVCcarriesVCnumber(ratherthandestaddress)VCnumbercanbechangedoneachlink.NewVCnumbercomesfromforwardingtableNetworkLayer4-12Forwardingtable122232123VCnumberinterfacenumberIncominginterfaceIncomingVC#OutgoinginterfaceOutgoingVC#11232226311837217197387…………Forwardingtableinnorthwestrouter:Routersmaintainconnectionstateinformation!NetworkLayer4-13Virtualcircuits:signalingprotocolsusedtosetup,maintainteardownVCusedinATM,frame-relay,X.25notusedintoday’sInternetapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysical1.Initiatecall2.incomingcall3.Acceptcall4.Callconnected5.Dataflowbegins6.ReceivedataNetworkLayer4-14Datagramnetworksnocallsetupatnetworklayerrouters:nostateaboutend-to-endconnectionsnonetwork-levelconceptof“connection”packetsforwardedusingdestinationhostaddresspacketsbetweensamesource-destpairmaytakedifferentpathsapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysical1.Senddata2.ReceivedataNetworkLayer4-15ForwardingtableDestinationAddressRangeLinkInterface11001000000101110001000000000000through01100100000010111000101111111111111001000000101110001100000000000through11100100000010111000110001111111111001000000101110001100100000000through211001000000101110001111111111111otherwise34billionpossibleentriesNetworkLayer4-16LongestprefixmatchingPrefixMatchLinkInterface110010000001011100010011001000000101110001100011100100000010111000112otherwise3DA:11001000000101110001100010101010ExamplesDA:11001000000101110001011010100001Whichinterface?Whichinterface?NetworkLayer4-17DatagramorVCnetwork:why?Internet(datagram)dataexchangeamongcomputers“elastic”service,nostricttimingreq.“smart”endsystems(computers)canadapt,performcontrol,errorrecoverysimpleinsidenetwork,c