文档介绍：路由协议intra-domain:RIP,OSPFinter-domain:路由协议intra-domain:RIP,OSPFinter-domain:ServiceProviders(ISPs)AllotherIPservicesdependonconnectivity:DNS,email,VPNs,WebHosting,…,routerthreeimportantfunctions:pathdetermination::movepacketsfromrouter’sinputtoappropriaterouteroutputcallsetup:NxtHopABCDEdefaultR1DirectR3R1R3R1DefaulttoupstreamrouterABCDEdefaultForwarding:determinenexthopRouting:findend-to-workservicemodelQ:Whatservicemodelfor“channel”transportingpacketsfromsendertoreceiver?guaranteedbandwidth?preservationofinter-packettiming(nojitter)?loss-freedelivery?in-orderdelivery?congestionfeedbacktosender????virtualcircuitordatagram?worklayer:serviceabstraction清华大学研究生课程8VirtualcircuitscallsetupforeachcallbeforedatacanfloweachpacketcarriesVCidentifier(notdestinationhostID)everyrouteronsource-destpathmaintains“state”foreachpassingconnectionlink,routerresources(bandwidth,buffers)maybeallocatedtoVC“source-to-destpathbehavesmuchliketelephonecircuit”performance-workactionsalongsource-to-destpath清华大学研究生课程9Virtualcircuits: signalingprotocolsusedtosetup,maintain,teardownVCusedinATM,frame-relay,’: worklayerrouters:nostateaboutend-to-