网络层协议设计徐恪清华大学计算机系清华大学研究生课程清华大学研究生课程*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*VirtualcircuitscallsetupforeachcallbeforedatacanfloweachpacketcarriesVCidentifier(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*Virtualcircuits: signalingprotocolsusedtosetup,maintain,teardownVCusedinATM,frame-relay,’*works: worklayerrouters:nostateaboutend-to-
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