信息工程网络双语 (14)

WilliamStallingsDataandComputerCommunications7thEditionChapter19InternetworkOperation19.1Multicasting组播AddressesthatrefertogroupofhostsononeormorenetworksUsesMultimedia“broadcast”TeleconferencingDatabaseDistributedcomputingRealtimeworkgroupsExampleConfig组播服务器组成员路由器局域网路由器链路BroadcastandMultipleUnicastBroadcastacopyofpackettoeachnetworkRequires13copiesofpacketMultipleUnicastSendpacketonlytonetworksthathavehostsingroup11packetsTrueMulticastDetermineleastcostpathtoeachnetworkthathashostingroupTransmitsinglepacketalongspanningtreeRoutersreplicatepacketsatbranchpointsofspanningtree8packetsrequiredMulticastExampleInternetGroupManagementProtocol(IGMP)互联网组管理协议P622RFC3376HostandrouterexchangeofmulticastgroupinfoDefinestwoIGMPmessagetypes:MembershipQuery询问：sentbyamulticastrouterMembershipReport报告:sentbyahostIGMPisagroupmanagementprotocol.Ithelpsamulticastroutercreateandupdatealistofloyalmembersrelatedtoeachrouterinterface.19.2RoutingProtocolsp626Inasimpleinternet,afixedroutingschemeispossible.Inmorecomplexinternets,dynamiccooperationisneededamongtherouters.RoutersexchangeroutinginformationusingroutingprotocolAutonomousSystems(AS)自治系统1.Setofroutersandnetworksmanagedbysingleorganization2.Groupofroutersexchangeinformationviaacommonroutingprotocol3.AconnectednetworkAutonomoussystemsInteriorRouterProtocol(IRP)ExteriorRoutingProtocol(ERP)IRP(InteriorRouterProtocol,内部路由器协议)PassesroutinginformationbetweenrouterswithinASe.g.interiorgatewayprotocol,IGPERP(exteriorrouterprotocol,外部路由器协议)RoutersneedsomeinfoaboutnetworksoutsidetheirASe.g.exteriorgatewayprotocol,EGPPopularroutingprotocolsApproachestoRoutingp627threeapproaches:distance-vectorrouting,link-staterouting,andpath-vectorrouting.Distance-vector:距离向量路由选择Eachnode(routerorhost)exchangeinformationwithneighboringnodesinthesamenetworkNodemaintainsvectoroflinkcostsforeachdirectlyattachednetworkanddistanceandnext-hopvectorsforeachdestinationfirstgenerationroutingalgorithmforARPANETUsedforRIP(Routerinformationprotocol)ApproachestoRouting–Link-state:链路状态路由选择Whenrouterinitialized,itdetermineslinkcostoneachinterfaceAdvertisessetoflinkcoststoallotherroutersintopologyEachroutercanconstructtopologyofentireconfigurationRouterconstructsroutingtable,listingfirsthoptoeachdestinationUsedinsecondgenerationroutingalgorithmforARPANETUsedforOSPF(Openshortestpathfirst)protocolApproachestoRouting––Path-vector:路径向量路由选择ProvideinformationaboutwhichnetworkscanbereachedbyagivenrouterandASscrossedtogetthereDoesnotincludedistanceorcostestimateEachblockofinformationlistsallASsvisitedonthisrouteExteriorRouterProtocolsPathvectorpacketsBorderGatewayProtocol(BGP)边界网关协议P629PreferredERPfortheInternetBGPwasdesignedtoallowrouters,calledgatewaysinthestandard,indifferentAsstocooperateintheexchangeofroutinginformation.BGPMessagesMessagessent•Open•Update•Keepalive•Notification不可行撤销BGPMessagesRouterfirstOpensTCPconnectiontotheneighborThensendsOpenmessageIncludesholdtime保持时间一方从另一方收到保活或更新报文前经过的最大秒数。若路由器在此期间内未收到，认为对方不工作。KeepAlivemessage保活报文TotellotherroutersthatthisrouterisstillhereUpdatemessage更新报文InfoaboutsingleroutesthroughinternetListofroutesbeingwithdrawnBGPMessagesNotificationMessage通知报文MessageheadererrorOpenmessageerrorUpdatemessageerrorHoldtimeexpiredFinitestatemachineerrorCeaseBGPusestheservicesofTCPonport179.OpenShortestPathFirstProtocol–OSPF开放最短路径优先协议p634IRPofInternetUsesLinkStateRoutingRoutecomputedonleastcostbasedonusercost(Dijkstraalgorithm)OSPFpacketsareencapsulatedinIPdatagrams.OpenShortestPathFirstTopologystoredasdirectedgraphVertices顶点ornodes节点RouterNetworkTransit转送网络Stub残桩网络EdgesSampleASDirectedGraphofAS•Arcs(弧)arelabeledwiththecost•Arcsleadingfromnetworkstoroutersalwayshaveacostof0SPFTreeforRouter6RoutingTableforR619.3IntegratesServicesArchitectureISA综合服务体系结构p637ISA,intendtoprovideQoS(qualityofservice)transportTrafficonanetworkcanbedividedintotwobroadcategories:Elastic弹性通信量Cancopewithwidechangesindelayand/orthroughputFTPsensitivetothroughput,E-MailinsensitivetodelayNetworkManagementsensitivetodelayWebsensitivetodelayInelastic非弹性通信量Doesnoteasilyadapttovariations.E.g.realtimetrafficFigure19.10ISAimplementedinRouter路由器中综合服务体系结构的实现P642管理代理准许控制预约协议通信量控制数据库路由选择协议路由选择数据库分类程序和路由选择分组调度程序尽最大努力排队QoS排队TokenBucketTrafficSpecification令牌桶通信量规约Tokenreplenishment（补给）rateRContinuallysustainable(可持续的）datarateBucketsizeBAmountthatdataratecanexceedRforshortperiodDuringtimeperiodTamountofdatasentcannotexceedRT+BTokenBucketScheme令牌桶机制令牌生成器令牌补充速率R1.路由器以预定速率投放令牌桶的大小为Bbit到达的分组离开的分组2.令牌可以累积到桶的大小，丢弃超出的令牌3.通行量寻求网络的许可4.路由器的队列调节器要求令牌的数量等于下一个分组的尺寸5.如果令牌足够，分组排队输出6.如果令牌不够，分组或者被标记为超出的，缓存等待稍后传输，或者被丢弃。调节器ResourceReservationProtocol:RSVP资源预约协议P647RFC2205TopreventcongestionbyallowingapplicationstoreservenetworkresourcesatagivenQoSUnicast(单播)Ifroutercannotmeetrequest,applicationinformedMulticast(组播)ismoredemandingMaybereduced