交换网络的路由技术

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1、Routing2routingManyconnectionswillneedpathsthroughmorethanoneswitchNeedtofindarouteEfficiencyResiliencePublictelephoneswitchesareatreestructureStaticroutingusesthesameapproachallthetimeDynamicroutingallowsforchangesinroutingdependingontrafficUsesapeerstructurefornodes3Rout

2、ingRequirementsCharacteristicsrequiredCorrectnessSimplicityRobustnessStabilityFairnessOptimalityEfficiency4PerformanceCriteriaUsedforselectionofrouteMinimumhopLeastcost5DecisionTimeandPlaceTimePacketorvirtualcircuitbasisPlaceDistributedMadebyeachnodeCentralizedSourceForexa

3、mple6NetworkInformationSourceandUpdateTimingRoutingdecisionsusuallybasedonknowledgeofnetwork(notalways)DistributedroutingNodesuselocalknowledgeMaycollectinfofromadjacentnodesMaycollectinfofromallnodesonapotentialrouteCentralroutingCollectinfofromallnodesUpdatetimingWhenisn

4、etworkinfoheldbynodesupdatedFixed-neverupdatedAdaptive-regularupdates7AlternateRoutingPossibleroutesbetweenendofficespredefinedOriginatingswitchselectsappropriaterouteRouteslistedinpreferenceorderDifferentsetsofroutesmaybeusedatdifferenttimes8AlternateRoutingDiagram9Routin

5、gStrategiesFixedFloodingRandomAdaptive10FixedRoutingSinglepermanentrouteforeachsourcetodestinationpairDetermineroutesusingaleastcostalgorithm(appendix10A)Routefixed,atleastuntilachangeinnetworktopology11FixedRoutingTables12FloodingNonetworkinforequiredPacketsentbynodetoev

6、eryneighborIncomingpacketsretransmittedoneverylinkexceptincominglinkEventuallyanumberofcopieswillarriveatdestinationEachpacketisuniquelynumberedsoduplicatescanbediscardedNodescanrememberpacketsalreadyforwardedtokeepnetworkloadinboundsCanincludeahopcountinpackets13Flooding

7、Example14PropertiesofFloodingAllpossibleroutesaretriedVeryrobustAtleastonepacketwillhavetakenminimumhopcountrouteCanbeusedtosetupvirtualcircuitAllnodesarevisitedUsefultodistributeinformation(e.g.routing)Drawback:hightrafficloadthatitgenerates,whichisdirectlyproportionaltot

8、heconnectivityofthenetwork15RandomRoutingNodeselectsoneoutgoingpathforretransmissionofincom