计网-第四章作业.docx

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1、Chapter44.1,4.2,4.3节后作业1.(R3)Whatarethetwomostimportantnetwork-layerfunctionsinadatagramnetwork?Whatarethethreemostimportantnetwork-layerfunctionsinavirtual-circuitnetwork?答：forwardingandrouting.forwarding,routingandconnectionsetup.2.(R2)Whatisthedifferen

2、cebetweenroutingandforwarding?答：Forwardingisaboutmovingapacketfromarouter’sinputlinktotheappropriateoutputlink.Routingisaboutdeterminingtheend-to-routesbetweensourcesanddestinations.3.(R9)Describehowpacketlosscanoccuratinputports.Describehowpacketlossatin

3、putportscanbeeliminated(withoutusinginfinitebuffers).答：Thequeuesizeattheinputportgrowslargebecauseofslowswitchingfabricspeedandexhaustingrouter’sbufferspace.Itcanbeeliminatediftheswitchingfabricspeedisatleastntimesasfastastheinputlinespeed,wherenisthenumb

4、erofinputports.4.4,4.5,4.6,4.7节后作业4.(R12)Whatisthe32-bitbinaryequivalentoftheIPaddress223.1.3.27?答：5.DoroutershaveIPaddresses?Ifso,howmany?答：Yes.Theyhaveoneaddressforeachinterface.6.ConsiderFigure4.34.StartingwiththeoriginaltableinD,supposethatDreceivesfr

5、omAthefollowingadvertisement.WillthetableinDchange?Ifsohow?答：No.IftheadvertisementsaidthatAwereonly4hopsawayfromzbywayofC,thenDwouldindeedchangeitsforwardingtable.1.(P8)Consideradatagramnetworkusing32-bithostaddresses.Supposearouterhasfivelinks,numbered0t

6、hrough4,andpacketsaretobeforwardedtothelinkinterfacesasfollows:DestinationAddressRangeLinkInterfaceThrough0Through1Through2Through3Otherwise4a.Provideaforwardingtablethathasfiveentries,useslongestprefixmatching,andforwardspacketstothecorrectlinkinterfaces

7、.b.Describehowyourforwardingtabledeterminestheappropriatelinkinterfacefordatagramswithdestinationaddresses:答：a.IPLinkinterface0123Otherwise4b.Prefixmatchforfirstaddressis4thentry:linkinterface3Prefixmatchforsecondaddressis2ndentry:linkinterface1Prefixmatc

8、hforfirstaddressis3rdentry:linkinterface21.(P9)Consideradatagramnetworkusing4bithostaddresses.Supposearouteruseslongestprefixmatchingandhasthefollowingforwardingtable:PrefixMatchInterface000011102113Foreachofthefour