計算機網絡試卷

姓名學號學院姓名學號學院專業(yè)座位號(密封線內不答題)……………………密………………封………線……線………_____________________…華南理工大學期末考試《ComputerNetworks》A試卷注意事項：1.考前請將密封線內填寫清楚；2.所有答案請直接答在試卷上(注：選擇題答案請?zhí)钊腩}目前面的表格中)；3．考試形式：閉卷；4.本試卷共五大題，滿分100分,考試時間120分鐘。題號12345總分得分評卷人Selectthecorrectchoice.(30scores,everyoneis2scores)NO.123456789101112131415solutionItisthearchitectureforTCP/IPprotocolstack,whichonebelowdoesn’tbelongtotheapplicationlayer(B)?A.TELNETB.ICMPC.POPD.SMTPWhydoHTTP,FTP,SMTPandPOP3runontopofTCPratherthanUDP?(A)A.ReliabledatatransferB.ThroughputC.Real-timeD.SecuritySupposeHostAwantstosendafiletoHostB,therearethreelinksbetweenAtoB,andtheratesofthethreelinksarerespectivelyR1=2Mbps,R2=1Mbps,andR3=4Mbps.Ifnoanyothertrafficinthenetwork,whatisthethroughputforthefiletransfer?(B)A.2MbpsB.1MbpsC.4MbpsD.7MbpsSupposeanapplicationgenerateschunksof120bytesofdataeverysecond,andeachchunkgetsencapsulatedinaTCPsegmentandthenanIPdatagram(nooptionsfields).Whatpercentageofeachdatagramwillcontainapplicationdata?(B) A.80%B.75%C.60%D.25%Thejobofdeliveringthedatainatransport-layersegmenttothecorrectsocketiscalled(A).A.DemultiplexingB.MultiplexingC.TDMD.FDMConsidersendinga999bytedatagramintoalinkthathasanMTUof500bytes,(B)2fragmentsarecreatedwithoffsetfieldvalue0,500,respectively3fragmentsarecreatedwithoffsetfieldvalue0,480,960,respectively3fragmentsarecreatedwithoffsetfieldvalue0,60,120,respectivelyNoneoftheseaboveAbouttheencapsulationrelationshipsofsegment、datagramandframe,whichofthefollowingiscorrect?(C)A.Segmentisencapsulatedwithintheframe,andtheframeisencapsulatedwithinthedatagram.B.DatagramisencapsulatedwithintheSegment,andtheSegmentisencapsulatedwithintheframe.C.Segmentisencapsulatedwithinthedatagram,andthedatagramisencapsulatedwithintheframe.D.Frameisencapsulatedwithinthedatagram,andthedatagramisencapsulatedwithinthesegment.TCPhaswhichofthefollowingcharacteristics:(D)A.FlowcontrolB.ConnectionestablishmentC.CongestioncontrolD.AlloftheaboveWhatistheICMPusedfor？(C)A.ErrorreportingB.UsedbypingC.AandBD.Noneabove.Ataking-turnsMACprotocolhaswhichofthefollowingcharacteristics:(B)A.thereisnosinglepointfailureB.itdoesnotgeneratecollisionsC.thereisnomasternodeD.alloftheaboveIntheEthernettwo-layerswitches,howistheforwardingtableestablished?(B)A.Manualconfiguration B.Self-learningC.Routingalgorithm D.DestinationaddresslearningWhicharetheerrordetectionandcorrectiontechniquesusedofteninlinklayer?(A)A.CRCB.ChecksumC.ParitychecksD.NoneoftheaboveInroutingamongASs,whichofthefollowingissuesdominants?(A)A.RoutingPolicyB.GeographicaldistancebetweenAssC.CurrentcongestionlevelsintheASsD.NumberofASstraversedAnARPquerypacketisencapsulatedin(B)A.alink-layerframeaddressedtoaspecificadapterB.alink-layerbroadcastframeC.anIPdatagramD.noneoftheaboveTwoimportantreasonsthattheInternetisorganizedasahierarchyofnetworksforthepurposesofroutingare(C)A.LeastcostandmaximumfreecircuitavailabilityB.MessagecomplexityandspeedofconvergenceC.ScaleandadministrativeautonomyD.LinkcostchangesandlinkfailureFilltheblank.(10scores,everyblankis1score)Thetaskofthedatalinklayerisprovidingdatatransmissionservicesbetween_________Adjacentnodes__________;Thetaskofthenetworklayerisprovidingdatatransmissionservicesbetween_______hosts___________;andthetaskoftransportlayerisprovidingdatatransmissionservicesbetween________processes___________.Thetwokeyfunctionsofnetworklayerare_______Forwarding________and________routing__________.TworoutingprotocolshavebeenusedextensivelyforroutingwithinanautonomoussystemintheInternet:RIPprotocoland__OSPF____protocol.TheheaderofIPdatagramhasa_____TTL______field,whenthevalueofthefieldis0,thedatagramtransmittedwillbediscarded.RIPadvertisementstypicallyannouncethenumberofhopstovariousdestination;BGPupdates,ontheotherhand,announcethe________SequenceofASsontheroutes___________tothevariousdestinations.TCPprovidesa________Flowcontrol________servicetoitsapplicationtoeliminatethepossibilityofthesenderoverwhelmingthereceiver.Thetool(command)thatcanbeusedtodeterminethenumberofhopstoadestinationandtheroundtriptime(RTT)foreachhopis______Traceroute________.Judgethefollowingquestionsastrueorfalse.(10scores,everyoneis1scores)

NO.12345678910Solution(TorF)FTFFFTFTFFWhenauserrequestaWebpagethatconsistsofsometextandtwoimages.Forthispage,theclientwillsendonerequestmessageandreceivethreeresponsemessage.Withawindowsizeof1,SR,GBN,andthealternatingbitprotocolarefunctionallyequivalent.Whenusingdistancevectorroutealgorithm,thecompletenetworktopologyinformationmustbeknownbyarouter.InaP2Pfile-sharingapplication,thereisnonotionofclientandserversidesofacommunicationsession.AllnodesconnectedtotheInternetmustimplementUDP.MediaAccessControlisafunctionofthedata-linklayer.Emailsaredeliveredtoreceiver'sserverusingPOP3protocol.BothCIDRandNATcanleadtomuchmoreefficientuseoftheavailableIPv4addressspace.CollisionswillnotoccurunderCSMA/CDMACprotocol.WhenaTCPsegmentarrivestoahost,thesockettowhichthesegmentisdirecteddependsonthedestinationportnumberandthedestinationIPaddress.Answerthefollowingquestionsbriefly.(30scores,everyoneis6scores)Considersendingapacketfromasourcehosttoadestinationhostoverafixedroute.Namethefourfactorsofdelayforthepacket.Isthedelayconstant?Whyorwhynot?Identifywhichfactorwillmostlikelypredominate(i.e.,bethelargestfactor)for1MBytePacketsinaflowonthefollowingdifferentlinks.a)10Mb/sLANsegmentbetweentwoPCsinthesamebuildingb)1Mb/sgeosynchronous-orbitsatellite(同步軌道衛(wèi)星)linkbetweentheUSandChinac)ontheInternetbetweentheUSandChina(2)DomainNameSystem(DNS)usesadistributedapproachasopposedtoasingleserver.Why?AssumeaclientneedstofindtheIPaddressofusingtheDNS.AndassumetheclienthasalocalDNSserver,butthatserverdoesnothaveanyaddressescached.WhataretheDNSserversthatarequeried(inorder)tofindtheIPaddress?TrytodescribethemainprinciplesofreliabledatatransferforGBNasfigure1.Figure1GBNwindowmechanism(4)Considerasubnetwithprefix4/26.GiveanexampleofoneIPaddress(offormxxx.xxx.xxx.xxx)thatcanbeassignedtoaninterfaceinthisnetwork.SupposeanISPownstheblockofaddressesoftheform4/26.Andsupposeitwantstocreatefoursubnetsfromthisblock,witheachblockhavingthesamenumberofIPaddresses.Whataretheprefixes(offorma.b.c.d/x)forthefoursubnets?(5)Asfigure2,supposeHostAsendsadatagramtoHostBviarouterR.PleasedrawupthesourceanddestinationMACaddresses,andsourceanddestinationIPaddressesintheframeasrequiredbelow:FromAtotheRFromRtoB.RR1A-23-F9-CD-06-9BE6-E9-00-17-BB-4BCC-49-DE-D0-AB-7DA74-29-9C-E8-FF-55B49-BD-D2-C7-56-2A88-B2-2F-54-1A-0FFigure2ComprehensiveQuestions(20scores,everyoneis10scores)(1)Considerthefollowingnetwork.Withtheindicatedlinkcosts,useDijkstra’sshortestpathalgorithmtocomputetheshortestpathfromxtoallnetworknodes.Whileselectingthenextnode,ifseveralnodeshavethesamemincost,selecttheonewithlowestid,(e.g.,iftandvhavethesamemincost,thenselectt).Figure4Figure3Pleaseshowhowthealgorithmworksbyfillingoutthefollowingtable.(2)AssumethefollowinggraphshowsthebehaviorofaTCPcongestioncontrol,answereachquestionwithashortdiscussionjustifyingyouranswer.a)IdentifytheintervalsoftimewhenTCPslowstartisoperating.b)IdentifytheintervalsoftimewhenTCPcongestionavoidanceisoperating.c)After14thtransmissionround,issegmentlossdetectedbyatripleduplicateACKorbyatimeout?AndwhichversionofTCPprotocol(RenoorTahoe)isusedbaseonthisinformation?d)Duringwhattransmissionroundisthe50thsegmentsent?e)Assumingapacketlossisdetectedafterthe23rdroundbythereceiptofatripleduplicateACKs,whatwillbethevaluesofthecongestionwindowsizeandThreshold?姓名學號學院姓名學號學院專業(yè)座位號(密封線內不答題)……………………密………………封………線……線………_____________________…華南理工大學期末考試《ComputerNetworks》A試卷Selectthecorrectchoice.(30scores,everyoneis2scores)NO.123456789101112131415solutionBABBABCDCBBAABCFilltheblank.(10scores,everyblankis1score)Adjacentnodes;hosts;processesForwarding,routingOSPFTTLSequenceofASsontheroutesFlowcontrolTraceroute(Tracert)Judgethefollowingquestionsastrueorfalse.(10scores,everyoneis1scores)

NO.12345678910Solution(TorF)FTFFFTFTFFAnswerthefollowingquestionsbriefly.(30scores,everyoneis6scores)(1)nodalprocessingdelay,queuingdelay,transmissiondelay.Propagationdelay.It’notconstant,an