川大林峰计网第一次作业

I.MultipleChoiceInthefollowingoptions,whichdoesnotdefineinprotocol?(D)AtheformatofmessagesexchangedbetweentwoormorecommunicatingentitiesBtheorderofmessagesexchangedbetweentwoormorecommunicatingentitiesCtheactionstakenonthetransmissionofamessageorothereventDthetransmissionsignalsaredigitalsignalsoranalogsignalsInthefollowingoptions,whichisdefinedinprotocol?(A)Atheactionstakenonthetransmissionand/orreceiptofamessageorothereventBtheobjectsexchangedbetweencommunicatingentitiesCthecontentintheexchangedmessagesDthelocationofthehosts1.3Whichofthefollowingnodesbelongstothenetworkcore?(C)A.aWebServerB.aHostwithWin2003ServerC.aRouterwithNATserviceD.aSupernodeonSkypeNetwork1.4IntheInternet,theequivalentconcepttoendsystemsis(A).AhostsBserversCclientsDrouters1.5IntheInternet,endsystemsareconnectedtogetherby(C).AcopperwireBcoaxialcableCcommunicationlinksDfiberoptics1.6EndsystemsaccesstotheInternetthroughits(C).AmodemsBprotocolsCISPDsockets1.7Inthefollowingoptions,whichbelongstothenetworkcore?(B)AendsystemsBroutersCclientsDservers1.8Endsystems,packetswitches,andotherpiecesoftheInternet,run(D)thatcontrolthesendingandreceivingofinformationwithintheInternet.AprogramsBprocessesCapplicationsDprotocols1.9Theprotocolsofvariouslayersarecalled(A).AtheprotocolstackBTCP/IPCISPDnetworkprotocol1.10IntheOSIreferencemodel,theupperlayersoftheOSImodelare,incorrectorder(D)a)Session,application,presentationb)Session,presentation,applicationc)Session,application,presentation,physicald)Application,presentation,session1.11ThelowerlayersoftheOSImodelare,incorrectorder(D)a)physical,system,network,logicalb)physical,logical,network,systemc)physical,transport,network,datalinkd)physical,datalink,network,transport1.12WhichofthefollowingprotocollayersisnotexplicitlypartoftheInternetProtocolStack?___B______A.applicationlayerB.sessionlayerC.datalinklayerD.transportlayer1.13The5-PDUiscalled__D_A.messageB.segmentC.datagramD.frame1.14Transport-layerpacketsarecalled:BA.messageB.segmentC.datagramD.frame1.15Theunitsofdataexchangedbyalink-layerprotocolarecalled(A).AFramesBSegmentsCDatagramsDbitstreams1.16Therearetwofundamentalapproachestobuildinganetworkcore,(B)andpacketswitching.AelectricalcurrentswitchingBcircuitswitchingCdataswitchingDmessageswitching1.17Therearetwoclassesofpacket-switchednetworks:(B)networksandvirtualcircuitnetworks.AdatagramBcircuit-switchedCtelevisionDtelephone1.18(A)meansthattheswitchmustreceivetheentirepacketbeforeitcanbegintotransmitthefirstbitofthepacketontotheoutboundlink.AStore-and-forwardtransmissionBFDMCEnd-to-endconnectionDTDM1.19In(C)networks,theresourcesneededalongapathtoprovideforcommunicationbetweentheendsystemarereservedforthedurationofthecommunicationsession.Apacket-switchedBdata-switchedCcircuit-switchedDmessage-switched1.20In(A)networks,theresourcesarenotreserved;asession’smessagesusetheresourcesondemand,andasaconsequence,mayhavetowaitforaccesstocommunicationlink.Apacket-switchedBdata-switchedCcircuit-switchedDmessage-switched1.21Whichofthefollowingoptionbelongstothecircuit-switchednetworks?(D)AFDMBTDMCVCnetworksDbothAandB1.22Inacircuit-switchednetwork,ifeachlinkhasncircuits,foreachlinkusedbytheend-to-endconnection,theconnectiongets(A)ofthelink’sbandwidthforthedurationoftheconnection.Aafraction1/nBallC1/2Dntimes1.23For(C),thetransmissionrateofacircuitisequaltotheframeratemultipliedbythenumberofbitsinaslot.ACDMABpacket-switchednetworkCTDMDFDM1.24Thenetworkthatforwardspacketsaccordingtohostdestinationaddressesiscalled(D)network.Acircuit-switchedBpacket-switchedCvirtual-circuitDdatagram1.25Thetimerequiredtopropagatefromthebeginningofthelinktothenextrouteris(C).AqueuingdelayBprocessingdelayCpropagationdelayDtransmissiondelay1.26Processingdelaydoesnotincludethetimeto(B).Aexaminethepacket’sheaderBwaittotransmitthepacketontothelinkCdeterminewheretodirectthepacketDcheckbit-errorinthepacket1.27Inthefollowingfourdescriptions,whichoneiscorrect?(C)AThetrafficintensitymustbegreaterthan1.BThefractionoflostpacketsincreasesasthetrafficintensitydecreases.CIfthetrafficintensityisclosetozero,theaveragequeuingdelaywillbeclosetozero.DIfthetrafficintensityisclosetoone,theaveragequeuingdelaywillbeclosetoone.1.28Suppose,aistheaveragerateatwhichpacketsarriveatthequeue,Risthetransmissionrate,andallpacketsconsistofLbits,thenthetrafficintensityis(B),ALR／aBLa／RCRa／LDLR／a1.29anditshouldnogreaterthan(B).A2B1C0D-11.30Supposethereisexactlyonepacketswitchbetweenasendinghostandareceivinghost.ThetransmissionratesbetweenthesendinghostandtheswitchandbetweentheswitchandthereceivinghostareR1andR2,respectively.Assumingthattheswitchusesstore-and-forwardpacketswitching,whatisthetotalend-to-enddelaytosendapacketoflengthL?(Ignorequeuingdelay,propagationdelay,andprocessingdelay.)(A)AL/R1＋L/R2BL/R1CL/R2Dnoneoftheabove1.31Wearesendinga30MbitMP3filefromasourcehosttoadestinationhost.Supposethereisonlyonelinkbetweensourceanddestinationandthelinkhasatransmissionrateof10Mbps.Assumethatthepropagationspeedis2*108meters/sec,andthedistancebetweensourceanddestinationis10,000km.Alsosupposethatmessageswitchingisused,withthemessageconsistingoftheentireMP3file.Howmanybitswillthesourcehavetransmittedwhenthefirstbitarrivesatthedestination?CA.1bitB.30,000,000bitsC.500,000bitsD.noneoftheabove1.32Accessnetworkscanbelooselyclassifiedintothreecategories:residentialaccess,companyaccessand(B)access.AcabledBwirelessCcampusDcityarea1.33Thefollowingtechnologiesmaybeusedforresidentialaccess,exceptDA.HFCB.DSLC.Dial-upmodemD.FDDI1.34Whichkindofmediaisnotaguidedmedia?(D)Atwisted-paircopperwireBacoaxialcableCfiberopticsDdigitalsatellitechannelII.TrueorFalse1.35Thereisnonetworkcongestioninacircuitswitchingnetwork.False1.36Consideranapplicationthattransmitsdataatasteadyrate,andoncethisapplicationstarts,itwillstayonforarelativelylongperiodoftime.Accordingtothecharacteristic,apacket-switchednetworkwouldbemoreappropriateforthisapplicationthanacircuit-switchednetwork.FalseIII.PleaseAnswerFollowingQuestionsBriefly1.37HowmanylayersarethereintheInternetprotocolstack?Whatarethey?Whataretheprincipalresponsibilitiesofeachoftheselayers?5层。分别是application,transport,network,link，physical.Application的协议决定不同主机的不同进程的信息传输，trasport的协议决定不同主机的信息传输，newwork的协议决定信息与目标主机的传输，link的协议决定不同的router之间的信息传输.1.38Iftheunitexchangedatthedatalinkleveliscalledaframeandtheunitexchangedatthenetworkleveliscalledapacket,doframesencapsulatepacketsordopacketsencapsulateframes?Explainyouranswer.是包封装帧。1.39WhentwoapplicationscommunicateovertheInternet,whichoneistheserver?发出请求的是用户，接受请求并返回response的是server。1.40Givefourtypesofdelayalongwithanexplanationofeach.Processingdelay:数据从一个服务器到另一个服务器所需的时间Queueingdelay:很多包在到达交换机之前会排队，排队所需的时间为QueueingdelayTransmissiondelay:包从router到传输介质所需的时间Propagationdelay:包在传输介质中传输所需的时间1.41SupposeHostAwantstosendalargefiletoHostB.ThepathfromHostAtoHostBhasthreelinks,ofratesR1=500kbps,R2=2Mbps,andR3=1Mbps.a.Assumingnoothertrafficinthenetwork,whatisthethroughputforthefiletransfer?b.Supposethefileis4millionbytes.Dividingthefilesizebythethroughput,roughlyhowlongwillittaketotransferthefiletoHostB?c.Repeat(a)and(b),butnowwithR2reducedto100kbps.a.R1<R2<R3,所以吞吐量等于R1=500kbpsb.4MB/500kbps=8sc.a)R2<R1<R3,所以吞吐量等于R2=100Kbpsb)4MB/100kbps=40s1.42(a)SupposeNpacketsarrivesimultaneouslytoalinkatwhichnopacketsarecurrentlybeingtransmittedorqueued.EachpacketisoflengthLandthelinkhastransmissionrateR.WhatistheaveragequeuingdelayfortheNpackets?(b)NowsupposethatNsuchpacketsarrivetothelinkeveryLN/Rseconds.Whatistheaveragequeuingdelayofapacket?a.第一个包的延迟为0，第二个包的延迟为L/R,第三个包的延迟为2L/R,第N个包的延迟为(N-1)/R，因此平均延迟为(0+1+2+….+N-1)/N*L/R=(N-1)/2*L/Rb.经过LN/R秒后N个包已经传送完毕，因此每次传送N个包的延迟都为(N-1)/2*L/R,因此总的平均延迟也为（N-1)/2*L/R1.43Considersendingapacketof3000bitsoverapathof5links.Eachlinktransmitsat1000bps.Queuingdelays,propagationdelayandprocessingdelayarenegligible.(1)Supposethenetworkisapacket-switcheddatagramnetworkandaconnectionlessserviceisused.Nowsupposeeachpackethas200bitsofheader.Howlongdoesittaketosendthefile?(2)Supposethatthenetworkisacircuit-switchednetwork.Furthersupposethatthetransmissionrateofthecircuitbetweensourceanddestinationis200bps.Assuming0.02ssetuptimeand200bitsofheaderappendedtothepacket,howlongdoesittaketosendthepacket?（1）有5条link，因此有5次transmissiondelay,每次的延迟为(3000+200)/1000=3.2s总共花费时间t=5*3.2=16s(2)t=（3000+200）/200+0.02=16.02s1.44Inmodernpacket-switchednetworks,includingtheInternet,thesourcehostsegmentslong,application-layermessages(forexample,animageoramusicfile)intosmallerpacketsandsendsthepacketsintothenetwork.Thereceiverthenreassemblesthepacketsbackintotheoriginalmessage.Werefertothisprocessasmessagesegmentation.TheFigurebelowillustratestheend-to-endtransportofamessagewithandwithoutmessagesegmentation.Consideramessagethatis8·106bitslongthatistobesentfromsourcetodestinationinthefigure.Supposeeachlinkinthefigureis2Mbps.Ignorepropagation,queuing,andprocessingdelays.a)Considersendingthemessagefromsourcetodestinationwithoutmessagesegmentation.Howlong