川大软院计网选择题答案Chapter3

CHAPTER3:TRANSPORTLAYER1.Atransport-layerprotocolprovidesforlogicalcommunicationbetween___C_.A.RoutersB.HostsC.ApplicationprocessesD.Endsystems2.Transport-layerprotocolsrunin__D__.A.ServersB.ClientsC.RoutersD.Endsystems3.Intransportlayer,thesendsidebreaksapplicationmessagesinto___B_,passestonetworklayer.A.FramesB.SegmentsC.Data-gramsD.bitstreams4.Thereceivesideoftransportlayerreassemblessegmentsintomessages,passesto__A__layer.A.ApplicationB.NetworkingC.PhysicalD.MAC5.Servicesprovidedbytransportlayerinclude__C__.A.HTTPandFTPB.TCPandIPC.TCPandUDPD.SMTP6.WhichofthefollowingservicesisnotprovidedbyTCPDA.In-orderdatatransfersB.ReliabledatatransfersandflowcontrolsC.CongestioncontrolsD.Delayguaranteesandbandwidthguarantees7.Thesetwominimaltransport-layerservices----___A_and____----aretheonlytwoservicesthatUDPprovidesA.process-to-processdatadelivery,errorcheckingB.congestioncontrol,reliabledatatransfer1C.flowcontrol,congestioncontrolD.In-orderdatatransfer,errorchecking8.UDPofferswhichofthefollowingbenefitsrelativetoTCPCA.UDPguaranteesthatIndividualpacketsofatransmissionwillarrive“inorder”B.UDPsupportsaself-regulating“throttle”featurethatpreventsnetworksaturationC.UDPconsumesfewercomputerresourcesbynotmaintainingconnectionstateD.Noneoftheabove9.WhichofthefollowingapplicationsnormallyusesUDPservicesBA.SMTPB.StreamingmultimediaC.FTPD.HTTP10.Thejobofgatheringdatachunks,encapsulatingeachdatachunkwithheaderinformationtocreatesegmentsandpassingthesegmentstothenetworkiscalled__A__.A.multiplexingB.de-multiplexingC.forwardingD.routing11.Thisjobofdeliveringthedatainatransport-layersegmenttothecorrectsocketiscalled_B___.A.multiplexingB.de-multiplexingC.forwardingD.routing12.Portnumber’sscopeis___B_to____.A.0,1023B.0,65535C.0,127D.0,255Theportnumbersrangingfrom__C__to____arecalledwell-knownportnumberandarerestricted.A.0,127B.0,65535C.0,1023D.0,255214.TheUDPheaderhasonlyfourfields,theyare__A__.A.Sourceportnumber,destinationportnumber,lengthandchecksumB.Sourceportnumber,destinationportnumber,sourceIPanddestinationIPC.sourceIP,destinationIP,sourceMACaddressanddestinationMACaddressD.sourceIP,destinationIP,sequencenumberandACKsequencenumberThefieldofLengthinUDPsegmentspecifiesthelengthof___B_.A.theUDPsegment,notincludingtheheaderB.theUDPsegment,includingtheheaderC.theUDPsegment’sheaderD.theLengthfield16.WhichofthefollowingaboutTCPconnectionisnotcorrectAA.ItisabroadcastconnectionB.Itisapoint-to-pointconnectionC.ItisapipelinedconnectionD.ItisafullduplexconnectionInthefollowingfourdescriptionsaboutMSSandMTU,whichoneisnotcorrectCA.TheMSSistypicallysetbyMTUB.TheMSSisthemaximumsizeoftheTCPsegmentincludingheadersC.TheMSSisthemaximumamountofapplication-layerdatainthesegmentD.TheMTUmeansthelargestlink-layerframe__A__isthebytestreamnumberoffirstbyteinthesegment.A.SequencenumberB.ACKnumberC.ChecksumD.portnumber__B__isthebytesequencenumbersofnextbyteexpectedfromotherside.A.SequencenumberB.ACKnumberC.ChecksumD.portnumber3Inthefollowingfouroptions,whichoneiscorrectDA.SupposethatthelastSampleRTTinaTCPconnectionisequalto1sec.ThenthecurrentvalueofTimeoutIntervalwillnecessarilybe≤1secB.Thetimeoutshouldbelessthantheconnection’sRTTC.SupposethatthelastSampleRTTinaTCPconnectionisequalto1sec.ThenthecurrentvalueofTimeoutIntervalwillnecessarilybe≥1secD.ThevariationsintheSampleRTTaresmoothedoutinthecomputationoftheEstimatedRTTTherearetwo16-bitintegers:1110011001100110,1101010101010101.Theirchecksumis__A__.A.011B.100C.111D.000SupposehostAsendshostBoneTCPsegmentwithsequencenumber418,acknowledgementnumber571,and4bytesofdata.Thenthesequencenumberintheacknowledgementtothissegmentis_____C____A.422B.418C.571D.575BecauseTCPonlyacknowledgesbytesuptothefirstmissingbyteinthestream,TCPissaidtoprovide__D__.A.positiveACKsB.SelectiveacknowledgementsC.3duplicateACKsD.CumulativeacknowledgementsIfwedefineNtobethewindowsize,basetobethesequencenumberoftheoldestunacknowledgedpacket,andnext-seq-numtobethesmallestunusedsequencenumber,thentheinterval[nextseqnum,base+N-1]correspondstopacketthat__A__.A.canbesentimmediatelyB.havealreadybeentransmittedandacknowledgedC.cannotbeusedD.havebeensentbutnotyetacknowledged25.WhichofthefollowingisnotapipeliningA.B.Go-Back-NC.SelectiverepeatD.TCP4Whatisthemaindifferencebetweenstop-and-waitandpipelinedreliabledatatransferprotocolBA.ThepipelinedprotocolusestheNAKpackets,whereasinthestop-and-waitprotocolsendersalwayswaitforACKpackets.B.Withthepipelinedprotocol,thesendercansendseveralpacketsinrow,whereasinthestop-and-waitprotocolthesendercannotsendthepacketsinrow.C.Withthepipelinedprotocol,thereceivermustsendoneACKforseveralpackets(cumulativeACK),whereasinthestop-and-waitprotocolthereceivercannotsendthecumulativeACK.D.Thepipelinedprotocolusestimeouts,whereasthestop-and-waitprotocoldoesnotusethetimeout.Fastretransmitmeansinthecasethat__D__duplicateACK-sarereceived,theTCPsenderresendsegmentbeforetimerexpires.A.6B.5C.4D.328.__B__isaspeeding-matchingservice---matchingtheratewhichthesenderissendingagainsttherateatwhichthereceivingapplicationisreading.A.congestioncontrolB.flowcontrolC.sliding-windowcontrolD.variablecontrolTCPprovidesflowcontrolbyhavingthesendermaintainavariablecalledthe__D__.A.bufferB.CongestionwindowC.SlidingwindowD.Receivewindow30.ProvidedRcvBuffer=20,LastByteRcvd=20,LastByteRead=15,thenRcvWindow=__B__.A.14B.15C.16D.10InthefollowingfourdescriptionsaboutTCPconnectionmanagement,whichoneisnotcorrectD5A.EitherofthetwoprocessesparticipatinginaTCPconnectioncanendtheconnectionB.IftheFINbitissetto1,itmeansthatitwantstoclosetheconnectionC.Inthefirsttwostepofthethree-wayhandshake,theclientandserverrandomlychooseaninitialsequencenumberD.Inthethreesegmentsofthethree-wayhandshake,theSYNbitmustbesetto1HowdoesTCPsenderperceivecongestionDA.ThroughatimeouteventB.Thr