川大软院计网选择题答案Chapter3(含答案)Word文件下载.docx
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4.Thereceivesideoftransportlayerreassemblessegmentsintomessages,passesto
Alayer.
A.Application
B.Networking
C.Physical
D.MAC
5.ServicesprovidedbytransportlayerincludeC.
A.HTTPandFTP
B.TCPandIP
C.TCPandUDP
D.SMTP
6.WhichofthefollowingservicesisnotprovidedbyTCP?
D
A.In-orderdatatransfers
B.Reliabledatatransfersandflowcontrols
C.Congestioncontrols
D.Delayguaranteesandbandwidthguarantees
7. Thesetwominimaltransport-layerservices---- A_and ----aretheonlytwoservicesthatUDPprovides
A.process-to-processdatadelivery,errorchecking
B.congestioncontrol,reliabledatatransfer
C.flowcontrol,congestioncontrol
D.In-orderdatatransfer,errorchecking
8.UDPofferswhichofthefollowingbenefitsrelativetoTCP?
C
A.UDPguaranteesthatIndividualpacketsofatransmissionwillarrive“inorder”
B. UDPsupportsaself-regulating“throttle”featurethatpreventsnetworksaturation
C. UDPconsumesfewercomputerresourcesbynotmaintainingconnectionstate
D.Noneoftheabove
9.WhichofthefollowingapplicationsnormallyusesUDPservices?
B
A.SMTP
B.Streamingmultimedia
C.FTP
D.HTTP
10.Thejobofgatheringdatachunks,encapsulatingeachdatachunkwithheaderinformationtocreatesegmentsandpassingthesegmentstothenetworkiscalled
A.
A.multiplexing
B.de-multiplexing
C.forwarding
D.routing
11.Thisjobofdeliveringthedatainatransport-layersegmenttothecorrectsocketiscalled_B .
12.Portnumber’sscopeis B_to .A. 0,1023
B. 0,65535
C. 0,127
D. 0,255
13.TheportnumbersrangingfromCto numberandarerestricted.
A. 0,127
C. 0,1023
arecalledwell-knownport
14.TheUDPheaderhasonlyfourfields,theyareA.
A.Sourceportnumber,destinationportnumber,lengthandchecksum
B.Sourceportnumber,destinationportnumber,sourceIPanddestinationIP
C.sourceIP,destinationIP,sourceMACaddressanddestinationMACaddress
D. sourceIP,destinationIP,sequencenumberandACKsequencenumber
15.ThefieldofLengthinUDPsegmentspecifiesthelengthof B_.
A.theUDPsegment,notincludingtheheader
B.theUDPsegment,includingtheheader
C.theUDPsegment’sheader
D.theLengthfield
16.WhichofthefollowingaboutTCPconnectionisnotcorrect?
A
A.Itisabroadcastconnection
B.Itisapoint-to-pointconnection
C.Itisapipelinedconnection
D.Itisafullduplexconnection
17.InthefollowingfourdescriptionsaboutMSSandMTU,whichoneisnotcorrect?
A.TheMSSistypicallysetbyMTU
B.TheMSSisthemaximumsizeoftheTCPsegmentincludingheaders
C.TheMSSisthemaximumamountofapplication-layerdatainthesegment
D.TheMTUmeansthelargestlink-layerframe
18.Aisthebytestreamnumberoffirstbyteinthesegment.
A.Sequencenumber
B.ACKnumber
C.Checksum
D.portnumber
19.Bisthebytesequencenumbersofnextbyteexpectedfromotherside.
20.Inthefollowingfouroptions,whichoneiscorrect?
A.SupposethatthelastSampleRTTinaTCPconnectionisequalto1sec.ThenthecurrentvalueofTimeoutIntervalwillnecessarilybe≤1sec
B.Thetimeoutshouldbelessthantheconnection’sRTT
C. SupposethatthelastSampleRTTinaTCPconnectionisequalto1sec.ThenthecurrentvalueofTimeoutIntervalwillnecessarilybe≥1sec
D.ThevariationsintheSampleRTTaresmoothedoutinthecomputationofthe
EstimatedRTT
21.Therearetwo16-bitintegers:
1110011001100110,1101010101010101.
TheirchecksumisA.A. 0100010001000011
B. 1011101110111100
C. 1111111111111111
D. 1000000000000000
22.SupposehostAsendshostBoneTCPsegmentwithsequencenumber418,acknowledgementnumber571,and4bytesofdata.ThenthesequencenumberintheacknowledgementtothissegmentisC
A.422 B.418 C.571 D.575
23.BecauseTCPonlyacknowledgesbytesuptothefirstmissingbyteinthestream,TCPissaidtoprovideD.
A.positiveACKs
B.Selectiveacknowledgements
C.3duplicateACKs
D.Cumulativeacknowledgements
24.IfwedefineNtobethewindowsize,basetobethesequencenumberoftheoldestunacknowledgedpacket,andnext-seq-numtobethesmallestunusedsequencenumber,thentheinterval[nextseqnum,base+N-1]correspondstopacketthatA.
A.canbesentimmediately
B.havealreadybeentransmittedandacknowledged
C.cannotbeused
D.havebeensentbutnotyetacknowledged
25.Whichofthefollowingisnotapipeliningprotocol.A
A.Rdt1.0
B.Go-Back-N
C.Selectiverepeat
D.TCP
26.Whatisthemaindifferencebetweenstop-and-waitandpipelinedreliabledatatransferprotocol?
A.ThepipelinedprotocolusestheNAKpackets,whereasinthestop-and-waitprotocolsendersalwayswaitforACKpackets.
B.Withthepipelinedprotocol,thesendercansendseveralpacketsinrow,whereasinthestop-and-waitprotocolthesendercannotsendthepacketsinrow.
C.Withthepipelinedprotocol,thereceivermustsendoneACKforseveralpackets（cumulativeACK）,whereasinthestop-and-waitprotocolthereceivercannotsendthecumulativeACK.
D.Thepipelinedprotocolusestimeouts,whereasthestop-and-waitprotocoldoesnotusethetimeout.
27.FastretransmitmeansinthecasethatDduplicateACK-sarereceived,theTCPsenderresendsegmentbeforetimerexpires.
A.6
B.5
C.4
D.3
28.Bisaspeeding-matchingservice---matchingtheratewhichthesenderissendingagainsttherateatwhichthereceivingapplicationisreading.
A.congestioncontrol
B.flowcontrol
C.sliding-windowcontrol
D.variablecontrol
29.TCPprovidesflowcontrolbyhavingthesendermaintainavariablecalledthe
D.
A.buffer
B.Congestionwindow
C.Slidingwindow
D.Receivewindow
30.ProvidedRcvBuffer=20,LastByteRcvd=20,LastByteRead=15,thenRcvWindow=B.
A.14
B.15
C.16
D.10
31.InthefollowingfourdescriptionsaboutTCPconnectionmanagement,whichoneisnotcorrect?
A.EitherofthetwoprocessesparticipatinginaTCPconnectioncanendtheconnection
B.IftheFINbitissetto1,itmeansthatitwantstoclosetheconnection
C. Inthefirsttwostepofthethree-wayhandshake,theclientandserverrandomlychooseaninitialsequencenumber
D.Inthethreesegmentsofthethree-wayhandshake,theSYNbitmustbesetto1
32.HowdoesTCPsenderperceivecongestion?
A.Throughatimeoutevent
B.ThroughareceivingduplicateACK-sevent
C.BothAandB
D.EitherAorB
33.TherearetwostatesinTCPcongestioncontrol,whichare_C .
A.safestartandcongestionabandon
B.safestartandcongestionavoidance
C.slowstartandcongestionavoidance
D.slowstartandcongestionabandon
34.InTCP,thetimeoutintervalisafunctionof:
A.estimatedRTTatthesender B.MSSandtheoverheadofasegment
B.thesizeofbufferatthereceiver D.thesizeofsendingwindow
35.InaTCPconnection,thereistimeouteventwhenthevalueofthresholdis32andthesizeofcongestionwindowis16.AccordingtotheTCPcongestioncontrolpolicy,thenewvalueofthresholdandthenewsizeofcongestionwindowshouldbe C,respectively.
A.16,8 B.24,8 C.8,1 D.16,1
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