计算机网络英文试题库(附答案)chapter3解析VIP

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实用文档

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Chapter3TransportLayer.

1.Atransport-layerprotocolprovidesforlogicalcommunicationbetween____..

AApplicationprocesses.

BHosts.

CRouters.

DEndsystems.

2.Transport-layerprotocolsrunin____..

AServers.

BClients.

CRouters.

DEndsystems.

3.Intransportlayer,thesendsidebreaksapplicationmessagesinto____,passestonetworklayer..

AFrames.

BSegments.

CData-grams.

Dbitstreams.

4.Servicesprovidedbytransportlayerinclude____..

AHTTPandFTP.

BTCPandIP.

CTCPandUDP.

DSMTP.

5.WhichofthefollowingservicesisnotprovidedbyTCP?.

ADelayguaranteesandbandwidthguarantees.

BReliabledatatransfersandflowcontrols.

CCongestioncontrols.

DIn-orderdatatransfers.

6.Thesetwominimaltransport-layerservices____and____aretheonlytwoservicesthatUDPprovides!.

Aprocess-to-processdatadelivery,errorchecking.

Bcongestioncontrol,reliabledatatransfer.

Cflowcontrol,congestioncontrol.

DIn-orderdatatransfer,errorchecking.

7.Portnumber’sscopeis____to____..

A0,1023.

B0,65535.

C0,127.

D0,255.

8.Theportnumbersrangingfrom____to____arecalledwell-knownportnumberandarerestricted..

A0,1023.

B0,65535.

C0,127.

D0,255.

9.UDPsocketidentifiedbytwocomponents,theyare____..

AsourceIPaddressesandsourceportnumbers.

BsourceIPaddressesanddestinationIPaddresses.

CdestinationIPaddressanddestinationportnumbers.

Ddestinationportnumbersandsourceportnumbers.

10.TCPsocketidentifiedbya(an)____..

A1-tuple.

B2-tuple.

C3-tuple.

D4-tuple.

11.WhichofthefollowingapplicationsnormallyusesUDPservices?.

ASMTP.

BStreamingmultimedia.

CFTP.

DHTTP.

12.

Reliable

data

transfer

protocol

over

a

perfectly

reliable

channel

is____.

.

A

rdt1.0

B

rdt2.0

C

rdt3.0

D

rdt2.1

.

13.

Reliable

data

transfer

protocol

over

a

channel

with

bit

errors

and

packet

losses

is

____.

.

A

rdt1.0

B

rdt2.0

C

rdt3.0

D

rdt2.1

.

14.

Which

of

the

following

about

reliable

data

transfer

over

a

channel

with

bit

errors

is

not

correct?

.

A

RDT2.0:

assuming

ACK

and

NAK

will

not

be

corrupted

.

B

RDT2.1:

assuming

ACK

and

NAK

can

be

corrupted

.

C

RDT2.2:

only

use

ACK-s

.

D

RDT2.2:

use

both

ACK-s

and

NAK-s

.

15.

Which

of

the

following

protocols

is

not

pipelining

protocols?

.

A

TCP

B

rdt3.0

.

C

GO-BACK-N

D

selective

repeat

.

16.

Which

of

the

following

is

not

correct

about

GBN

protocol?

.

A

Only

using

ACK-s

.

B

Using

cumulative

ACK-s

.

C

Receiver

discards

all

out-of-order

packets

.

D

It

is

not

pipelined

protocol

.

17.

Which

of

the

following

is

not

correct

about

SR

protocol?

.

A

receiver

individually

acknowledges

all

correctly

received

packets

.

B

sender

only

resends

packets

for

which

ACK

not

received

.

C

It

limits

sequence

number

of

sent

but

un-ACK-ed

packets

.

D

It

is

not

a

pipelined

protocol.

18.WhichofthefollowingaboutTCPconnectionisnotcorrect?.

AItisabroadcastconnection.

BItisapoint-to-pointconnection.

CItisapipelinedconnection.

DItisafullduplexconnection.

19.TheSYNsegmentisusedfor____..

ATCPconnectionsetup.

BTCPflowcontrol.

CTCPcongestioncontrol.

DClosingaTCPconnection.

20.TheFINsegmentisusedfor____..

ATCPconnectionsetup.

BTCPflowcontrol.

CTCPcongestioncontrol.

DClosingaTCPconnection.

HowdoesTCPsenderperceivecongestion?.

AThroughatimeoutevent.

BThroughareceivingduplicateACK-sevent.

CBothAandB.

DEitherAorB.

22.Extendinghost-to-hostdeliverytoprocess-to-processdeliveryiscalledtransport-layer____and..

Amultiplexingandde-multiplexing.

Bstoringandforwarding.

Cforwardingandfiltering.

Dswitchingandrouting.

23.UDPisa____servicewhileTCPisaconnection-orientedservice..

AConnectionless.

BReliable.

CConnection-oriented.

DIn-order.

24.TheUDPheaderhasonlyfourfields,theyare____..

ASourceportnumber,destinationportnumber,lengthandchecksum.

BSourceportnumber,destinationportnumber,sourceIPanddestinationIP.

CsourceIP,destinationIP,sourceMACaddressanddestinationMACaddress.

DsourceIP,destinationIP,sequencenumberandACKsequencenumber.

25.Therearetwo16-bitintegers:1110011001100110,1101010101010101.Theirchecksumis____..

A0100010001000011.

B1011101110111100.

C1111111111111111.

D1000000000000000.

Themaximumamountofdatathatcanbegrabbedandplacedinasegmentislimitedbythe____..

AMaximumsegmentsize(MSS).

BMTU.

CChecksum.

DSequencenumber.

TheMSSistypicallysetbyfirstdeterminingthelengthofthelargestlink-layerframethatcanbesentbythelocalsendinghosttheso-called____..

AMaximumtransmissionunit(MTU).

BMSS.

CChecksum.

DSequencenumber.

28.AFilesizeof500,000bytes,MSSequals1000bytes.WhenwewanttotransmitthisfilewithTCP,thesequencenumberofthefirstsegmentis0,andthesequencenumberofthesecondsegmentis____..

A1000.

B999.

C1001.

D500000.

BecauseTCPonlyacknowledgesbytesuptothefirstmissingbyteinthestream,TCPissaidtoprovide____..

ACumulativeacknowledgements.

BSelectiveacknowledgements.

C3duplicateACKs.

DpositiveACKs.

30.Providedα=0.125,currentvalueofEstimated-RTTis0.4s,Sample-RTTis0.8s,thenthenewvalueofEstimated-RTTis____s..

A0.45.

B0.6.

C0.7.

D0.8.

ProvidedRcvBuffer=20,LastByteRcvd=20,LastByteRead=15,thenRcvWindow=____..

A14.

B15.

C16.

D10.

32.TCPservicedoesnotprovide____..

AReliabledatatransferBFlowcontrol.

CDelayguaranteeDCongestioncontrol.

33.TherearetwostatesinTCPcongestioncontrol,whichare____..

Aslowstartandcongestionavoidance.

Bsafestartandcongestionavoidance.

Cslowstartandcongestionabandon.

Dsafestartandcongestionabandon.

34.Thetransport-layerprotocolprovideslogicalcommunicationbetween____,andthenetwork-layerprotocolprovideslogicalcommunication____..

Ahosts,processes.

Bprocesses,hosts.

Cthreads,processes.

Dprocesses,threads.

35.

To

implement

the

multicast

services

the

Internet

employs

the

____

protocol.

.

A

FTP

B

TCP

C

IGMP

D

UDP

.

36.Ifanapplicationdeveloperchooses____protocol,thentheapplicationprocessisalmostdirectlytalkingwithIP..

AHTTP.

BRIP.

CCSMA/CD.

DUDP.

37.____maintainsconnection-stateintheendsystems.Thisconnectionstateincludesreceiveandsendbuffers,congestion-controlparameters,andsequenceandacknowledgmentnumberparameters..

AUDP BTCP CDNS DHTTP.

38.ThehostthatinitiatesthesessionintheInternetislabeledas____..

Aserver Buseragent Cclient Drouter.

39.WithTCPthereisno_____betweensendingandreceivingtransport-layerentities..

Aflowcontrol Bhandshaking.

C.congestioncontrol DVCsetup.

40.TheInternet’s____servicehelpspreventtheInternetfromenteringastateofgridlock..

Adatagram Bcongestioncontrol.

Cslidingwindow Dtimeoutevent.

41.Connectionsetupatthetransportlayerinvolves____..

Aserver Bonlythetwoendsystems.

Cclient Drouter.

42.A____layerprotocolprovidesforlogicalcommunicationbetweenapplications..

Atransport.

Bapplication.

Cnetworking.

DMAC.

43.Instaticcongestionwindow,ifitsatisfiesW*S/R>RTT+S/R,theLatencyis____..

AW*S/R–(RTT+S/R).

B2RTT+O/R.

C2RTT+O/R+(k-1)[W*S/R-(RTT+S/R)].

D2RTT+S/R.

44.Thereceivesideoftransportlayerreassemblessegmentsintomessages,passesto____layer..

AApplication.

BNetworking.

CPhysical.

DMAC.

45.Inthefollowingfouroptions,whichoneiscorrect?.

AThevariationsintheSampleRTTaresmoothedoutinthecomputationoftheEstimatedRTT.

BThetimeoutshouldbelessthantheconnection’sRTT.

CSupposethatthelastSampleRTTinaTCPconnectionisequalto1sec.ThenthecurrentvalueofTimeoutIntervalwillnecessarilybe≥1sec.

DSupposethatthelastSampleRTTinaTCPconnectionisequalto1sec.ThenthecurrentvalueofTimeoutIntervalwillnecessarilybe≤1sec.

46.TheportnumberusedbyHTTPis____..

A80.

B25.

C110.

D53.

47.TheportnumberusedbySMTPis____..

A80.

B25.

C110.

D53.

48.Theportnumberusedbypop3is____..

A80.

B25.

C110.

D53.

49.TheportnumberusedbyDNSis____..

A80.

B25.

C110.

D53.

50.TheportnumberusedbyFTPis____..

A20and21.

B20.

C21.

D53.

51.AUDPsocketidentifiedbya____tuple(s)..

A2.

B4.

C1.

D3.

52.ATCPsocketidentifiedbya____tuple(s)..

A2.

B4.

C1.

D3.

53.ATCPsocketdoesnotinclude____..

ASourceMACaddress.

BSourceportnumber.

CDestinationIPaddress.

DDestinationportnumber.

54.WhichoffollowingaboutUDPisnotcorrect..

AItisareliabledatatransferprotocol.

BItisconnectionless.

CnohandshakingbetweenUDPsender,receiver.

Ditisabesteffortserviceprotocol.

55.DNSuses____service..

ATCP.

BUDP.

CBothTCPandUDP.

DNoneofabove.

56.WhichoffollowingaboutUDPiscorrect?.

AFinerapplication-levelcontroloverwhatdataissent,andwhen.

BNoconnectionestablishment(whichcanadddelay),sonodelayforestablishaconnection.

CNoconnectionstate(so,UDPcantypicallysupportmanyactiveclients).

DLargepacketheaderoverhead(16-B).

57.Streamingmediausesa____servicenormally..

ATCP.

BUDP.

CBothTCPandUDP.

DNoneofabove.

58.TheUDPheaderhasonly____fields..

A2.

B4.

C1.

D3.

59.WhichofthefollowingdoesnotincludedinUDPheader..

ASourceportnumber.

BDestinationportnumber.

CChecksum.

DSequencenumber.

60.Whichofthefollowingisnotapipeliningprotocol..

ARdt1.0.

BGo-Back-N.

CSelectiverepeat.

DTCP.

61.InthefollowingfourdescriptionsaboutMSSandMTU,whichoneisnotcorrect?.

ATheMSSisthemaximumamountofapplication-layerdatainthesegment.

BTheMSSisthemaximumsizeoftheTCPsegmentincludingheaders.

CTheMSSistypicallysetbyMTU.

DTheMTUmeansthelargestlink-layerframe.

62.Thejobofgatheringdatachunks,encapsulatingeachdatachunkwithheaderinformationtocreatesegmentsandpassingthesegmentstothenetworkiscalled____..

Amultiplexing.

Bde-multiplexing.

Cforwarding.

Drouting.

63.Inthefollowingfourdescriptionsabouttherelationshipbetweenthetransportlayerandthenetworklayer,whichoneisnotcorrect?.

AThetransport-layerprotocolprovideslogicalcommunicationbetweenhosts.

BThetransport-layerprotocolprovideslogicalcommunicationbetweenprocesses.

CTheservicesthatatransport-layerprotocolcanprovideareoftenconstrainedbytheservicemodelofthenetwork-layerprotocol.

DAcomputernetworkmaymakeavailablemultipletransportprotocols.

64.Supposethefollowingthree8-bitbytes:01010101,01110000,01001100.What’sthe1scomplementofthesumofthese8-bitbytes?.

A00010001.

B11101101.

C00010010.

D10001000.

65.Thefollowingfourdescriptionsaboutmultiplexingandde-multiplexing,whichoneiscorrect?.

AAUDPsocketisidentifiedbyatwo-tuplesconsistingofasourceportnumberandadestinationportnumber..

BIftwoUDPsegmenthavedifferentsourceportnumber,theymaybedirectedtothesamedestinationprocess..

CIftwoTCPsegmentswithdifferentsourceportnumber,theymaybedirectedtothesamedestinationprocess..

DIftwoTCPsegmentswithsamedestinationIPaddressanddestinationportnumber,theymustbethesameTCPconnection..

66.UDPandTCPbothhavethefieldsexcept____..

Asourceportnumber.

Bdestinationportnumber.

Cchecksum.

Dreceivewindow.

67.IfwedefineNtobethewindowsize,basetobethesequencenumberoftheoldestunacknowledgedpacket,andnext-seq-numtobethesmallestunusedsequencenumber,thentheinterval[nextseqnum,base+N-1]correspondstopacketthat____..

Acanbesentimmediately.

Bhavealreadybeentransmittedandacknowledged.

Ccannotbeused.

Dhavebeensentbutnotyetacknowledged.

68.WhichofthefollowingaboutTCPisnotcorrect?.

AItisaconnectionlessprotocol.

BPoint-to-pointprotocol.

CReliable,in-orderbytesteamprotocol.

DPipelinedprotocol.

69.WhichofthefollowingaboutTCPisnotcorrect?.

AItisaconnectionlessprotocol.

Bfullduplexdatatransferprotocol.

Cconnection-orientedprotocol.

Dflowcontrolledprotocol.

70.Themaximumamountofdatathatcanbegrabbedandplacedinasegmentislimitedbythe____..

AMaximumsegmentsize(MSS).

BMTU.

CSequencenumber.

DChecksum.

71.TheMSSistypicallysetbyfirstdeterminingthelengthofthelargestlink-layerframethatcanbesentbythelocalsendinghost(theso-called____),andthenwillfitintoasinglelink-layerframe..

AMaximumsegmentsize(MSS).

BMTU.

CSequencenumber.

DChecksum.

72.TheMSSisthemaximumamountof____layerdatainthesegment,notthemaximumsizeoftheTCPsegmentincludingheaders..

AApplication.

BTransport.

CNetworking.

DLink.

73.Whichofthefollowingfieldisnotusedforconnectionsetupandteardown?.

ASequencenumber.

BTST.

CSYN.

DFIN.

74.____isthebytestreamnumberoffirstbyteinthesegment..

ASequencenumber.

BACKnumber.

CChecksum.

Dportnumber.

75.____isthebytesequencenumbersofnextbyteexpectedfromotherside..

ASequencenumber.

BACKnumber.

CChecksum.

Dportnumber.

76.BecauseTCPonlyacknowledgesbytesuptothefirstmissingbyteinthestream,TCPissaidtoprovide____acknowledgements..

ACumulative.

BSelective.

CSingle.

DNegative.

77.Fastretransmitmeansinthecasethat____duplicateACK-sarereceived,theTCPsenderresendsegmentbeforetimerexpires..

A3.

B4.

C5.

D6.

78.TCP____meanssenderwon’toverflowreceiver’sbufferbytransmittingtoomuch,toofast..

AFlowcontrol.

BCongestioncontrol.

CReliabledatatransfer.

DConnection-orientedservice.

79.TCPprovidesflowcontrolbyhavingthesendermaintainavariablecalledthe____..

AReceivewindow.

BCongestionwindow.

CSlidingwindow.

Dbuffer.

80.HowdoesTCPsenderperceivecongestion?.

ATimeout.

B3duplicateACK-s.

CBothAandB.

DNoneofabove.

81.Transportprotocolsrunin____..

AServers.

BClients.

CRouters.

DEndsystems.

82.WhichofthefollowingservicesisnotprovidedbyTCP?.

ADelayguaranteesandbandwidthguarantees.

BReliabledatatransfersandflowcontrols.

CCongestioncontrols.

DIn-orderdatatransfers.

83.WhichservicedoesUDPnotprovide?.

Amultiplexing.

Bde-multiplexing.

Cerror-detection.

Derror-correction.

84.TherearethreemajoreventsrelatedtodatatransmissionandretransmissionintheTCPsender,whichoneisnotinit?.

Adatareceivedfromapplicationabove.

Bde-multiplexingsegment.

Ctimertimeout.

DACKreceipt.

85.WhichofthefollowingapplicationsnormallyusesUDPservices?.

ASMTP.

BStreamingmultimedia.

CFTP.

DHTTP.

86.WhichofthefollowingaboutTCPconnectionisnotcorrect?.

AItisabroadcastconnection.

BItisapoint-to-pointconnection.

CItisapipelinedconnection.

DItisafullduplexconnection.

87.TheSYNsegmentisusedfor____..

ATCPconnectionsetup.

BTCPflowcontrol.

CTCPcongestioncontrol.

DClosingaTCPconnection.

88.Whichservicehelpspreventtheinternetfromenteringastateofgridlock?.

Areliabledatatransfer.

Bflowcontrol.

Ccongestioncontrol.

Dhandshakingprocedure.

89.TheInternet’s_____isresponsibleformovingpacketsfromonehosttoanother..

Aapplicationlayer.

Btransportlayer.

Cnetworklayer.

Dlinklayer.

Inthefollowingapplications,whichoneisabandwidth-sensitiveapplication?.

AE-mail.

Bwebapplication.

Creal-timeaudio.

Dfiletransfer.

91.Inthefollowingapplications,whichoneusesUDP?.

AE-mail.

Bwebapplication.

Cfiletransfer.

DDNS.

92.Inthefollowingfourdescriptions,whichoneiscorrect?.

AIfonehost’stransportlayerusesTCP,thenitsnetworklayermustusevirtual-circuitnetwork..

BDatagramnetworkprovidesconnectionservice.

CThetransport-layerconnectionserviceisimplementedintherouter.

DThenetwork-layerconnectionserviceisimplementedintherouteraswellasintheendsystem..

____isaspeeding-matchingservicematchingtheratewhichthesenderissendingagainsttherateatwhichthereceivingapplicationisreading..

Acongestioncontrol.

Bflowcontrol.

Csliding-windowcontrol.

Dvariablecontrol.

94.InthefollowingfourdescriptionsaboutRcv-Window,whichoneiscorrect?.

AThesizeoftheTCPRcvWindowneverchangesthroughoutthedurationoftheconnection.

BThesizeoftheTCPRcvWindowwillchangewiththesizeoftheTCPRcvBuffer.

CThesizeoftheTCPRcvWindowmustbelessthanorequaltothesizeoftheTCPRcvBuffer.

DSupposehostAsendsafiletohostBoveraTCPconnection,thenumberofunacknowledgedbytesthatAsendscannotexceedthesizeofthesizeoftheRcvWindow..

95.Thereare6flagfields.Whichoneistoindicatethatthereceivershouldpassthedatatotheupperlayerimmediately?.

APSH.

BURG.

CACK.

DRST.

96.SupposetheTCPreceiverreceivesthesegmentthatpartiallyorcompletelyfillsingapinreceiveddata,itwill____..

AimmediatelysendACK.

BimmediatelysendduplicateACK.

Cwaitsometimeforarrivalofanotherin-ordersegment.

Dsendsinglecumulative.

97._____imposesconstrainontherateatwhichaTCPsendercansendtrafficintothenetwork..

Aslidingwindow.

Bcongestionwindow.

Creceivewindow.

Dvariablewindow.

98.Flowcontrolandcongestioncontrolaresameatthattheyalllimittherateofthesender,butdifferinthat____..

AflowcontrollimitsitsratebythesizeofRcvWindow,butcongestioncontrolbythetrafficonthelink.

BcongestioncontrollimitsitsratebythesizeofRcvWindow,butflowcontrolbythetrafficonthelink.

Cflowcontrolmainlyisaccomplishedbythesender,butcongestioncontrolbythereceiver..

Dflowcontrolmainlyisaccomplishedbythereceiver,butcongestioncontrolbythelink..

99.Thisjobofdeliveringthedatainatransport-layersegmenttothecorrectsocketiscalled____..

Amultiplexing.

Bde-multiplexing.

Cforwarding.

Drouting.

100.IfwedefineNtobethewindowsize,basetobethesequencenumberoftheoldestunacknowledgedpacket,andnext-seq-numtobethesmallestunusedsequencenumber,thentheinterval[base,nextseqnum-1]correspondstopacketthat____..

Acanbesentimmediately.

Bhavealreadybeentransmittedandacknowledged.

Ccannotbeused.

Dhavebeensentbutnotyetacknowledged.

101.____arethetwotypesoftransportservicesthattheInternetprovidestotheapplications..

ATCPandUDP.

Bconnection-orientedandconnectionlessservice.

CTCPandIP.

Dreliabledatatransferandflowcontrol.

102.Inthefollowingdescriptionsaboutpersistentconnection,whichoneisnotcorrect?.

ATheserverleavestheTCPconnectionopenaftersendingaresponse.

BEachTCPconnectionisclosedaftertheserversendingoneobject.

CTherearetwoversionsofpersistentconnection:withoutpipeliningandwithpipelining.

DThedefaultmodeofHTTPusespersistentconnectionwithpipelining.

103.ThefieldofLengthinUDPsegmentspecifiesthelengthof____..

AtheUDPsegment,notincludingtheheader.

BtheUDPsegment,includingtheheader.

CtheUDPsegment’sheader.

DtheLengthfield.

104.InTCPsegmentheader,whichfieldcanimplementthereliabledatatransfer?.

Asourceportnumberanddestinationportnumber.

BsequencenumberandACKnumber.

Curgentdatapointer.

DReceivewindow.

105.InthefollowingfourdescriptionsaboutTCPconnectionmanagement,whichoneisnotcorrect?.

AEitherofthetwoprocessesparticipatinginaTCPconnectioncanendtheconnection.

BIftheFINbitissetto1,itmeansthatitwantstoclosetheconnection.

CInthefirsttwostepofthethree-wayhandshake,theclientandserverrandomlychooseaninitialsequencenumber.

DInthethreesegmentsofthethree-wayhandshake,theSYNbitmustbesetto1.

106.SupposehostAsendstwoTCPsegmentsbacktobacktohostBoveraTCPconnection.Thefirstsegmenthassequencenumber42,andthesecondhassequencenumber110.Ifthe1stislostand2ndarrivesathostB.Whatwillbetheacknowledgmentnumber?.

A43BACK42.

C109DACK110.

.

.

.

ConsidersendinganobjectofsizeO=500,000bytesfromservertoclient.LetS=500bytesandRTT=0.2s.Supposethetransportprotocolusesstaticwindowswithwindowsize5.Foratransmissionrateof100Kbps,determinethelatencyforsendingthewholeobject.RecallthenumberofwindowsK=O/WS),andthereisK-1stalledstate(thatisidletimegaps)..

.

.

2.ConsiderthefollowingplotofTCPcongestionwindowsizeasafunctionoftime..

14

180

26

300

0

2

6

4

8

10

12

16

20

22

240

28

32

Congestio