2024-2025第二学期计算机网络试卷1A

天津理工高校考试试卷

2024-2025学年度第2学期

《计算机网络技术》期末考试试卷

课程代码：()60()100试卷编号:程A命题日期：程代年5月2()日

答题时限：120分钟考试形式：闭卷笔试

得分统计表：

题号

―-三四五

PARTI:SingleChoice(1pointperquestion-total:20points)

Instructions:Selectoneofthelettersbesidethechoicethatisthebestanswerforeachquestion.

得分

Q1234567891011121314151617181920

A

1.WhichofthefollowingservicesdoestheInternetnetworklayerprovidefortheInternettransport

layer?

a)In-orderdeliveryofdatasegmentsbetweenprocesses

b)Besteffortdeliveryofdatasegmentsbetweencommunicatinghosts

c)Multiplexinganddemultiplexingoftransportlayersegments

d)Congestioncontrol

2.ThemaintaskoftheInternet'sDomainNameSystem(DNS)isto:

a)TranslateportnumberstoIPaddresses

b)SpecifythestandardsforInternetdomainnames

c)Provideanauthorityforregisteringdomainnames

d)TranslatemnemonicnamestoIPaddresses

3.RDT3.()'sreceiverFSMissameto:

a)RDT1.0b)RD12.1c)RD42.2d)RDT2.0

4.TheTransmissionControlProtocol(TCP)provideswhichofthefollowingservices?

a)End-to-endstationaddressing

b)Applicationmultiplexing

c)Internetworkrouting

d)Mediumaccesscontrol(MAC)

5.Whenadestinationhosttransportlayerreceivesdatafromthenetworklayer,itunambiguously

identifiestheappropriateprocesstopassthedatatobyusingatripletconsistingof:

a)Sourceport#,destinationIPaddress,andsourceIPaddress

b)Destinationport#,sourceport#,processID#

a)Destinationport#,sourceport#,destinationIPaddress

c)Destinationport#,sourceport#,sourceIPaddress

6.Giventhattherequestedinformationisnotavailableatanyintermediatedatabases,a

non-iteratedDNSqueryfromarequestinghostwouldfollowthepath:

a)Rootnameserver,localnameserver,authoritativenameserver

b)Authoritativenameserver,rootnameserver,hostnameserver

c)Localnameserver,rootnameserver,localnameserver,authoritativenameserver

a)Localnameserver,rootnameserver,authoritativenameserver

7.Fromthelistbelow,selecttheitemsfoundintheTCPsegmentstructurethatarenotfoundin

theUDPsegmentstructure'.

a)ApplicationGeneratedData

b)DestinationPort#

c)SourcePort#

a)Sequence#

8.Selectthefouressentialsteps,brieflydescribed,forterminatingaTCPconnectionbetweena

clientandaserver,assumingihattheinitiatinghostistheclient:

(1)ClientsendsTCPsegmentwithACKOandfinalsequencenumber

(2)ClientsendsTCPsegmentwithFIN=1andgoesintoFIN_WAITstate

(3)ServersendsTCPsegmenttoACKtheclient'sFINrequestandentersCLOSEWAIT

state

(4)ServersendsTCPsegmentwithFIN=0

(5)ServersendsTCPsegmentwithFIN=1

(6)ClientsendsTCPsegmentwithtoACKserver'sFINandenterssecondFINWAITstate

(7)ClientsendsTCPsegmentwithFIN=0

a)2,3,5,6b)5,1,2,3c)1,3,5,7d)2,3,4,6

9.TheRIProutingprotocolisbasedonanalgorithmthatis:

a)Basedoninformationreceivedonlyfromlink“neighbors”

b)Alinkstatealgorithm

c)AnOSPFalgorithm

d)Acentralizedroutingalgorithm

10.Whencompensatingforlinkcostchangesinthedistancevectoralgorithm,itcangenerallybe

saidthat:

a)Increasedcostsarcpropagatedquickly,i.c.,4tbadnews^travelsfast

b)Decreasedcostsarepropagatedrapidly,i.e.,“goodnews,,travelsfast

c)Decreasedcostsdonotconverge

d)Noneoftheabove

11.TwoimportantreasonsthattheInternetisorganizedasahierarchyofnetworksforthe

purposesofroutingare:

a)Leastcostandmaximumfreecircuitavailability

b)Scaleandadministrativeautonomy

c)Messagecomplexityandspeedofconvergence

d)Linkcostchangesandlinkfailure

12.Withanexteriorroutingprotocol,whichofthefollowingissuesgenerallydominatesthe

routingdecisions?

a)GeographicaldistancebetweenAS's

b)Policy

c)NumberofAS'straversed

d)CurrentcongestionlevelsintheAS's

13.ThehostcomponentofaCIDRaddressoftheformcancontainaddressesfor:

a)2(32'22)hosts(minus<€special^^hosts)

b)512hosts(minus"special"hosts)

c)dtimes22hosts

d)10hosts(minus“special”hosts)

14.AsanIPdatagramtravelsfromitssourcetoitsdestination:

a)thesourceIPaddressischangedateachroutertoidentifythesendingrouter

b)therouterusesthedestinationIPaddresstoconsultitsroutingtable

c)therouterdocsnotusetheIPaddressesinthedatagram

d)thedestinationIPaddressischangedateachroutertoreflectthenexthop

15.Fromthelistbelow,choosethebitpatternwhichcouldbeavalidgeneratorvaluefortheCRC

code(R)11010:

a)1110

b)011010

c)100101

d)10011

16.Theprimaryfunctionoftheaddressresolutionprotocol(ARP)thatresidesinInternethosts

androutersis:

a)ToprovideLANrouterfunctions

b)TotranslatebetweenLANaddressesandphysicalinterfaceaddresses

c)TotranslatebetweenIPaddressesandLANaddresses

d)TocalculatetheshortestpathbetweentwonodesonaLAN

17.Considersendinga1300byteIPv4datagramintoalinkthathasanMTUof500bytes:

a)Threefragmentsarecreated.

b)Fourfragmentsarecreated.

c)Threefragmentsarecreatedwithoffsets0,500100()

d)Thelastfragmentconsistsofexactly300bytesofdatafromtheoriginaldatagram

18.SupposeoneIPv6routerwantstosendadatagramtoanotherIPv6router,butthetwoare

connectedtogetherviaaninterveningIPv4router.Ifthetworoutersusetunneling,then:

a)ThesendingIPv6routercreatesanIPv4datagramandputsitinthedatafieldofanIPv6

datagram.

b)ThesendingIPv6routercreatesoneormoreIPv6fragments,noneofwhichislarger

thanthemaximumsizeofanIPv4datagram.

c)ThesendingIPv6routercreatesanIPv6datagramandputsitinthedatafieldofanIPv4

datagram.

d)ThesendingIPv6routercreatesanIPv6datagramandinterveningIPv4routerwillreject

IheIPv6datagram

19.WhichofthefollowingwasanimportantconsiderationinthedesignofIPv6

a)fixedlength40-byteheaderandspecifiedoptionstodecreaseprocessingtimeatIPv6

nodes

b)128-bitaddressestoextendtheaddressspace

c)differenttypesofservice(flows)defined

d)alloftheabove

20.Anetworkbridgetableisusedtoperformthefollowing:

a)MappingMACaddressestobridgeportnumbers

b)ForwardingframesdirectlytooutboundportsforMACaddressesithandles

c)Filtering(discarding)framesthatarenotdestinedforMACaddressesithandles

d)Alloftheabove

PARTII:True/False(1pointsperquestion-total:15points)

Instructions:Markthesymbol(forTrue)ifthestatementiscorrect,orthesymbol(fbr

False)ifthestatementisincorrect.

得分

Q123456789101112131415

A

1.TheInternet'sTransportLayerprotocolprovidesreliabledatatransferbetweenendsystems.

2.NetworksshouldbedesignedsuchthattheTrafficIntensityvalueforeachnetworknodeisless

than1.

3.ThemaximumsizeofasingleUDPsegmentislimitedto2I6-1bits.

4.FTPusestwoseparateTCPconnections,onetoport20andonetoport21,andissaidtosendits

commandsUoutofband^^.

5.DuringthefirststepofaTCPconnectionhandshakebetweenaclientandaserver,theserver

receivesaTCPsegmentwithanullsequencenumberandtheSYNbitsetto1.

6.TCPcongestioncontrolisdesignedtopreventbufferoverflowinnetworkend-systems.

7.Duetothecharacteristicsofitscongestionavoidancealgorithm,TCPcanbesaidtobea“fair”

protocolwithregardtosharingavailablebandwidthamongusersofacommontransmissionlink.

8.IntheInternet,interiorroutersinthesameautonomoussystemexecutethesamerouting

algorithmtocomputeroutingpaths.

9.AHlinklayerprotocolsthatsupportIPhavethesameframestructure(i.e.,lengthofframe,

numberandlengthofheaderfields).

10.Routerssometimesusetransportlayerprotocols,suchasTCPorUDP,toexchangerouting

tabicinformationwitheachother.

11.AnynodeintheIPnetworkdefinedbywouldberequiredtohaveanIPaddressoftheform.

12.PureAlohaismoreefficientthanSlotted-Aloha.

13.Theentriesinabridgetableneedtobeconfiguredbythenetworkadministrator.

14.Layer-2switchescanbeusedtoisolateoneLANsegment'scollisiondomainfromthatof

anotherLANsegment.

15.TheTimeDivisionMultiplexing(TDM)channelpartitioningprotocolisappealingbecauseit

eliminatescollisionsandisperfectlyfairwithregardtobandwidthavailability.

PARTHI:Brieflyanswereachofthefollowingquestions.(1pointsperquestion-

total:20points)

得分

1.Explainthedifferencebetweenconnection-orientedmessagingserviceandconnectionless

messagingservice.

2.Explainthedifferencebetweengo-back-Nandselectiverepeat.

3.Wherecanqueuingoccurinarouter?Brieflyexplaintheconditionsthatleadtosuch

queuing.

4.Satellitelinksoftenexhibithighpropagationtimesandlowtransmissionspeed.Whatdoes

thismean?

5.ThedifferencebetweenUDPandIPpacketsisminimal.Whyshouldn'tapplicationsuseIP

directly?

6.Cantwocomputersthathaveadifferentimplementationofthesameprotocolexchange

messages?Explainyouranswer.

7.Whatarethedifferencesbetweenroutingandforwarding?Brieflyexplaineachofthem.

8.Brieflyexplaintheformula<4lastBytcSent-lastByteAcked<iiiiii{CongWin,Rc、，Wiii}”.If

necessary,youcandrawafiguretodescribeyouranswer.

9.EthernetfollowsaCSMA/CDprotocolscheme.Explainhowthisschemeworks.

10.Foraslidingwindowprotocol,itisnecessarytohavethewindowsizeatmosthalfofthe

rangeofsequencenumbers.Why?

PARTIV:Answereachofthefollowingquestions.(Total:55points)

得分

1.(total:6points)Considerthenetworkshownbelow.RunDijkstra'salgurilhm(ocompute

theshortestpathsfromAtoallothernodesinthenetwork.Whileselectingthenextnode,if

severalnodeshavethesamemincost,selecttheonewithlowestid,(e.g.,ifBandDhavethe

samemincost,thenselectB).

Determinetheroutingtable(destination,next-node,andcost)atnodeA.

DestinationNextNodeCost

B

C

D

E

F

G

I

J

K

L

M

2.(total:6points)Renocongestioncontrolalgorithm.

ConsiderTCPReno(theonethatusesbothtimeoutand3duplicateACKstodetectpacketlosses).

RememberthereceiversendscumulativeACKwheneverasegmentisreceivedandassumethatour

TCPimplementationdiscardsout-of-ordersegments,soasinGo-Back-N,thesendershould

re-transmitallpacketsstartingfrombasewhenapacketlossisdetected.Remembercongestion

windowneedstobeadjustedbeforeretransmission.

Aserverapplicationhas26TCPsegments(packets)(thatarenumberedas1,2,3...26)tosendto

thereceiversite.Assumethatthesenderstartedfromslowstartwithacongestionwindowof1and

continuedaccordingtoTCPRenocongestioncontrolalgorithm.TheinitialThresholdvaluewas4.

ThetimeoutdurationatthesenderissettoRTT.AssumethatthesendersendsanumberofTCP

segmentsandreceivesallACKsjustbeforethenextRTT(ignorethetimebetweenback-to-back

sentsegments).Finally,assumethat15lhand21stsegmentsgotlostduringtheirfirsttransmission.

Now,byusingtheaboveinformation,yourtaskistocompletetheblankentriesinthebelow

tableuntilallthesegmentsaresentandalltheACKsaresuccessfullyreceived.Ifyouwant,youcan

usethechartbelowtoworkoulyoursolutionbeforefillinginthetablebelow.

TABLE

Congestion

RTTThresholdSegmentsthataresent

Window

0411

1422,3

2

3

4

5

6

7

8

9

1()

11

3.(5points)Matchthetermswiththeirbestcorrespondingdefinitionorconcepts.Jointhem

togetherwithlines.

SYN,ACKAlayer4protocol

SpanningTreeAlgorithmOneoftheirprimaryjobsinvolvesRFCs

repeaterTechniquestoefficientlyuseIPaddresses

IETFThismodellacksasetupandteardownphase

VLSM,CIDRThislayer2technologyhelpspreventbridgeloopsin

EthernetLANsandalsointokenringLANs

connectionlessYoumightthislayer2technologyintokenringLANs,

butnotinEthernetLANs

Full-duplexSomethingyoumightfindinthe3-wayhandshake

UDPAnexampleofawirelinktechnology

SourceroutebridgingTheabilitytotalkandlistenatthesametime

OpticalfibercablingThisdevicemovesbitsfromonedatalinknetworkto

anotherwithoutinspectingtheframe'scontents

4.(total:8points)Cachinganddelays.

Considerthenetworksshowninthefigurebelow.TherearetwousermachinesmLaand

m2.ainthenetworka.Supposetheuseratml.atypesintheURLb

7bigfile.htmintoabrowsertoretrievea1Gbit(100()Mbit)filefromb.

Authoritative

DNSserver

for

a)(5points)ListthesequenceofDNSandHTTPmessagessent/receivedfrom/bymLaaswell

asanyothermessagesthatleave/entertheanetworkthatarenotdirectlysent/receivedby

mLafromthepointthattheURLisenteredintothebrowseruntilthefileiscompletely

received.Indicatethesourceanddestinationofeachmessage.YoucanassumethateveryHTTP

requestbyml.aisfirstdirectedtotheHTTPcacheinaandthatthecacheisinitially

empty,andthatallDNSrequestsareiteratedqueries.

b)(3points)Nowassumethatmachinem2.amakesarequesttoexactlythesameURLthat

ml.amade.ListthesequenceofDNSandHTTPmessagessent/receivedfrom/bym2.a

aswellasanyothermessagesthatleave/cntcrtheanetworkthatarcnotdirectly

sent/receivedbym2.afromthepointthattheURLisenteredintothebrowseruntilthefileis

completelyreceived.Indicatethesourceanddestinationofeachmessage.[Hint:makesureyou

considercachinghere]

5.(total:11points)Addressing,andfollowingthedata

Considerthesimplenetworkshownbelow:

1.111.1II

RI_____R2

a)WritedownanIPaddressforallinterfacesatallhostsandroutersinthenetwork.TheIP

addressesforAandEareasgiven.YoushouldassignIPaddressessothatinterfacesonthesame

networkhavethesamenetwork-partoftheirIPaddress.Indicatethenumberofbitsinthe

nelwork-partofthisaddress.

BRI

CR2

D__1________________1

b)Choosephysicaladdresses(LANaddresses)foronlythoseinterfacesonthepathfromAtoE.

AE

BRI

CR2

D

Cantheseaddressesbethesameasinparta)?Why?

c)NowfocusontheactionstakenatboththenetworkanddatalinklayersatsenderA,the

interveningrouter,anddestinationEinmovinganIPdatagramfromAtoE:

①HowdoA,EandtherouterdeterminetheIPaddressesneededfortheIPdatagram?

@What,specifically,aretheaddressesintheIPdatagramthatflowsfromAtotherouter?

SourceIPDestinationIP

What,specifically,aretheaddressesintheIPdatagrairthatflowsfromtheroutertoE.?

SourceIPDestinationIP

③WhatareIhreeolherfieldsfoundinanIPdatagram?

®HowdoA,Eandtherouterdeterminethephysical