南邮《专业英语（理工）》综合习题册2023 .10期末复习题

南京邮电大学高等函授《专业英语（理工）》综合练习习题与解答南京邮电大学继续教育学院2023年10月第一章一、单项选择题1.Thereisaninherentadvantagefor()noisyenvironmentsbychoosingdigitaltransmission.A.toovercome B.togetC.overcoming D.overcome2.AtthereceivingterminalofaPCMsystem,()toseparatethe8-digitsequencesintotheappropriatechannels.A.aPCMamplifierisused B.ademultiplexerisneededC.amultiplexerisneeded D.acoderisused3.Ifthesignalisverylargecomparedtothenoiselevel,then().A.aperfectmessagecantakeplace B.thesignal-to-noiseratioispoorC.itisaterrestrialsystem D.thenoisepowerisstrong4.Intheareaofcommunication,theterm“3G”means().A.thethirdgenerationfixedsystemB.thethirdgenerationmobilesystemC.thethirdgenerationtransmissionsystemD.thethirdgenerationcomputertechnology5.Theshapeoftransmittedsignalismosteasilyaffectedbythenoiseandattenuation().A.introducedbytheequipment B.introducedbytheoperatorC.introducedbythetelephoneset D.introducedbythetransmissionpath6.Thebroadcastmobilenetworks,operatingindenselypopulatedarea,couldbe()byaverysmallnumberofsimultaneouscalls.A.operated B.jamC.operate D.jammed7.TheGSMsystemisbasedon()whichwasfirstproposedasaconceptin1940sbyBellSystemengineersinUS.A.PCMprinciple B.cellularnetworkingprincipleC.SDHprinciple D.computernetworkingprinciple8.Theinterconnectioninthefixedtelephoneserviceisfarmore()thanthatinthemobile.A.complex B.simple C.personal D.convenient9.Thepowerofthecellularsystemwasthatitallowed().A.manycallstakingplace B.channelinterferenceexistingC.frequencyreuse D.roaming10.Scannerandprinterbelongtothe()connectedtoaPC.A.peripherydevices B.inputdevicesC.outputdevices D.internaldevices11.ThetransmissionrateatSTM-1is()Mb/s.A.2048 B.1024 C.622.080 D.155.52212.Aringnetworkisorganizedbyconnectingnetwork()inaclosedloopwithnodelinkedtothoseadjacentontherightandleft.A.nodes B.devices C.system D.systems13.Comparedwithagateway,a“bridge”isusedtolinktwotechnologically()tooneanother.A.similargateway B.similargatewaysC.similarnetworks D.similarhardware14.ALANisadatacommunicationsystem()allowsanumberofindependentcomputerstocommunicatewitheachother.A.which B.what C.who D.it15.()youneedtoknowisthatyoucanexchangemessagewithothercomputersontheInternet.A.Where B.Which C.What D.That二、词汇互译16.software17.coder18.multiplexing19.amplification20.addressing21.gateway22.algorithm23.pixel24.specification25.antenna26.subring27.graded-index28.timeslot29.accessnetwork30.alarmingsignal31.软交换32.蜂窝33.鼠标34.容量35.点对点协议三、缩略语翻译36.ADSL37.TCP38.PSTN39.SDH40.FDMA41.DSP42.DSLAM四、阅读理解Signalingisthemeansusedtoestablishandcontroltelephonecalls.Itincludessignalsfromterminals(stationsignaling),toandfromswitchingcenters(registersignaling),andalsosignalsbetweenswitchingcenters(linesignaling).Signalsarecarriedbythelineandlinktransmissionequipment,andtheswitchingcenters.Signalingalsoincludesthetonesandrecordedmessageswhichareusedtoindicatetheprogressofcallsthroughthetelecommunicationsnetwork.Therearealsosignalsinternaltoaswitchingsystemwhichconveysinformationandcommandstoandfromvariouspartsofthesystemandoperatingandadministrationsignals.Themodesofsignalingincludethefollowing:(1)DirectCurrent(直流)Signaling.Inthedirectcurrentsignalingmethod(loop-disconnectsignaling),asignalingcodeisderivedfromthedurationanddirectionofthecurrentflowingthroughaloop.Thisloopincludesthecustomer'sequipmentandthelinetransmissionequipmentanditsswitchingcenterinterface.Directcurrentloopsignalingisalsousedwithtrunktransmissionequipmentofthewiretype.(2)AlternatingCurrentSignaling.Alternatingcurrentsignalingisbasedonsignalsofdifferentfrequencyeitherinthesamebandwidth(inband)asthespeechtransmissionpath(300to3400Hz)oratalower.<oratahigher>3400Hz,frequency(outband).(3)DigitalSignals.Digitalsignalstaketheformofaseriesofsuccessivepulses,binarysignals,whicharecodedtoproduceasignalingformat.Digitalsignalsmayoccupyaportionofoneofthetineslotsusedforthetransmissionofspeech(inslot)ormayuseadedicatedtimeslot.Signalingmayusethesametransmissionpathasthespeechordatasignalsoritmayuseaseparatechannel.Thefirstcaseiscalledchannel-associatedsignaling,thesecondcaseiscalledcommonchannelsignaling.Commonchannelsignalingnotonlyspeedsthecallsetuptime,butalsoenablessendingmoreinformationaboutthecallinbothdirections.Itisnowbeingappliedmoregenerallyonadisassociatedbasis.Thismeansthatthesignalingbetweenswitchingnodesdoesnotparallelnornecessarilyusethesametransmissionfacilitiesorroutesasthesignalsthatcarrythecallsandmessages.43.Signalingisthe()usedtoestablishandcontroltelephonecalls.A.path B.road C.way D.route44.Signalsare()bythelineandlinktransmissionequipmentandtheswitchingcenters.A.transmitted B.brought C.taken D.converted45.Therearevariouskindsofsignals()establishandcontroltelephonecalls.A.when B.that C.who D.whose46.Somesignalsconvey(传送)()toandfromvariouspartsofthesystem.A.aninformationandacommand B.informationandcommandsC.informationandcommand D.informationsandcommands47.Thecustomer'sequipment,thelinetransmissionequipmentanditsswitchingcenterinterface()intheloop.A.include B.included C.haveincluded D.areincluded48.Thosesignalsarecarried()alowerfrequency.A.with B.in C.on D.at49.Digitalsignalstakethe()ofaseriesofsuccessivepulses.A.shape B.appearance C.form D.size50.Incommonchannelsignaling,moreinformationaboutthecall()inbothdirections.A.issent B.aresend C.issend D.aresent五、句子翻译51.WDM,ontheotherhand,makesitpossibletotransmitalargenumberofwavelengthsusingthesamefiber,effectivelysendinga“rainbow”ofcolors,wheretherewasonlyonecolorbefore.52.Therevolutionofopticalnetworkisjustbeginning,andisadvancingveryswiftlytowardsafurtheronlineworldinwhichbandwidthisessentiallyunlimited,reliable,andlow-cost.53.TheyusethelogicconnectionsofATMnetworklevelwhichinturnmultiplexesandlogicallyroutestheinformationflowasATMcellsgothroughthetransmissionlinkssharedbylogicalconnectionscalledvirtualconnections.54.IPTViscomplementarytoexistingsatellite,cableandterrestrialsystems,althoughinsomecasesitmaybecomeavigorouscompetitortothem.55.Itistimetoraisetheawarenessofbroadcasters,sothattheycanplayamoreactiveroleintheIPTVdevelopments.56.TheInternetisthelargestrepositoryofinformationwhichcanprovideverylargenetworkresources.Thenetworkresourcescanbedividedintonetworkfacilitiesresourcesandinformationresources.Thenetworkfacilitiesresourcesprovideustheabilityofremotecomputationandcommunication.Thenetworkinformationresourcesprovideusallkindsofinformationservices,suchasscience,history,law,education,business,art,andentertainment,etc.TheInternetisyourPC'swindowstotherestoftheworld.DoyouthinkthatyoucanworkwellwithouttheInternet?57.Thepotentialoffiberopticsinotherareasisonlybeginningtoberealized.Fiberopticnetworksforcomputersystemsandofficesarebecomingmoreandmoreprominent(重要的).Inthetelephonesystem,theuseoffiberopticsforinterconnectingcentralofficeswithinametropolitan（大都市）areaandforlowerlevelsinswitchinghierarchyisstillIncreasingrapidly.Fiberlinkstothehomehavebeenusedindemonstrationprojects（示范项目）.Manyobserversbelievethatnationaltelephonesystemswilleventuallybeupgradedtocandlevideobandwidthsbyusingfiberoptics.单项选择题1.C 2.B 3.A 4.B 5.D 6.D 7.B 8.B 9.C 10.A11.D 12.A 13.C 14.A 15.C词汇互译16.软件 17.编码器 18.多路复用 19.放大 20.寻址21.网关 22.算法 23.像素 24.规范，说明25.天线26.子网 27.渐变指数 28.时隙 29.接入网 30.告警信号31.softswitch 32.cell 33.mouse 34.capacity35.pointtopointprotocol缩略语翻译36.不对称数字用户环路 37.传输控制协议38.公共交换电话网 39.同步数字分层（序列）40.频分多址接入 41.数字信号处理42.数字用户线接入复用器阅读理解43.C 44.A 45.B 46.B 47.D 48.D 49.C 50.A句子翻译51.另一方面，WDM使得使用同样的光纤传输很多的波长成为可能，能够有效地发送颜色的“彩虹”，而这以前只有一种颜色。52.光网络的演进刚刚开始,并且正向着未来的带宽无限、可靠低费用的在线世界快速发展。53.它们使用ATM网络层的逻辑连接，当信元经逻辑连接（虚连接）共享的传输链路时，ATM网络层依次对信息流复用并寻找其逻辑路由。54.网络电视是对现有卫星、电缆、地面系统的补充，虽然在某些方面还是它们的有力竞争者。55.该是警醒广播电视服务商的时候了，以便使得他们在发展IPTV过程中起到更加活跃的作用。短文翻译56.互联网是最大的信息库，它提供了极大的网络资源。网络资源可以分为网络设备资源和网络信息资源。网络设备资源向我们提供了远程计算和通信能力。网络信息资源向我们提供了所有种类的信息，如科学、历史、法律、教育、商务、艺术和娱乐等等。互联网是你的个人机通向世界的窗口。你认为没有互联网你能工作得好吗？57.人们对于光纤在其他领域的潜力刚刚开始认识。用于计算机系统和办公室的光纤网络逐渐变得更加重要。在电话系统中，光纤在主要城市地区中心交换局间互联和低级交换中的使用继续迅速增加。入户光缆已经有了示范工程。许多观察家相信，全国电话系统将使用光纤传输视频宽带信号而逐渐升级。第二章一、单项选择题1.Theproblemiseasilyovercomebyspecifyingaframeformat,whereatthestartofeachframeauniquesequenceofpulsesisplaced()thestartoftheframe.A.identify B.soastoidentifyC.foridentify D.identifying2.Thisinterfaceissocalledbecausethetransmittedandthe()dataarenotsynchronizedoveranyextendedperiod.A.receive B.accepting C.accepting D.received3.Serialdatatransmissionsystems()inthetelephone,Morsecode,andeventhesmokesignalonceusedbyNativeAmericans.A.arefindingB.arefound C.willbefound D.tobefound4.ThetermATMincommunicationis().A.automatictransmissionmedia B.automatictakingmoneyC.asynchronoustransfermode D.asymmetricterminalmodule5.Thefallingedgeofthestartbittriggersthereceiver’slocalclock,which()A.sampleseachincomingbitatitsnominalcenterB.makeupofanewcharacterC.showsachannelerrorD.monitorsthelinelookingforastartbitoranendingbit6.Insimpleterms,3Gservicescombinehighspeedmobileaccess()IP-basedservices.A.withB.in C.into D.on7.WCDMApromises()abenefitofreducedcostforvideohandsets.A.toachieveB.willtake C.achievement D.achieve8.CDMA1Xsupportsbothvoiceanddataservicesover(),andprovidesmanyperformanceadvantagesoverothertechnologies.A.atelephonechannel B.astandard(1X)channelC.avirtualcircuit D.aFDMchannel9.ITUis().A.amultinationalmanufacturer B.amultinationaloperatorC.aninternationalorganization D.akindoftelecomproduct10.Usually,wetalkabout“opticcommunication”andlearnitsfundamentalprinciple.Theword“optical”presents().A.光学 B.光调制 C.光纤 D.光波11.TheMTSOisthe（）ofthecellularmobilesystem.A.importantcircuit C.servicedeviceB.heart D.key12.TheInternetisthelargestrepositoryofinformationinwhichwecangetverylarge().A.networkservices B.networkresourcesC.networkdevices D.networknodes13.Theresearcherswhoproducedthefirstcladglassopticalfibersintheearly1950swerenotthinking()themforcommunication.A.ofusing B.useC.ofuse D.thatuse14.Manyobserversbelievethatinthefuturenationaltelephonesystemswilleventually()handlevideobandwidthsbyusingfiberoptics.A.upgradedto B.beupgradingtoC.beupgradeto D.beupgradedto15.Forinstance，theoriginalCATVnetworksdidnotallowedthetransportationofPOTS；orthePSTNdoesnottransportTVsignals.Here,POTSis().A.plainoldtelephoneservice B.popularoldtelephoneserviceC.plainoperationaltelephoneset D.publicoldtelephoneservice二、词汇互译16.hardware17.decoder18.multiplex19.attenuation20.mapping21.overlay22.downstream23.subnet24.amplifer25.handover26.inlet27.occupy28.laser29.signal-to-noiseratio30.attributesignal31.色散32.解调器33.浏览器34下行链路35.宽带业务三、缩略语翻译36.ITU37.TDMA38.LAN39.FTP40.MSC41.NGN42.HDTV四、阅读理解Passage1TheGSMsystemisbasedonacellularcommunicationsprinciplewhichwasfirstproposedasaconceptinthe1940sbyBellSystemengineersintheUS.Theideacameoutoftheneedtoincreasenetworkcapacityandgotroundthefactthatbroadcastmobilenetworks,operatingindenselypopulatedareas,couldbejammedbyaverysmallnumberofsimultaneouscalls.Thepowerofthecellularsystemwasthatitallowedfrequencyreuse.Thecellularconceptisdefinedbytwofeatures:frequencyreuseandcellsplitting.Frequencyreusecomesintoplaybyusingradiochannelsonthesamefrequencyincoverageareasthatarefarenoughapartnottocauseco-channelinterference.Thisallowshandlingofsimultaneouscallsthatexceedthetheoreticalspectralcapacity.Cellsplittingisnecessarywhenthetrafficdemandonacellhasreachedthemaximumandthecellisthendividedintoamicro-cellularsystem.Theshapeofcellinacellularsystemisalwaysdepictedasahexagonandtheclustersizecanbeseven,nineortwelve.43.Theshapeofcellinacellularsystemisalwaysdescribedasa（）A.octagon B.hexagon C.triangle D.quadrate44.Inthe1940s,broadcastmobilenetworkswhichoperatesindenselypopulatedareascouldbejammedbyaverysmallnumberof()calls.A.simplifiedB.theoreticalC.improved D.simultaneous45.Cell()isnecessarywhenthetrafficdemandonacellhasreachedthetopandthecellisthenseparatedintoanumberofsmallerareas.A.increasingB.reducing C.splitting D.demanding46.Whatarethefeaturesofthecellularconcept?()A.frequencyreuseandcellsplittingB.spectrumallocationC.handoverwhennecessaryD.theallocationofuplinksPassage2TheSDHStandardsarebasedontheprinciplesofdirectsynchronousmultiplexingwhichisthekeytocosteffectiveandflexibletelecommunicationnetworking.Inessence,itmeansthatindividualtributarysignalsmaybemultiplexeddirectlyintoahigherrateSDHsignalwithoutintermediatestagesofmultiplexing.SDHNetworkElementscanthenbeinterconnecteddirectlywithobviouscostandequipmentsavingsovertheexistingnetwork.AdvancednetworkmanagementandmaintenancecapabilitiesarerequiredtoeffectivelymanagetheflexibilityprovidedbySDH.Approximately5%oftheSDHsignalstructureisallocatedtosupportingadvancednetworkmanagementproceduresandpractices.TheSDHsignaliscapableoftransportingallthecommontributarysignalsfoundintoday’stelecommunicationnetworks.ThismeansthatSDHcanbedeployedasanoverlaytotheexistingsignaltypes.Inaddition,SDHhastheflexibilitytoreadilyaccommodatenewtypesofcustomerservicesignalsthatnetworkoperatorswillwishtosupportinthefuture.SDHcanbeusedinalltraditionaltelecommunicationsapplicationareas.SDHthereforemakesitpossibleforaunifiedtelecommunicationnetworkinfrastructuretoevolve.ThefactthatSDHprovidesasinglecommonstandardforthistelecommunicationsnetworkmeansthatequipmentsuppliedbydifferentmanufacturersmaybeinterconnecteddirectly.47.WhatisthebaseoftheSDHStandards?（）A.indirectsynchronousmultiplexingB.directasynchronousmultiplexingC.indirectasynchronousmultiplexingD.directsynchronousmultiplexing48.HowmuchoftheSDHsignalstructureisallocatedtosupportingadvancednetworkmanagementproceduresandpractices?()A.5% B.6% C.7% D.8%49.WhycanSDHhaveobviouscostandequipmentsavingsovertheexistingnetwork?()A.ThecostofSDHNetworkElementsislowerB.SDHNetworkElementscanbedirectlyinterconnectedC.SDHcanbeusedinalltraditionaltelecommunicationsapplicationareasD.SDHcanbedeployedasanoverlaytotheexistingsignaltypes50.Theword“tributary”means().A.hierarchy B.tribunal C.branch D.patch五、句子翻译51.Forthem,IPTVisanentirelynewmultimediaexperienceextendingthebordersofconventionalbroadcasttelevision.52.Second,thedevelopmentofgainequalizationtechniqueshasenabledamuchflatterresponseandallowsanumberoftheseamplifierstobeconnectedinseries.53.Italsocontainsdatalinksprovidingsupervisionlinksbetweentheprocessorandtheswitchandbetweenthecellsitesandtheprocessor.54.Peoplewhohavetouseamobilephoneonbusinesssoonbegantorealizedthattheabilitytophoneanytime,anyplaceinone’spersonalliferapidlybecomesanecessity,notaconvenience.55.ThesecondgenerationismuchdominatedbythestandardfirstsetoutinEuropebythegroupspecialmobile(GSM)committee,whichwasdesignedasaregionalstandardbefore.六、短文翻译56.Whenthetransmitterwishestosenddata,itfirstplacesthelineinaspacelevelforoneelementperiod.ThiselementiscalledthestartbitandhasadurationofTseconds.Thetransmitterthensendsthecharacter,1bitatatime,byplacingeachsuccessivebitonthelineforadurationofTseconds,untilallbitshavebeentransmitted.Thenasingleparitybitiscalculatedbythetransmitterandsentafterthedatabits.Finally,thetransmittersendsastopbitatamarklevelforoneortwobitperiods.Nowthetransmittermaysendanothercharacter.57.BeforeyoucanusetheInternet,youmustchooseawaytomovedatabetweentheInternetandyourPC.Thislinkmaybeahigh-speeddatacommunicationcircuit,alocalareanetwork(LAN),atelephonelineoraradiochannel.Mostlikely,youwilluseaModemattachedtoyourtelephonelinetotalktotheInternet.Naturally,thequalityofyourInternetconnectionandservice,likemanyotherthingsinlife,isdictatedbytheamountofmoneyyouarewillingtospend.一、单项选择题1.B2.D 3.B 4.C5.A 6.A7.A8.B9.C 10.C11.C 12.B 13.A 14.D15.A二．词汇互译16.硬件 17.译码器 18.多路复用器 19.衰减 20.映射21.包层 22.下行流 23.子网 24.放大器 25.切换26.入口 27.占用 28.激光器 29.信噪比 30.支路信号31.dispersion 32.demodulator 33.explorer 34.downlink35.broadbandservice三．缩略语翻译36.国际电联 37.时分多址接入38.局域网 39.文件传输协议40.移动业务交换中心 41.下一代网络42.高清电视四．阅读理解43.B 44.D 45.C 46.A 47.D 48.A 49.B 50.C五．句子翻译51.对于他们来讲，网络电视是一种扩展了传统广播电视领域的全新多媒体52.其次，增益均衡技术的发展可以产生更加平坦的响应，并允许这样一些放大器串联连接。53.它也包含了在处理器与交换机之间以及基站和处理器之间提供监控的数据链路。54.在商业活动中已经使用移动电话的人们开始认识到在个人生活中随时随地打电话不仅仅是方便而且是必须的。55.第二代移动通信标准主要于欧洲的GSM小组委员会，它是作为以前的一个区域性标准。六．短文翻译56.当发送器需要发送数据时，它先将线路置成一个空格电平持续一个单元时间。这个单元被称为起始比特并具有T秒时长。发送器然后发送字符，一次一个比特，通过将每个有效比特在线路上置为T秒时长，直至所有比特被发送。然后一个奇偶校验比特被计算并在数据比特之后发送。最后，发送器以标记电平值发送终止比特，时长为一到二个比特周期。现在，发送器就可以发送另外字符了。57.在使用Internet之前，必须选择一种方法在你的PC机和Internet之间传送数据。这种连接的链路可以是高速数据通信电路、局域网(LAM)、电话线路或无线信道。最有可能的是，你使用Modem连到电话线上与Internet对话。当然，像生活中许多其他事物一样，与Internet连接和服务的质量是由你所花钱的数量决定的。第三章一、单项选择题1.WhenthedatalinkconnectsaCRTterminaltoacomputer,()problemsarises.astheterminalisitselfcharacteroriented.A.many B.afew C.alotof D.few2.TheOSIreferencemodelallowsyou()thenetworkfunctionsthatoccurateachlayer.A.toview B.view C.watching D.viewed3.Thedatalinklayerprovidesthetransitofdataacrossaphysicallink.Insodoing,thedatalinklayerisconcerned()physicaladdressing,networktopology,errordetectionandsoon.A.at B.in C.,with D.to4.Asthosecompaniesrealizedtheycouldsavemoneyandgainproductivitybyusingnetworkingtechnology,they()A.theyunderstoodthereweresomeproblemsB.addednetworksandexpandedexistingnetworksC.didnotdeveloptheInternetD.stillusedtheoldproductsandoff-linecomputers5.Thelitter“S”intheword“ADSL”means()A.system B.subscriber C.synchronous D.symmetric6.InSDHtransmissionring,thelowestspeedofthedatais()Mb/s.A.32 B.64 C.155.522 D.10247.Theswitch,()circuitswitch,havenocapabilityofstoringuser’sdataontheirwaytothedestination.A.called B.calling C.callD.thatcalled8.Thecircuitissetupbyaspecialsignalingmessage()findsitswaythroughthenetwork,seizingchannelsinthepathasitproceeds.A.who B.where C.one D.that9.Theprincipleofpacketswitchingis()thatofcircuitswitching,whichmaybethoughtofconnectionless-oriented.A.thesameas B.thesameto C.similarto D.differentfrom10.Theheaderofmessagecontainsinformationregarding();thechecksumisusedforerrorcontrolpurposes.A.thetexttobetransmittedB.thesourceanddestinationaddressesC.thevoicechannelsD.manypacketsbetweencomputers11.Itisgrowingsoquicklythatnobodycansay()howmanyusesnow“OntheNetwork”.A.exactly B.exact C.slow D.slowly12.Dataratesforinstalledfiberopticsystemshaverecentlymovedintothegigabitper()range.A.hour B.minute C.seconds D.second13.InGSMsystem,everycell（）theallocatedfrequencybandindifferentgeographiclocations.A.uses B.reusing C.reuses D.use14.TheTDMAmobiletelephonesystemoperatesinabursttransmissionmodewith124ormoreradiochannelsinthe900MHzor1800MHzband.Thewordburstmeans()A.manybits B.manybauds C.datapacket D.digitalsignal15.ThetermISDNwasfirstdefinedwithintheCCITTin1972.Itreferredtoanetworkprovidingend-to-enddigitalconnectivityforarangeofservices.Thewordconnectivitymaybereplacedby()A.connection B.connect C.transmissionD.controlling二、词汇互译16.uplink17.satellite18.synchronous19.overhead20.cabling21.noise22.audio23.subprogram24.duplex25.multitone26.phase27.response28.burst29.video-on-demand30.virtualpath31.频谱32.模拟的33.路由器34.传输时延35.微蜂窝系统三、缩略语翻译36.DXC37.CDMA38.WLAN39.WDM40.BSC41.SDH42.PCM四、阅读理解Let'sdiscusssomethingabout“switching”.Inapacketswitchingnetworkmessagesaresubdividedintopacketswithapre-establishedsize,prefaced(作为…的开始)withtheappropriateaddressinformation.Thoughthissystememploysstore-and-forwardprinciples,packetscanbetransmittedwithaminimumofdelay.Highthroughputcanbeachievedformulti-packetsoverseveralcircuits.Networknodesmayperformmorefunctionthansimpleroutepacketstotheintended(预设的)receiver.Theycanalso:---Checkthatpacketsarriveinthecorrectsequence,withouttransmissionerrororloss.---Choosethebestroutethroughthenetworkaccordingtocurrenttrafficloadingoflinks.---Controlflow,andsoallowslowandfastdevicestobeconnectedwithoutlossofdata.Thismethodiswellmatchedtothepatternofdatacommunicationtrafficanditoffershighreliability,highlineutilization,highflexibility,andthepossibilityofspeedconversion.Packetswitchingcombinesthespeedofcircuitswitchingwiththeeconomyofmessageswitching.Thismeansthatalowercostnetworkcanbedesignedforthesametrafficvolumes,butstoragebeforeforwardingisbriefenoughtoallowpracticallyinstantaneous(即刻)transferand.consequently,interactiveuse.Themainadvantageofpacketswitchingovertheothertelecommunicationtechniquesare:---Improvedlineutilizationbyinterleavingpacketsassociatedwithdiffercalls,takingadvantageofsilence(静音)inindividualcalls.---Possiblespeedandprocedureconversion(转换),permittinginter-communicationbetweendifferentterminaltypes,andadaptationtoevolvingtechnologies.---Serviceofahighquality,providingautomaticcorrectionoftransmissionerrorsandreconfigurationwithoutdatalossintheeventofabreakdown.Themostimportanttaskwhichapacketswitchingnodecarriesoutistodecidewhichwayapacketwillflowthroughamesh(网状)network(throughwhich,ingeneral,thereareatleasttwopossibleroutesbetweenanytwonodes).Therearetwotypesofpacketswitchingroutingconcepts:Apacketswitchingnetworkusingthevirtualcircuitroutingtechniquesetsupalogicalpathorvirtualcircuitforthedurationofthecommunication.Inthiscaseafixedrelationshipbetweenthevirtualcircuitandthephysicalcircuithastobecommunicationlink.Allpacketsfollowthesamepath,makingflexibleroutingduringthedurationofacallimpossible.Whendatagram(数据报)routingisapplies,theroutethateachpacketfollowsischosenindependentlyofthatofalltheprecedingpackets.Byapplyingdynamic(动态的)routingtoeachpacket,thetrafficflowcanbeconstantlyspreadoutandsoensurethatnetworkresourcesareusedmoreefficiently.Thisconsiderablysimplifiesthetaskoftheintermediate(中间的)networknodes,astheythenonlyhavetoperformaswitchingfunction.Theresultisthatnofixedrelationshipbetweenthephysicalcircuitandthevirtualcircuithastobeestablishedandmaintained.43.Thearticlemainlytalksabout:()A.transmissiontechniques B.circuitswitchingC.packetswitching D.messageswitching44.Whichcanchoosethebestroutethroughthenetwork?()A.networknodes B.packetsC.routepackets D.messages45.Packetswitching()A.canmakeabiggercostnetworkB.canmakealowercostnetworkC.canchoosefewerroutethroughthenetworkD.cannotemploystore-and-forwardprinciples46.Inthisarticle“ameshnetwork”means()A.aformofmeshsystemordeviceB.oneoftheopenspacesofthestrands(河岸,线束)ofanetC.somethingwhichcaptures(捕捉)andholdsfastD.atleasttworoutesbetweenanytwonodes47.Forthedurationofthecommunication,()A.alogicalpathshouldbesetup B.ameshnetworkshouldbesetupC.routepacketsshouldbesetup D.networknodesshouldbesetup48.DatagramroutingandVirtualcircuitroutingare()A.thesameroutingB.betterthanapacketswitchingC.twotypesofpacketswitchingroutingconceptsD.nottwoty