计算机专业英语第二章第二节幻灯.ppt

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1、Section 2 Data Communications Channels1.1课前导读1.2课堂教学1.2.1NewWords1.2.2Phrases1.2.3Abbreviations1.2.4Text1.3Exercises1.1课前导读Togetheretothere,datamustmovethroughsomething.Atelephoneline,cable,ortheatmospherearealltransmissionmedia,orchannels.Butbeforethedatacanbecommunicated,itmustbeconvertedintoaform

2、suitableforcommunication.Specifically,fivekindsoftechnologyareusedtotransmitdata.Thesearetelephonelines(twistedpair),coaxialcable,fiber-opticcable,microwave,andsatellite.1.2 课堂教学课堂教学 1.2.1 New Wordsantennan.天线axisn.轴心,中轴basebandn.基带Boostv.增加，放大cablen.电缆charge n.电荷claddingn.金属包层,外罩coaxialadj.同轴的,共轴的C

3、onfigurationn.配置，结构，布局，格局curvaturen.弯曲，曲度，弧度Electromagneticadj.电磁的fiber-opticn.光纤garble v.精选,筛去的杂质,误解gauge n.规格，标准geostationary adj.与地球相对位置保持不动的interferencen.干扰，串扰，干涉immuneadj.免疫的multidropn.多点outcomen.结果，产量，出口phase v.逐步采用polen.极(点)；杆；电极pulsen.脉冲relayv.中继，转播sheath n.外皮，外层复盖物shield n.屏,保护;防护，屏蔽strand

4、n.绳股，绞合线susceptibleadj.灵敏的（敏感的）twistedn.扭绞的utilizationn.应用，利用woven adj.纺织的，编织的1.2.2 Phrasescoaxialcable同轴电缆fiber-opticcable光缆geostationaryorbitingsatellite轨道通信卫星multiple-conductor多重导体phaseout（逐步）取消twistedpair双绞线wovenwire钢丝网，铁丝网1.2.3 AbbreviationsLED（Light-EmittingDiode）发光二极管1.2.4 TextTogetheretother

5、e,datamustmovethroughsomething.Atelephoneline,cable,ortheatmospherearealltransmissionmedia,orchannels.Butbeforethedatacanbecommunicated,itmustbeconvertedintoaformsuitableforcommunication.Datacommunicationslinescanbeconnectedintwotypesofconfigurations:point-to-point and multidrop.A point-to-pointline

6、directlyconnectsthesendingandthereceivingdevices,andamultidroplineconnectsmanydevices,notjustonesendingdeviceandonereceivingdevice.The two ways of connecting microcomputers with each otherandwithotherequipmentsarethroughthecableandthroughtheair.Therearethreebasicformsintowhichdatacanbeconvertedforco

7、mmunication:electricalpulsesorcharges,electromagneticwaves,andpulsesoflight.Specifically,fivekindsoftechnologyareusedtotransmitdata.These are telephone lines(twisted pair),coaxial cable,fiber-opticcable,microwave,andsatellite.TelephoneLines1Inexpensive,multiple-conductorcablecomprisedofoneormorepair

8、sof18to24gaugecopperstrands.Thestrandsaretwisted to improve protection against electromagnetic and radiofrequencyinterference.Thecable,whichmaybeeithershieldedor unshielded,is used in low-speed communications,as telephonecable.It is used only in baseband networks because of its narrowbandwidth.Mostt

9、elephonelinesyouseestrungonpolesconsistofcablesmadeupofhundredsofcopperwiresaretwistedpairs.Twistedpairs are susceptible to a variety of types of electrical interference(noise),whichlimitsthepracticaldistancethatdatacanbetransmittedwithoutbeinggarbled.Twistedpairshavebeenusedforyearsforvoiceanddatat

10、ransmission,howevertheyarenowbeingphasedoutbymoretechnicallyadvancedandreliablemedia.CoaxialCableCoaxialcableisatypeofthicklyinsulatedcopperwirethatcancarryalargervolumeofdataabout100millionbitspersecond,theinsulationiscomposedofanonconductivematerialcoveredbyalayerofwovenwiremeshandheavy-dutyrubber

11、orplastic.Intermsofnumberoftelephoneconnections,a coaxial cable has 80 times the transmissioncapacityoftwistedpair.Coaxialcablesaremostoftenusedastheprimarycommunicationsmediumforlocalconnectednetworkinwhichallcomputercommunicationiswithinalimitedgeographicarea,suchasinthesamebuilding.Coaxialcableis

12、alsousedforunderseatelephonelines.Fiber-OpticCable 2Atransmissionmediumcomposedofacentralglassopticalfibercablesurroundedbycladdingandanouterprotectivesheath.IttransmitsdigitalsignalsintheformofmodulatedlightfromalaserorLED(light-emittingdiode).Infiber-opticcable,dataistransmitted as pulses of light

13、 through tubes of glass.In terms ofnumberoftelephoneconnections,fiber-opticcablehas20,000timesthetransmissioncapacityoftwistedpair.However,itissignificantlysmaller.Indeed,afiber-optictubecanbehalfthediameterofahumanhair.Althoughlimitedinthedistancetheycancarryinformation,fiber-optic cables have seve

14、ral advantages.Such cables are immune toelectronicinterference,whichmakesthemmoresecure.Theyarealsolighterandlessexpensivethancoaxialcableandaremorereliableattransmittingdata.Theytransmitinformationusingbeamsoflightatlightspeedsinsteadofpulsesofelectricity,makingthemfarfasterthancopper cable.Fiber-o

15、ptic cable is rapidly replacing twisted-pairtelephonelines.MicrowaveInsteadofusingwireorcables,microwavesystemscanusetheatmosphereasthemediumthroughwhichtotransmitsignals.Microwavesarehigh-frequencyradiowavesthattravelinstraightlinesthroughtheair.Becausethewavescannotbendwiththecurvatureoftheearth,t

16、heycanbetransmittedonlyovershortdistances.Thus,microwave is a good medium for sending databetweenbuildingsinacityoronalargecollegecampus.Forlongerdistances,the waves must be relayed by means of dishes,orantennas.These can be installed on towers,high buildings,andmountaintops.Eachtowerfacilityreceive

17、sincomingtraffic,booststhesignalstrength,andsendsthesignaltothenextstation.Satellites3Satellitecommunicationsreferstotheutilizationofgeostationaryorbitingsatellitestorelaythetransmissionreceivedfromoneearthstationtooneormoreearthstations.Theyaretheoutcomeofresearchintheareaofcommunicationswhoseobjec

18、tiveistoachieveever-increasingrangesandcapacitieswiththelowestpossiblecosts.Orbitingabout22,000milesabovetheearth,satellitesrotateataprecisepointandspeedabovetheearth.Thismakesthemappearstationarysotheycanamplifyandrelaymicrowavesignalsfromonetransmitteronthegroundtoanother.Theprimaryadvantageofsate

19、llitecommunicationistheamountofareathatcanbecoveredbyasinglesatellite.Italsohasotherfeatures:longcommunicationdistance,andthe cost of station building is independent of thecommunicationdistance,operatinginbroadcastingmode,easyformultipleaccess,sustainingheavytraffic,abletotransportdifferenttypesofse

20、rvice,independentsendingandreceiving,andmonitoring.Threesatellitesplacedinparticularorbitscancovertheentiresurfaceoftheearth,withsomeoverlap.Theironlydrawbackisthatbadweathercansometimesinterrupttheflowofdata.1.3Exercises.Writetrueorfalseforthefollowingstatementsaccordingtothepassage.1.()Aircanbeuse

21、dtotransmitdata.2.()Point-to-poing and multidrop are two types ofconfigurationforcommunicationslinesconnecting.3.()Twistedpairsaresusceptibletonoise,whichlimitsthepracticaldistancetheycantransmit.4.()Coaxicalcableandtwistedpairsareallhigh-frequencytransmissioncables.5.()Optic-fibercablescantransmitb

22、othelectricalandlightsignals.6.()Optic-fibercablesaremoresecurebecausetheyarenotsusceptibletoelectricalinterference.7.()Microwavecantransmitdataoverlongdistances.8.()Theprimaryadvantageofsatellitecommunicationisthelongdistanceasinglesatellitecancover.9.()Threesatellitesplacedinrandomorbitscancoverth

23、eentiresurfaceoftheearth.10.()Ofallthefivekindsofcommunicationschannels,becausetheyallhavetheirownadvantagesanddisadvantages,sotheycannotreplacewitheachother.Fillintheblanksaccordingtothepassage.1.Thetwowaysofconnectingmicrocomputerswitheachotherandwithotherequipmentsarethroughthe_andthroughthe_.2.D

24、atacommunicationslinescanbeconnectedintwotypesofconfigurations:_and_.3.Twisted pairs are _ to a variety of types ofelectricalinterference(noise),whichlimitsthepracticaldistancethatdatacanbetransmittedwithoutbeing_4._transmitsdigitalsignalsintheformofmodulatedlightfromalaserorLED5._systemscanusetheat

25、mosphereasthemediumthroughwhichtotransmitsignals.6.Microwaves cannotbendwiththe_ of theearth,theycanbetransmittedonlyovershortdistances.7.Satellitecommunicationsreferstothe_ofgeostationary orbiting satellites to _the transmissionreceivedfromoneearthstationtooneormoreearthstations.8.Threesatellitespl

26、acedinparticularorbitscancovertheentiresurfaceoftheearth,withsome_.9.Fiber-opticcablesare_toelectronicinterference,whichmakesthemmoresecure.10.In order to transmit longer distance,microwave must berelayedbymeansof_.TranslatethefollowingwordsandexpressionsintoCmunicationschannels 6.electromagneticwaves2.multiple-conductor7.pulsesoflight3.facility8.light-emittingdiode4.stationary9.asolidwireconductor5.transmissioncapacity10.electricalinterference