《计算机专业英语》Unit 12 Internet

Unit12InternetContentsLearningObjectives1Words&Expressions2Text3Exercises4Learning

ObjectivesAfteryouhavereadthisunit,youshouldbefamiliarwith:1.WhatisInternet?2.HowtoconnecttotheInternet?3.WhatisIPaddress?

Words&Expressionsapproximatelyadv.近似地，大约haphazarda.偶然的，随便的configurationn.构造,结构,配置,外形wirelessadj.无线的modulatorn.调制器demodulatorn.解调器conversationn.会话,交谈simultaneouslyadv.同时地digitaln.数字,数字式a.数字的,数位的,手指的cost-effectivea.有成本效益的，划算的ISPInternet服务提供者cellularphone便携式电话TextTheInternetisavastandsprawlingnetworkreachingintocomputersitesworldwide.Considerthatby1985,approximatelyonehundrednetworksformedtheInternet.By1989,thatnumberhadrisentofivehundred.Ifweextrapolateitbasedoncurrentnumbers,theInternetcouldreachfortymillionpeopleby1995,onehundredmillionby1998.Itscurrentgrowthrateis15percentmonthly.ConnectingtotheInternetInternetisadatacommunicationnetworkthatgrewovertimeinasomewhathaphazardconfigurationasnetworksconnectedtoothernetworks.Internetbackboneprovidesthemainhigh-speedroutesfordatatraffic.TheInternetbackboneconsistsofhigh-speedfiber-opticlinksconnectinghigh-capacityroutersthatdirectnetworktraffic.TextBackbonelinksandroutersaremaintainedbyInternetserviceproviders(ISP).ISPequipmentandlinksaretiedtogetherbynetworkaccesspoints.LargeISPsconnectdirectlytobackbonerouters;smallerISPstypicallyconnecttoalargerISPtogainInternetaccessandsupplyittotheircustomers.Universities,colleges,andmostlargebusinesshavededicatedhigh-speedcablethatprovidesadirectconnectiontotheInternet.OneofthemostchallengingaspectsoftheInternetisselectingaconnection.Althoughmostpeoplebeginwithadial-upconnection,manysoonexplorehigh-speedInternetaccessoptions.Interestisalsogrowinginusinghome-basedLANandwirelessInternetaccess.Generally,userscangetaccesstoInternetbyseveralapproachessuchasdial-upconnections,DLS,ISDN,orLANInternetaccess.Dial-upConnectionAdial-upconnectionusesPOTS(plainoldtelephoneservice)totransportdatabetweenyourcomputerandyourISP.Sincethetelephonenetworkfunctionsbyconvertingsoundintoelectronicsignals,thecomputermustfirstconvertitsdigitaldataintosound.Adevicecalledmodem,whichisshortformodulator/demodulator,playstheroleofsignalconverting.Amodemconvertsthedigitalsignalfromacomputerintoananalogsignalthatcanbetransmittedoverthetelephonenetwork.Themodemofreceivingcomputerdemodulatestheanalogsoundsignalbackintoadigitalformthatthecomputercanunderstand.Whenyouuseadial-upconnection,yourcomputer'smodemessentiallyplacesaregulartelephonecalltoyourISP.Yourcallisroutedthroughthetelephonecompany'slocalswitchandouttotheISP.WhentheISP'scomputer"answers"yourcall,adedicatedcircuitisestablishedbetweenyouandyourISP.ThecircuitremainsconnectedforthedurationofyourcallandprovidesacommunicationslinkthatcarriesdatabetweenyourcomputerandISP.AsyourdataarrivesattheISP,aroutersendsitoutovertheInternet.Dial-upconnectioncan'tprovideafastdatatransmission.Ifyouhaveonlyonetelephoneline,youcannotpickupyourtelephonereceiver,dialyourfriend,andcarryonavoiceconversationwhileyouaresendingdata.High-speedInternetAccess—DSLandISDNConnectionDSLandISDNareotheroptionsavailableforhigh-speedInternetaccess,byusingtelephonenetwork.DSL(digitalsubscriberline)isahigh-speed,digital,always-on,Internetaccesstechnologythatrunsoverstandardphonelines.ItisoneofthefastestInternetconnectionsthatareaffordabletoindividualconsumers.Severalvariationsofthistechnologyexits,includingASDL(asymmetricDSL,withdownstreamspeedfasterthanupstreamspeed),SDSL(symmetricDSL,withthesameupstreamanddownstreamspeed),andHDSL(high-rateDSL).DSLisdigital,sodatadoesn’tneedtobechangedintoanalogformandthenbacktodigitalasitdoeswhenyouuseadial-upconnection.ADSLconnectioncansimultaneouslycarryvoiceanddata,ifpermittedbyyourDSLprovider.ThedigitaldataandanalogvoicesignalstravelovertheDSLlinetothelocalswitchingstation.TherethevoicesignalsareinterpretedbyspecialequipmentcalledaDSLAM(DSLAccessMultiplexer)androutedoverhigh-speedlinestoaDSLproviderordirectlytotheInternet.ThespeedofaDSLconnectionvariesaccordingtothecharacteristicsofyourtelephoneline,theequipmentatyourlocalswitch,andyourdistancefromtheswitchingstation.MostDSLmodemsareratedfor1.5Mbpsdownstream.ISDN(IntegratedServiceDigitalNetwork)connectionsmovedataatspeedsof65Kbpsor128Kbps,whichisnotasfastasDSLbutfasterthanadial-upconnection.ISDNisanall-digitalservicewiththepotentialtosimultaneouslycarryvoiceanddata.AdevicecalledanISDNterminaladapterconnectsacomputertoatelephonewalljack,andtranslatesthecomputer'sdigitalsignalsintoadifferentkindofdigitalsignalthatcantravelovertheISDNconnection.LANInternetAccessALANprovidesacost-effectivewaytoshareoneInternetconnectionamongseveralcomputers.SchoolcomputerlabsandbusinessesusuallyprovideInternetaccessviaLAN.LANInternetaccessisalsofeasibleforhomenetworks.AsingleDSL,ISDN,orsatelliteconnectioncanbecabledintoyourhomeLANandaccessedbyallcomputers.ToestablishLANInternetaccess,severalcomponentsareneeded:(1)anoperationalwiredorwirelessLAN;(2)arouterorahubwithroutercapabilities;(3)ahigh-speedInternetconnection,suchasDSL,ISDN;(4)amodemthatcorrespondstoyourInternetconnectiontype.Asinformationtechnologydevelops,youcanuseamobileInternetconnectiontosurftheWebandcheckyoure-mail.Currently,devicessuchascellphones,PDAs,notebookcomputers,andtabletcomputerscanbeeasilyconfiguredformobileInternetaccess.ThecellularphoneserviceisoneofthemostpopularoptionsformobileInternetaccess.IfyouwanttoaccessInternetfromthecellularphone,youcansubscribetoaWAPplanofferedbyyourcellularphoneprovider.WAP(WirelessAccessProtocol)isacommunicationprotocolthatprovidesInternetaccessfromhandhelddevices,suchascellphonesandPDA.WAP-enableddevicescontainamicrobrowserthatsimplifiesWebande-mailaccessonasmall,low-resolutionscreen.InternetAddressingAsweknow,TCP/IPprovidesastandardforInternetdatacommunication.TCPbreaksamessageorafileintopackets,andIPisresponsibleforaddressingpacketssothattheycanberoutedtotheirdestination.Howthepacketscanpreciselyreachthetargetmachine?TobepartoftheInternet,acomputermusthaveauniqueIPnetworkaddressforcorrectlyroutingtoandfromthemachineoverInternet.AnIPaddressisaseriesofnumber,suchas.AnIPaddressisseparatedintofoursectionsbyperiodsforconvenienceofhumanreaders.Thenumberinasectioncannotexceed255.Inbinaryrepresentation,eachsectionofanIPaddressrequires8bits,sotheentireaddressrequires32bits.InternetaddressesarecalledURLs(UniformResourceLocators).BecausethelongstreamofnumberofURLisdifficultforpeopletoremember,manyInternetserversalsohaveaneasy-to-remembername,suchas.Theofficialtermforthisnameis“fullyqualifieddomainname”(FQDN),butmostpeoplejustrefertoitasadomainname.AdomainnameisakeycomponentofURLsande-mailservernameinane-mailaddress.Forexample,intheURL,thedomainnameis.Intheemailaddressjassica@,thedomainnameisalso.Adomainnameendswithanextensionthatindicatesitstop-leveldomain.Domainnamescantellyouagreatdealaboutwhereacomputerislocated.ForcomputerslocatedintheUnitedStates,tope-leveldomainnamesindicatethetypeoforganizationinwhichthecomputerislocated.Someofthemostcommonlyusedtop-leveldomainsarecom(commercialbusiness),edu(educationinstitutions),net(networkorganizations),gov(governmentagencies),andorg(nonprofitorganization).OutsidetheUnitedStates,countrycodesalsoserveastop-leveldomainssuchasca(Canada),uk(UnitedKingdom),cn(China).SincethepacketscanonlyidentifynumericIPaddress,theDomainNameSystem(DNS)isrequiredtorecordeverydomainnamethatcorrespondstoauniqueIPaddress.AdomainnamemustbeconvertedintoanIPaddressbeforeanypacketscanberoutedtoit.TheDNSisbasedonadistributeddatabase.Surprisingly,thisisnotstoredasawholeinasinglelocation;instead,itexistsinpartsallovertheInternet.YourInternetconnectionissetuptoaccessoneofthemanydomainnameserversthatresideontheInternet.Exercises1.Answerthefollowingquestionaccordingtothetext.(1)WhatisInternet?(2)HowmanymethodstoconnecttotheInternet?(3)WhatisanIPaddress?(4)Whatconstitutesadomainname?2.TranslatethefollowingtermsorphrasesfromEnglishintoChineseandviceversa:(1)LAN(6)调制器(2)ISP(7)解调器(3)ISDN(8)统一资源定位器(4)DSL(9)域名系统(5)WAP(10)掌上电脑key3.Fillintheblankswiththeinformationgiveninthetext:

(1) Internet

providesthemainhigh-speedroutesfordatatraffic.(2) Generally,userscangetaccesstoInternetbyseveralapproachessuchas

,

,

,or

.(3)

isoneofthemostpopularoptionsformobileInternetaccess.(4) AnIPaddressisseparatedinto

sectionsbyperiodsforconvenienceofhumanreaders.Thenumberinasectioncannotexceed

.(5) Someofthemostcommonlyusedtop-leveldomainsare

,

,

,

,and

.key4.Choosethebestonefromtheitemsgivenbelowtocompletethefollowingpassage.TraditionalInternetaccessmethodslikedial-upweresoslowthathostcomputerswereconnectedtothedial-up(1)atthecustomerpremiseoverslow(2)ports.PPPwasdesignedtorundirectlyovertheseseriallinks.ButwiththeadventofbroadbandInternet(3)technologiessuchasADSLandcablemodemstherehasbeenaconsiderableincreaseinthebandwidthdeliveredtotheendusers.Thismeansthatthehostcomputersatthecustomerpremiseconnecttothe(4)orcable“modem”overamuchfastermediumsuchasEthernet.Italsomeansthatmultiple(5)canconnecttotheInternetthroughthesameconnection.(1)A.buffer B.modem C.computer D.server(2)A.parallel B.digital C.serial D.variable(3)A.access B.cache C.cost D.storage(4)A.FDDI B.HDSL C.ADSL D.CDMA(5)A.cables B.hosts C.servers D.modemskey5.MarkthefollowingstatementswithT(true)orF(false)accordingtothetext.(1)Internetisadatacommunicationnetworkthatgrewovertimeinasomewhathaphazardconfigurationasnetworksconnectedtoothernetworks.(2)Sincethetelephonenetworkfunctionsbyconvertingelectronicsignalsintosound,thecomputermustfirstconvertitsdigitaldataintosound.(3)Amodemconvertsthedigitalsignalfromacomputerintoananalogsignalthatcanbetransmittedoverthetelephonenetwork.(4)ADSLisahigh-speed,digital,always-on,Internetaccesstechnologythatrunsoverstandardphonelines.ItisoneofthefastestInternetconnectionsthatareaffordabletoindividualconsumers.(5)Inbinaryrepresentation,eachsectionofanIPaddressrequires6bits,sotheentireaddressrequires32bits.key6.Selecttheoneanswertoeachquestion.(1)The“WWW”isexactlywhat?A.AwebofresourcesontheInternetthatareaccessedB.TheInternetusingHTTPC.AnISPorInternetServiceProviderD.InternetExplorer(2)A(n)

isanintricatelyconnectedsystemofobjectsorpeople.A.operatingsystem B.computersystem C.network D.LAN(3)ThestandardprotocolfortheInternetis.A.TCP/IP B.NOSC. DSL D.OSI(4)Innetworking,a(n)

isamaterialthroughwhichdatapacketstravel.A.router B.repeater C.E-Mail D.medium(5)

describeshowthenetworkisarranged.A.DSL B.NodeC. NOS D.Topology

(6)An

convertsdatafrompulseformtowaveformandbackagain。A．modemB．channelC．controlunitD．interfacekey7.TranslatethefollowingsentencesintoChinese.(1)Ifweextrapolateitbasedoncurrentnumbers,theInternetco