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1、畢業(yè)設(shè)計（外文翻譯材料）TelecommunicationModernOperationTelephoneInananaloguetelephonenetwork,thecallerisconnectedtothepersonhewantstotalktobyswitchesatvarioustelephoneexchanges.Theswitchesformanelectricalconnectionbetweenthetwousersandthesettingoftheseswitchesisdeterminedelectroni
2、callywhenthecallerdialsthenumber.Oncetheconnectionismade,thecaller'svoiceistransformedtoanelectricalsignalusingasmallmicrophoneinthecaller'shandset.Thiselectricalsignalisthensentthroughthenetworktotheuserattheotherendwhereittransformedbackintosoundbyasmallspeakerinthatp
3、erson'shandset.Thereisaseparateelectricalconnectionthatworksinreverse,allowingtheuserstoconverse.Thefixed-linetelephonesinmostresidentialhomesareanalogue—thatis,thespeaker'svoicedirectlydeterminesthesignal'svoltage.Althoughshort-distancecallsmaybehandledfromend-to-endas
4、analoguesignals,increasinglytelephoneserviceprovidersaretransparentlyconvertingthesignalstodigitalfortransmissionbeforeconvertingthembacktoanalogueforreception.Theadvantageofthisisthatdigitizedvoicedatacantravelside-by-sidewithdatafromtheInternetandcanbeperfectlyreprodu
5、cedinlongdistancecommunication(asopposedtoanaloguesignalsthatareinevitablyimpactedbynoise).Mobilephoneshavehadasignificantimpactontelephonenetworks.Mobilephonesubscriptionsnowoutnumberfixed-linesubscriptionsinmanymarkets.Salesofmobilephonesin2005totalled816.6millionwith
6、thatfigurebeingalmostequallysharedamongstthemarketsofAsia/Pacific(204m),WesternEurope(164m),CEMEA(CentralEurope,theMiddleEastandAfrica)(153.5m),NorthAmerica(148m)andLatinAmerica(102m).Intermsofnewsubscriptionsoverthefiveyearsfrom1999,Africahasoutpacedothermarketswith58.
7、2%growth.Increasinglythese-6--phonesarebeingservicedbysystemswherethevoicecontentistransmitteddigitallysuchasGSMorW-CDMAwithmanymarketschoosingtodepreciateanaloguesystemssuchasAMPS.Therehavealsobeendramaticchangesintelephonecommunicationbehindthescenes.Startingwiththeop
8、erationofTAT-8in1988,the1990ssawthewidespreadadoptionofsystemsbasedonopticfibres.Thebenefitofcommunicatingwith
