Unit10TelecommunicationNetworks10.1ATelephoneNetwork

10.2InternetTelephony10.1AtelephonenetworkWordsandExpressionsBackgroundsTextWordsandExpressionstelephoneexchange電話局；總機(jī)；電話交換機(jī)；電信交換ubiquitous adj.無處不在的；十分普遍的Sincethen(AlexanderGrahamBellinventedthetelephonein1876,andtheworld’sfirsttelephoneexchangewasopenedin1878),telephonyhasbecometheubiquitousmeansofcommunicatingformankind.從那時(shí)起，電話已經(jīng)成為人類無處不在的通信手段。WordsandExpressions5vocaltract 聲道Duringtalking,variationsinairpressurearegeneratedbythevocaltractofthespeaker.touch-tonekeypad 按鍵式鍵盤Atouch-tonephonekeypadproducesaDTMFsignalingtoneconsistingoftwosimultaneouspuretonesinusoidalfrequencieswhenakeyispressed.WordsandExpressions6scalingproblem 縮放問題；尺度問題call-controlsoftware 呼叫控制軟件Today,telephoneexchangesarefullyautomatic,theexchangecontrolisprovidedbycomputerswiththeprocedurescapturedincall-controlsoftware.automanualexchange

半自動交換臺；自動手動切換whenahumaninterventionisrequired,forexample,providingvariousformsofassistanceandemergencycallsWordsandExpressions7PSTN:PublicSwitchedTelephoneNetwork公用電話交換網(wǎng)POTS:PlainOldTelephoneService 普通傳統(tǒng)電話業(yè)務(wù)dialtone

撥號音ThedialtoneisgeneratedbythePSTNexchangetoindicatetothephoneuserthattheexchangewasreadytoacceptthenumber.SLIC:SubscriberLineInterfaceCircuit

用戶線接口電路；用戶接口電路WordsandExpressions8BORSCHT:Batteryfeed 饋電Overvoltageprotection

過壓保護(hù)Ringing 振鈴Supervision 監(jiān)視Codec:codinganddecoding

編解碼Hybrid

混合（用戶線2/4線轉(zhuǎn)換）Test

測試WordsandExpressions9Vrms:root-mean-squarevoltage電壓均方根值；電壓有效值trunkline

干線subscriberbranchline

用戶分線tolloffice 長途局；長途電話局；長途端局；收費(fèi)站exchangenumber 交換局號areacode 區(qū)號LEC:LocalExchangeCarrier 本地交換運(yùn)營商/公司W(wǎng)ordsandExpressions10LATA:LocalAccessandTransportAreas本地接入和傳輸區(qū)域IXC:IntereXchangeCarrier 局間通信公司；長途電話公司POP:PointofPresence 入網(wǎng)點(diǎn)；出現(xiàn)點(diǎn)；存在點(diǎn)hierarchical adj.等級制的；按等級劃分的Mostlong-distancecarriershavetheirownspecifichierarchicalarrangements.Avarietyofswitchingofficesacrossthecountryarelinkedbytrunksusingfiber-opticcableormicrowaverelaylinks.WordsandExpressions11call-forwarding 呼叫轉(zhuǎn)移numberdisplay 來電顯示three-waycalling 三方通話；三方通信；電話會議signalingsystem 信令系統(tǒng)SignalingSystem7(SS7)isanarchitectureforperformingout-of-bandsignalinginsupportofthecall-establishment,billing,routing,andinformation-exchangefunctionsofthePSTN.Background12LearnBasicsofTelecommunicationNetworks，/course/telecom-network-architecture/TextOutline13IntroductionBasicTelephonyTelephoneSystemIntroduction14Ofcourse,telecommunicationsarenowglobalandincludenotonlytelephonyoverfixedandmobilenetworks,butalsodata–theWorldWideWeb,e-mail,broadcastTV,video,socialnetworking,etc.Introduction15Insettingouthowallofthisworks,

itishelpfultounderstandhowthebasictelephonenetworksarestructuredsincetheyformthebasisofalltoday’stelecommunicationsnetworks.在闡述所有這些工作原理時(shí)，了解基本電話網(wǎng)絡(luò)的結(jié)構(gòu)是有幫助的，因?yàn)樗鼈儤?gòu)成了當(dāng)今所有電信網(wǎng)絡(luò)的基礎(chǔ)。BasicTelephony16Soundwaves,travelfromthespeakertothemicrophone,whichconvertsthemintoanelectricalsignalvaryinginsympathywiththepatternofthesoundwaves.BasicTelephony17Atthereceivingendofthecircuittheanalogueelectricalsignalenergizesthereceiver(i.e.anearpiece),generatingasetofsoundwaves,whichareanapproximatereproductionofthesoundofthespeaker.在電路的接收端，模擬電信號為激勵接收器（即聽筒），產(chǎn)生一組聲波，它們是說話者聲音的近似再現(xiàn)。BasicTelephony18Thesolutiontothescalingproblemistointroduceacentralhub(commonlycalledanexchangeorcentraloffice)Figure10.2Directinterconnectionofseveralphones.Forfourphones,numberoflinksrequired=6Generally:Fornphones,numberoflinksrequired=n(n–1)/2Figure10.3Interconnection:Useofanexchange.Fornphones,numberoflinkstoeachexchange=nTelephoneSystem19Thetelephonesystemiscalledthepublicswitchedtelephonenetwork(PSTN).Youwillsometimeshearthetelephonesystemreferredtoastheplainoldtelephoneservice(POTS).SubscriberInterfaceTelephoneHierarchyTelephoneSystem20Mosttelephonesareconnectedtoalocalcentralofficebywayofthetwo-line,twisted-pairlocalloopcable.Eachtelephoneconnectedtothecentralofficeisprovidedwithagroupofbasiccircuitsthatpowerthetelephoneandprovideallthebasicfunctions,suchasringing,dialtone,anddialingsupervision.Thesecircuitsarecollectivelyreferredtoasthesubscriberinterfaceorthesubscriberlineinterfacecircuit(SLIC).TelephoneSystem21TheSLICprovidessevenbasicfunctionsgenerallyreferredtoasBORSCHT.TelephoneSystem22BatteryFeed.ThesubscriberlineinterfaceatthecentralofficemustprovideaDCvoltagetothesubscribertooperatethetelephone.on-hook掛機(jī)off-hook摘機(jī)TelephoneSystem23OvervoltageProtection.Thecircuitsandcomponentsthatprotectthesubscriberlineinterfacecircuitsfromelectricaldamage.LightningMisconnectionNoiseTelephoneSystem24Ringing.Whenaspecifictelephoneisreceivingacall,thetelephonelocalofficemustprovidearingingsignalthatiscommonlya90-VrmsACsignalatapproximately20Hz.Supervision.Supervisionreferstoagroupoffunctionswithinthesubscriberlineinterfacethatmonitorlocalloopconditionsandprovidevariousservices.TelephoneSystem25Codec.CodingisanothernameforA/DconversionandD/Aconversion.Transmissionovertrunklinestoothercentralofficesortollofficesorforuseinlong-distancetransmissionistypicallybydigitalPCMsignalsinmodernsystems.在現(xiàn)代系統(tǒng)中，（語音信號）通過干線傳輸?shù)狡渌娫挾司只蜷L途電話局，或用于遠(yuǎn)距離傳輸，通常采用數(shù)字PCM信號。TelephoneSystem26Hybrid.Ahybridcircuit(alsoknownasatwo-wiretofour-wirecircuit),usuallyatransformer,providessimultaneoustwo-wayconversationsonasinglepairofwires.Ahybridisalsousedatthecentraloffice.Iteffectivelytranslatesthetwo-wirelinetothesubscriberbackintofourlines,twoeachforthetransmittedandreceivedsignals.TelephoneSystem27Test.Tocheckthestatusandqualityofsubscriberlines,thephonecompanyoftenputsspecialtesttonesonthelocalloopandreceivesresultingtonesinreturn.TheSLICprovidesawaytoconnectthetestsignalstothelocalloopandtoreceivetheresultingsignalsformeasurement.TelephoneSystem28HierarchicalOrganizationofTelephoneSystemTelephoneSystem29Alsoknownasanendoffice(EO),thelocalexchangecanserveupto10,000subscribers,eachofwhomisidentifiedbyafour-digitnumberfrom0000through9999(thelastfourdigitsofthetelephonenumber).本地交換局，也稱為終端局（EO），可為多達(dá)10000個(gè)用戶提供服務(wù)，每個(gè)用戶由0000到9999（電話號碼的最后四位）之間的一個(gè)4位數(shù)字進(jìn)行標(biāo)識。TelephoneSystem30Thelocalexchangealsohasanexchangenumber.Theseexchangesbecomepartofaregion,whichisdefinedbyanareacode.Eachareacodeisfullycontainedwithinoneofthegeographicareasassignedtooneoftheregionaloperatingcompanies.Thesecompaniesarecalledlocalexchangecarriers,orlocalexchangecompanies(LECs).TelephoneSystem31TheLECsprovidetelephoneservicestodesignatedgeographicareasreferredtoaslocalaccessandtransportareas(LATAs).Long-distanceserviceisprovidedbylong-distancecarriersknownasinterexchangecarriers(IXCs).Mostlong-distancecarriershavetheirownspecifichierarchicalarrangements.TelephoneSystem32Signaling

usesdigitalpacketstoperformallofthevariousoperationsnecessarytoestablishaconnectionandtearitdown.Typicalfunctionsincludebilling,callmanagement(suchascall-forwarding,numberdisplay,three-waycalling,and800and900calls),androutingofcallsfromonepointtoanother.10.2InternetTelephonyWordsandExpressionsBackgroundsText33WordsandExpressionsInternettelephony/IPtelephony/VoIP網(wǎng)絡(luò)電話；互聯(lián)網(wǎng)電話VoIP

isahighlycomplexdigitalvoicesystemthatreliesonhigh-speedInternetconnectionsfromcableTVcompanies,phonecompaniessupplyingDSL,andotherbroadbandsystemsincludingwireless.VoIP是一種高度復(fù)雜的數(shù)字語音系統(tǒng)，依賴于來自有線電視公司，提供DSL的電話公司以及其他寬帶系統(tǒng)（包括無線）的高速互聯(lián)網(wǎng)連接。WordsandExpressions35bypass vt.繞過；避開bypasscircuit 旁路電路bypassswitch/diode/capacitor/line/controlITU:InternationalTelecommunicationsUnion 國際電信聯(lián)盟algorithm n.算法；計(jì)算程序Variousmathematicalalgorithmsbeyondthescopeofthistextareused.使用了本文范圍之外的各種數(shù)學(xué)算法。WordsandExpressions36designate vt.命名；指定；選定；標(biāo)明；指明The64-kbpsdigitalsignalisdesignatedasstandardG.711andisbetterknownaspulse-codemodulation(PCM),coveredearlierinthisbook.64kbps數(shù)字信號被指定為標(biāo)準(zhǔn)G.711，更廣為人知的是脈沖編碼調(diào)制（PCM），在本書前面已經(jīng)介紹過。WordsandExpressions37echocancellation 回聲消除；回波消除echocancellationaimstofiltertheechothatiseitherproducedbyacousticmeansorahybridechoproducedbylineecho,electricalreflectionsorimpedancemismatch.WordsandExpressions38extract v.提??；摘錄；提煉；獲得 n.提取物；摘錄；節(jié)錄decompress v.解壓縮（將壓縮文件等恢復(fù)到原大小）Fromthere,thecompresseddataisextracted,decompressedbyaDSP,andsenttotheDACinthecodecwheretheoriginalvoiceisheard.從那里，壓縮數(shù)據(jù)被提取，由DSP解壓縮，并發(fā)送到編解碼器中的DAC，在那里聽到原始語音。WordsandExpressions39outofsequence 失序；順序混亂地；次序錯(cuò)誤insequence 依次，順次outoforder/inorder,outofturn/inturnIETF:InternetEngineeringTaskForce互聯(lián)網(wǎng)工程任務(wù)組SIP:SessionInitiationProtocol 會話初始化協(xié)議ATA:AnalogTerminalAdapter 模擬終端適配器cordlessphone 無線電話；無繩電話機(jī)；室內(nèi)無線電話Background40VoIPDesignandTelephonyFundamentals,/course/voip-design-and-telephony-fundamentals/TextOutline41IntroductionVoIPFundamentalsInternetPhoneSystemsIntroduction42Internettelephony,alsocalledInternetProtocol(IP)telephonyorvoiceoverInternetprotocol(VoIP),usestheInternettocarrydigitalvoicetelephonecallswithoutphonecompanycharges.互聯(lián)網(wǎng)電話，也稱為互聯(lián)網(wǎng)協(xié)議（IP）電話或互聯(lián)網(wǎng)協(xié)議語音（VoIP），使用互聯(lián)網(wǎng)承載數(shù)字語音電話呼叫，而無需交電話費(fèi)。Introduction43WhilethelegacyPSTNwillvirtuallynevergoaway,overtimeitwillplayasmallerandsmallerroleasVoIPismorewidelyadoptedorasmoreandmoreindividualschooseacellphoneastheirmaintelephoneservice.雖然傳統(tǒng)的PSTN幾乎永遠(yuǎn)不會消失，但隨著時(shí)間的推移，隨著VoIP被更廣泛地采用或越來越多的人選擇手機(jī)作為他們的主要電話服務(wù)，PSTN將發(fā)揮越來越小的作用。VoIPFundamentals44SignalflowinaVoIPsystemCODECDSPVoIPprotocolprocessorEthernetInternetVoIPFundamentals45TheADCusuallysamplesthevoicesignalat8kHzandproducesan8-bitwordforeachsample.Thesesamplesoccuroneafteranotherseriallyandthereforeproducea64-kbpsdigitalsignal.StandardG.729aisprobablythemostcommoncompressionstandardusedandresultsinan8-kbpsdigitalvoicesignal.AnotherpopularstandardisG.723,whichproducesanevenmorehighlycompressed5.3-kbpssignalattheexpenseofsomevoicequality.VoIPFundamentals46MostVoIPphonescontainallthecommoncompressionstandardalgorithmsintheDSPmemoryforuseascalledfor.大多數(shù)VoIP電話在DSP內(nèi)存中包含所有常見的壓縮標(biāo)準(zhǔn)算法，以便按需使用。VoIPFundamentals47OneofthemainproblemswithVoIPisthatittakesarelativelylongtime:

packetstakedifferentroutes,causingoutofsequenceproblem

interveningroutersandserverseachaddslatencyIthasbeendeterminedthatthemaximumacceptablelatencyisabout150ms.VoIPFundamentals48InthePSTN,thedialingprocessinitiatesmultiplelevelsofswitchingthatliterallyconnectsthecallingphonetothecalledphone.InInternettelephony,nosuchtemporarydedicatedlinkisestablishedbecauseofthepacketizednatureofthesystem.在互聯(lián)網(wǎng)電話中，由于系統(tǒng)的分組交換本質(zhì)，主被叫之前并沒有建立這樣的臨時(shí)專用鏈路。VoIPFundamentals49TheinitialprotocolusedwastheITUH.323.Today,however,anewerprotocolestablishedbytheInternetEngineeringTaskForce(IETF)calledthesessioninitiationprotocol(SIP)hasbeenadoptedasthedefactostandard.然而，今天，因特網(wǎng)工程任務(wù)組（IETF）建立的一個(gè)新協(xié)議，稱為會話起始協(xié)議（SIP），已被采納為事實(shí)上的標(biāo)準(zhǔn)。InternetPhoneSystems50HomeVoIP.AnalogTerminalAdapter(ATA)connectsthestandardhometelephonetotheexistingbroadbandInternetmodem.AnotherconfigurationisaVoIPgatewaythatcontainstheATAcircuitryaswellasthebroadbandmodem.InternetPhoneSystems51HomeVoIPRJ-11jacksSLICEmbeddedprocessorModemInternetPhoneSystems52ThecodecinputsandoutputsgotooneormoreprocessorswheretheH.323orSIPprotocolisimplementedandwheretheDSPfunctionsforcompressionanddecompressionreside.編解碼器輸入和輸出進(jìn)入一個(gè)或多個(gè)處理器，在該處理器中實(shí)現(xiàn)H.323或SIP協(xié)議，也能實(shí)現(xiàn)用于壓縮和解壓縮的DSP功能。InternetPhoneSystems53EnterpriseIPPhones.SincemostemployeeswillalsohaveaPCconnectedtotheLAN,atwo-portEthernetswitchinthephoneorPCprovidesasingleEthernetconnectiontotheLANthatthephoneandPCshare.AmajorbenefitofIPphonesisthattheymayalsousewirelessEthernetconnections.AlreadysomecellphonemanufacturersareincludingWiFiVoIPinsomemodels.InternetPhoneSystems54Inthisway,aperson’scellphoneworksoutsidethecompanywiththestandardcellsiteservicebutalsoservesastheperson’scompanyphonewithawirelessEthernetconnectionwheninsidethecompany.通過這種方式，一個(gè)人的手機(jī)可以在公司外使用標(biāo)準(zhǔn)的手機(jī)站點(diǎn)服務(wù)，但在公司內(nèi)也可以作為個(gè)人的公司電話，通過無線以太網(wǎng)連接。Exercises551.Matchtheterms(1)-(6)withthedefinitionsA-F.(1)VoIPA.atelecommunicationnetworkwhichallowssubscribersatdifferentsitestocommunicatebyvoice.(2)PSTNB.alocaltelephonecompanyswitchingcenter(3)SS7C.amethodandgroupoftechnologiesforthedeliveryofvoicecommunicationsandmultimediasessionsoverInternetProtocolnetworks,suchastheInter