通信及基础工程10

Unit13TextAStoredProgramControlStoredProgramControlStoredprogramcontrol(SPC)isatelecommunicationstechnologyusedfortelephoneexchangescontrolledbyacomputerprogramstoredinthememoryoftheswitchingsystem.SPCwastheenablingtechnologyofelectronicswitchingsystems(ESS)developedintheBellSystem[1]inthe1950s.TextTextWordsNotesDiscussionHomeEarlyexchangessuchasStrowger,panel,rotary,andcrossbarswitcheswereconstructedpurelyfromelectromechanicalswitchingcomponentswithanalogcontrolelectronics,andhadnocomputersoftwarecontrol.StoredprogramcontrolwasinventedbyBellLabs[2]scientistErnaSchneiderHooverin1954whoreasonedthatcomputersoftwarecouldcontroltheconnectionoftelephonecalls.TextTextWordsNotesDiscussionHomeSPCwasintroducedinelectronicswitchingsystemsinthe1960s.The101ESSPBXwasatransitionalswitchingsystemintheBellSystemtoprovideexpandedservicestobusinesscustomersthatwereotherwisestillservedbyanelectromechanicalcentralofficeswitch,whiletheWesternElectric1ESSswitchandtheAXEtelephoneexchangebyEricssonwerelarge-scalesystemsinthepublicswitchedtelephonenetwork.SPCenabledsophisticatedcallingfeatures.AsSPCexchangesevolved,reliabilityandversatilityincreased.Theadditionoftimedivisionmultiplexing(TDM)decreasedsubsystemsizesanddramaticallyincreasedthecapacityofthetelephonenetwork.Bythe1980s,SPCtechnologydominatedthetelecommunicationsindustry.TextWordsNotesDiscussionHome1.IntroductionTheprinciplefeatureofstoredprogramcontrolisoneormultipledigitalprocessingunits(storedprogramcomputers)thatexecuteasetofcomputerinstructions(program)storedinthememoryofthesystembywhichtelephoneconnectionsareestablished,maintained,andterminatedinassociatedelectroniccircuitry.TextWordsNotesDiscussionHomeAnimmediateconsequenceofstoredprogramcontrolisautomationofexchangefunctionsandintroductionofavarietyofnewtelephonyfeaturestosubscribers.TextWordsNotesDiscussionHomeAtelephoneexchangemustruncontinuouslywithoutinterruptionatalltimes,byimplementingafault-tolerantdesign.Earlytrialsofelectronicsandcomputersinthecontrolsubsystemsofanexchangeweresuccessfulandresultedinthedevelopmentoffullyelectronicsystems,inwhichtheswitchingnetworkwasalsoelectronic.AtrialsystemwithstoredprogramcontrolwasinstalledinMorris,Illinoisin1960.Itusedaflying-spotstorewithawordsizeof18bitsforsemi-permanentprogramandparameterstorage,andabarrier-gridmemoryforrandomaccessworkingmemory.Theworld’sfirstelectronicswitchingsystemforpermanentproductionuse,theNo.1ESS,wascommissionedbyAT&TatSuccasunna,NewJersey,inMay1965.By1974,AT&Thadinstalled475No.1ESSsystems.Inthe1980sSPCdisplacedelectromechanicalswitchinginthetelecommunicationindustry,hencethetermlostallbuthistoricalinterest.TodaySPCisastandardfeatureinallelectronicexchanges.TextWordsNotesDiscussionHomeTheattemptstoreplacetheelectromechanicalswitchingmatricesbysemiconductorcrosspointswitcheswerenotimmediatelysuccessful,particularlyinlargeexchanges.Asaresult,manyspacedivisionswitchingsystemsusedelectromechanicalswitchingnetworkswithSPC.Nonetheless,privateautomaticbranchexchanges(PABX)andsmallerexchangesdouseelectronicswitchingdevices.TextWordsNotesDiscussionHome2.TypesStoredprogramcontrolimplementationsmaybeorganizedintocentralizedanddistributedapproaches.Earlyelectronicswitchingsystems(ESS)developedinthe1960sand1970salmostinvariablyusedcentralizedcontrol.AlthoughmanypresentdayexchangedesigncontinuetousecentralizedSPC,withadventoflowcostpowerfulmicroprocessorsandVLSIchipssuchasprogrammablelogicarray(PLA)andprogrammablelogiccontrollers(PLC),distributedSPCbecamewidespreadbytheearly21stcentury.TextWordsNotesDiscussionHome(1)CentralizedcontrolIncentralizedcontrol,allcontrolequipmentisreplacedbyacentralprocessingunit.Itmustbeabletoprocess10to100callspersecond,dependingontheloadtothesystem.Multiprocessorconfigurationsarecommonplaceandmayoperateinvariousmodes,suchasinload-sharingconfiguration,insynchronousduplex-mode,oroneprocessormaybeinstand-bymode.TextWordsNotesDiscussionHome1)StandbymodeStandbymodeofoperationisthesimplestofadual-processorconfiguration.Normallyoneprocessorisinstandbymode.Thestandbyprocessorisbroughtonlineonlywhentheactiveprocessorfails.Animportantrequirementofthisconfigurationisabilityofstandbyprocessortoreconstitutethestateofexchangesystemwhenittakesoverthecontrol;meanstodeterminewhichofthesubscriberlinesortrunksareinuse.TextWordsNotesDiscussionHomeInsmallexchanges,thismaybepossiblebyscanningthestatussignalsassoonasthestandbyprocessorisbroughtintoaction.Insuchacaseonlythecallswhicharebeingestablishedatthetimeoffailurearedisturbed.Inlargeexchangesitisnotpossibletoscanallthestatussignalswithinasignificanttime.Heretheactiveprocessorcopiesthestatusofsystemperiodicallyintosecondarystorage.Whenswitchoveroccurstherecentstatusfromthesecondarymemoryisloaded.Inthiscaseonlythecallswhichchangestatusbetweenlastupdateandfailureareaffected.Thesharedsecondarystorageneednottobeduplicatedandsimpleunitlevelredundancywouldsuffice.1ESSswitchwasaprominentexample.TextWordsNotesDiscussionHome2)SynchronousduplexmodeInsynchronousduplexmodeofoperationhardwarecouplingisprovidedbetweentwoprocessorswhichexecutesamesetofinstructionsandcomparetheresultscontinuously.Ifmismatchoccursthenthefaultyprocessorisidentifiedandtakenoutofservicewithinafewmilliseconds.Whensystemisoperatingnormally,thetwoprocessorshavesamedatainmemoriesatalltimesandsimultaneouslyreceiveinformationfromexchangeenvironment.Oneoftheprocessoractuallycontrolstheexchange,buttheotherissynchronizedwiththeformerbutdoesnotparticipateintheexchangecontrol.(tobecontinued)TextWordsNotesDiscussionHome(Continued)Ifafaultisdetectedbythecomparatortheprocessorsaredecoupledandacheck-outprogramisrunindependentlytofindfaultyprocessor.Thisprocessrunswithoutdisturbingthecallprocessingwhichissuspendedtemporarily.Whenoneprocessoristakenoutthentheotherprocessoroperatesindependently.Whenthefaultyprocessorisrepairedandbroughtinservicethenmemorycontentsoftheactiveprocessorarecopiedintoitsmemoryandthetwoaresynchronizedandcomparatorisenabled.TextWordsNotesDiscussionHomeItispossiblethatacomparatorfaultoccursonlyduetotransientfailurewhichisnotshownevenwhencheckoutprogramisrun.Insuchcasethreepossibilitiesexists:·Continuewithbothprocessors·Takeouttheactiveprocessorandcontinuewiththeother.·Continuewithactiveprocessorbutremoveotherprocessorfromservice.TextWordsNotesDiscussionHomeScheme1isbasedontheassumptionthatthefaultistransientoneandmaynotappearagain.Inscheme2and3theprocessortakenoutissubjectedtoextensivetestingtoidentifyamarginalfailureinthesecases.TextWordsNotesDiscussionHome3)Load-sharingmodeInload-sharingoperation,anincomingcallisassignedrandomlyorinapredeterminedordertooneoftheprocessorswhichthenhandlesthecallrightthroughcompletion.Thus,boththeprocessorsareactivesimultaneouslyandsharetheloadandtheresourcesdynamically.Boththeprocessorshaveaccesstotheentireexchangeenvironmentwhichissensedaswellascontrolledbytheseprocessors.Sincethecallsarehandledindependentlybytheprocessors,theyhaveseparatememoriesforstoringtemporarycalldata.Althoughprogramsandsemi-permanentdatacanbeshared,theyarekeptinseparatememoriesforredundancypurposes.TextWordsNotesDiscussionHomeTheChineseandUSnetworkswillbothusedarkfiberstosendquantumkeys.Butthesefibers“arenotalwaysavailableandcanbeprohibitivelyexpensive”,saysAndrewShields,aquantumphysicistatToshibaResearchEuropeinCambridge,UK.Onewaytosidesteptheproblemistopiggybackthephotonstreamsontothe‘lit’fibersthattransmitconventionaltelecommunicationsdata.However,thoseconventionaldatastreamsareusuallyaboutamilliontimesstrongerthanquantumstreams,sothequantumdatatendtobedrownedout.TextWordsNotesDiscussionHomeThereisaninterprocessorlinkthroughwhichtheprocessorsexchangeinformationneededformutualcoordinationandverifyingthe'stateofhealth'oftheother.Iftheexchangeofinformationfails,oneoftheprocessorswhichdetectthesametakesovertheentireloadincludingthecallsthatarealreadysetupbythefailingprocessor.However,thecallsthatwerebeingestablishedbythefailingprocessorareusuallylost.Sharingofresourcescallsforanexclusionmechanismsothatboththeprocessorsdonotseekthesameresourceatthesametime.Themechanismmaybeimplementedinsoftwareorhardwareorboth.TextWordsNotesDiscussionHome(2)DistributedcontrolDistributedSPCisbothmoreavailableandmorereliablethancentralizedSSPCTextWordsNotesDiscussionHome1)VerticaldecompositionWholeexchangeisdividedintoseveralblocksandaprocessorisassignedtoeachblock.Thisprocessorperformsallthetaskrelatedtothatspecificblocks.Therefore,thetotalcontrolsystemconsistsofseveralcontrolunitscoupledtogether.Forredundancypurposeprocessormaybeduplicatedineachblocks.TextWordsNotesDiscussionHomeHecalculatesthatitwouldbepossibletosendQKDsignalsalongside40conventionaldatachannels.Opticalfibersusuallycarrybetween40and160telecommunicationschannels,meaningthatquantumcommunicationcouldbecarriedoutwithexistinginfrastructure.TextWordsNotesDiscussionHome2)HorizontalDecompositionInthistypeofdecompositioneachprocessorperformsonlyoneorsomeexchangefunction.TextWordsNotesDiscussionHomememoryn.[计]存储器，内存；记忆，

paneln.仪表板；嵌板rotaryadj.&n.旋转的，转动的；[动力]转缸式发动机crossbarn.横木；横条；横梁，横档electromechanicaladj.[电][机]电动机械的transitionaladj.渐变的，转变的；变迁的WordsWordsTextWordsNotesDiscussionHomeversatilityn.多用途；可转动性executevt.执行；处死，处决parametern.参数；参量；限制因素barrier-gridn.障栅commissionvt.委任，授予；使服役displacevt.移动，移走；替换，取代WordsTextWordsNotesDiscussionHomeprogrammableadj.可设计的，可编程的duplexadj.有两部分的standbyn.&adj.备用品；备用的reconstitutevt.再组成，再构成sufficev.足够；有能力duplicatev.&adj.复制；重复；完全一样的WordsTextWordsNotesDiscussionHomeredundancyn.（机器的）多余度；过多synchronousadj.同时存在[发生]的synchronizevt.使同步；使同时comparatorn.比较仪，比较器；比测器transientadj.短暂的；转瞬即逝的predeterminev.预先裁定；注定

couplev.连在一起，连接decompositionn.分解；腐烂WordsTextWordsNotesDiscussionHome[1]BellSystem：贝尔本人创立的贝尔电话公司曾形成庞大的贝尔系统（BellSystem），并垄断美国的电信事业达百年之久，贝尔系统以AT&T公司为母公司，下属众多子公司和研究所。TextWordsNotesDiscussionNotesHome[2]BellLabs：美国贝尔实验室是晶体管、激光器、太阳能电池、发光二极管、数字交换机、通信卫星、电子数字计算机、蜂窝移动通信设备、长途电视传送、仿真语言、有声电影、立体声录音，以及通信网等许多重大发明的诞生地。自1925年以来，贝尔实验室共获得两万五千多项专利，现在，平均每个工作日获得三项多专利。TextWordsNotesDiscussionHomeQuestionsfordiscussion1.WhatisStoredProgramControl?2.WhatmainfeaturedoesSPCbear?3.HowmanycategoriesdoesSPCfallinto?Whatarethey?4.Whatisstandbymode?TextWordsNotesDiscussionHomeAnswerstoquestionsfordiscussionTextWordsNotesDiscussionHome1.WhatisStoredProgramControl?Storedprogramcontrol(SPC)isatelecommunicationstechnologyusedfortelephoneexchangescontrolledbyacomputerprogramstoredinthememoryoftheswitchingsystem.SPCwastheenablingtechnologyofelectronicswitchingsystems(ESS)developedintheBellSysteminthe1950s.TextWordsNotesDiscussionHome2.WhatmainfeaturedoesSPCbear?ThemainfeatureofSPCisoneormultipledigitalprocessingunits(storedprogramcomputers)thatexecuteasetofcomputerinstruct