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首页 电信运作教程-Telecom Crash Course

电信运作教程-Telecom Crash Course.pdf

电信运作教程-Telecom Crash Course

fengli2009fly
2012-01-04 0人阅读 举报 0 0 暂无简介

简介:本文档为《电信运作教程-Telecom Crash Coursepdf》,可适用于IT/计算机领域

FirstThingsFirstCHAPTERSource:TelecomCrashCourseDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsiteTelecommunications,likeallhighlyvisibleandinterestingfields,isfullofapocryphalstories,technicalmyths,andfascinatinglegendsEveryoneinthefieldseemstoknowsomeonewhoknowstheoutsideplantrepairpersonwhofoundthepoisonoussnakeintheequipmentboxinthemanhole,thepersonwhowasonthecablelayingshipwhentheypulledupthecablethathadbeenbittenthroughbysomespeciesofdeepwatershark,somecollectionofseriouslyevilhackers,orthebackhoedriverwhocutthecablethatputLosAngelesofftheairforhoursThereisalsoacollectionoftechnojargonthatpervadesthetelecommnicationsindustryandoftengetsinthewayoftherelativelystraightforwardtaskoflearninghowallthisstuffactuallyworksToensurethatsuchthingsdon’tgetinthewayofabsorbingwhat’sinthisbook,I’dliketobeginwithadiscussionofsomeofthemThisisabookabouttelecommunications,whichisthescienceofcommunicatingoverdistance(te¯le,fromtheGreekte¯le,“faroff”)Itis,however,fundamentallydependentupondatacommunications,thescienceofmovingtrafficbetweencomputingdevicessothatthetrafficcanbemanipulatedinsomewaytomakeitusefulData,inandofitself,isnotparticularlyuseful,consistingasitdoesofastreamofonesandzeroesthatisonlymeaningfultothecomputingdevicethatwillreceiveandmanipulatethoseonesandzeroesThedatadoesnotreallybecomeusefuluntilitisconvertedbysomeapplicationintoinformation,becauseahumancangenerallyunderstandinformationThehumanthenactsupontheinformationusingaseriesofintuitiveprocessesthatfurtherconverttheinformationintoknowledge,atwhichpointitbecomestrulyusefulHere’sanexample:AcomputergeneratesasteadystreamofonesandzeroesinresponsetoaseriesofbusinessactivitiesinvolvingthecomputerthatgeneratestheonesandzeroesThoseonesandzeroesarefedintoanothercomputer,whereanapplicationconvertsthemintoaspreadsheetofsalesfigures(information)forthestorefromwhichtheyoriginatedAfinancialanalyststudiesthespreadsheet,calculatesafewratios,examinessomehistoricaldata(includingnotonlysalesnumbersbutdemographics,weatherpatterns,andpoliticaltrends),andmakesaninformedpredictionaboutfuturestockingrequirementsandadvertisingfocalpointsforthestorebasedontheknowledgethattheanalystwasabletocreatefromthedistilledinformationDatacommunicationsrelyonacarefullydesignedsetofrulesthatgovernsthemannerinwhichcomputersexchangedataTheserulesarecalledprotocols,andtheyarecentrallyimportanttothestudyofdataChapterIrealizethatthistermhasfallenoutoffavortoday,butIuseithereforhistoricalaccuracyFirstThingsFirstDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsitecommunicationsDictionariesdefineprotocolas“acodeofcorrectconduct”Fromtheperspectiveofdatacommunications,theydefineitas“astandardprocedureforregulatingthetransmissionofdatabetweencomputers,”whichisitself“acodeofcorrectconduct”Theseprotocols,whichwillbediscussedindetaillaterinthisbook,provideawidelyacceptedmethodologyforeverythingfromthepinassignmentsonphysicalconnectorstothesublimeencodingtechniquesusedinsecuretransmissionsystemsSimplyput,theyrepresentthemanyrulesetsthatgovernthegameManycountriesplayfootball,forexample,buttherulesareallslightlydifferentIntheUnitedStates,playersarerequiredtoweighmorethanacar,yetbeabletorunfasterthanoneInAustralianRulesfootball,thegameisdeclaredforfeitifitfailstoproduceatleastonebodypartamputationonthefieldorifatleastoneplayerdoesn’teatanotherTheyarebothfootball,howeverIndatacommunications,theproblemissimilartherearemanyprotocolsouttherethataccomplishthesamethingData,forexample,canbetransmittedfromonesideoftheworldtotheotherinavarietyofwaysincludingT,E,microwave,opticalfiber,satellite,coaxialcable,andeventhroughthewaterTheendresultisidentical:thedataarrivesatitsintendeddestinationDifferentprotocols,however,governtheprocessineachcaseAdiscussionofprotocolswouldbeincompletewithoutasimultaneousdiscussionofstandardsIfprotocolsarethevarioussetsofrulesbywhichthegameisplayed,standardsgovernwhichsetofruleswillbeappliedforaparticulargameForexample,let’sassumethatweneedtomovetrafficbetweenaPCandaprinterWeagreethatinorderforthePCtobeabletotransmitaprintablefiletotheprinter,bothsidesmustagreeonacommonrepresentationforthezeroesandonesthatmakeupthetransmitteddataTheyagree,forexample(andthisisonlyanexample)thattheywillbothrelyonaprotocolthatrepresentsazeroastheabsenceofvoltageandaoneasthepresenceofathreevoltpulseontheline,asshowninFigureBecausetheyagreeontherepresentation,theprinterknowswhenthePCissendingaoneandwhenthePCissendingazeroImaginewhatwouldhappeniftheyfailedtoagreeonsuchasimplethingbeforehandIfthetransmittingPCdecidestorepresentaoneasavoltpulseandtheprinterisexpectingathreevoltFirstThingsFirstFigureVoltagerepresentationsofdataFirstThingsFirstDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsitepulse,thetwodeviceswillhaveabrief(butinspired)conversation,theultimateresultofwhichwillbethereleaseofasmallpuffofsiliconsmokefromtheprinterNowtheyhavetodecideonastandardthattheywilluseforactuallyoriginatingandterminatingthedatathattheywillexchangeTheyareconnectedbyacable(seeFigure)thathasninepinsononeendandninejacksontheotherLogically,theinternalwiringofthecablewouldlooklikeFigureHowever,whenwestoptothinkaboutit,thisonetoonecorrespondenceofpintosocketwillnotworkIfthePCtransmitsonpin,whichinourexampleisidentifiedasthesenddatalead,itwillarriveattheprinteronpinthesenddataleadThiswouldbeanalogoustoholdingtwotelephonehandsetstogethersothattwocommunicatingpartiescantalkItwon’tworkwithoutagreatdealofholleringInstead,someagreementhastobeforgedtoensurethatthetrafficplacedonthesenddataleadsomehowarrivesonthereceivedataleadandviceversaSimilarly,theotherleadsmustbeabletoconveyinformationtotheotherendsothatnormaltransmissioncanbestartedandstoppedForexample,iftheprinterisreadytoreceivetheprintfile,itmightputvoltageonthedataterminalready(DTR)lead,whichsignalstothePCthatitisreadytoreceivetrafficThePCmightrespondbysettingitsownDTRleadhighasaformofacknowledgment,followedbyChapterSendData(pin)GroundCarrierDataSetReadyDataTerminalReadyReceiveDataRequesttoSendCleartoSendFigurePinassignmentsonacableconnectorFigureLogicalwiringschemeFirstThingsFirstDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsitetransmissionofthefilethatistobeprintedTheprinterwillkeepitsDTRleadhighuntilitwantsthePCtostopsendingForexample,iftheprintersensesthatitisrunningoutofbufferspacebecausethePCistransmittingfasterthantheslowerprintercanprint,itwilldroptheDTRlead,causingthePCtotemporarilyhaltitstransmissionoftheprintfileAssoonastheprinterisreadytoreceiveagain,itsetstheDTRleadhighonceagain,andprintingresumesAslongasboththetransmitterandthereceiverabidebythisstandardsetofrules,datacommunicationswillworkproperlyThisprocessofswappingthedataonthevariousleadsofacable,incidentally,isdonebythemodemorbyamodemcablethatmakesthecommunicatingdevicesthinktheyaretalkingtoamodemThemodemcableiswiredsothatthesenddataleadononeendisconnectedtothereceivedataleadontheotherendandviceversasimilarly,anumberofcontrolleadssuchasthecarrierdetectlead,theDTRlead,andthedatasetready(DSR)leadsarewiredtogethersothattheygivefalseindicationstoeachothertoindicatethattheyarereadytoproceedwiththetransmission,wheninfactnoresponsefromthefarendmodemhasbeenreceivedStandards:WhereDoTheyComeFromPhysicists,electricalengineers,andcomputerscientistsgenerallydesigndatacommunicationsprotocolsForexample,theTransmissionControlProtocol(TCP)andtheInternetProtocol(IP)werewrittenduringtheheadydaysoftheInternetbackinthesbysuchearlypioneersasVintonCerfandthelateJohnPostel(Iwanttosay“backinthelastcentury”tomakethemseemlikerealpioneers)Standards,ontheotherhand,arecreatedastheresultofaconsensusbuildingprocessthatcantakeyearstocompleteBydesign,standardsmustmeettherequirementsoftheentiredataandtelecommunicationsindustry,whichisofcourseglobalItmakessense,therefore,thatsomeinternationalbodyisresponsibleforoverseeingthecreationofinternationalstandardsOnesuchbodyistheUnitedNationsItsplusmembernationsworktogetherinanattempttoharmonizewhateverdifferencestheyhaveatvariouslevelsofinteraction,oneofwhichisinternationaltelecommunicationsTheInternationalTelecommunicationsUnion(ITU),asuborganizationoftheUN,isresponsiblefornotonlycoordinatingtheFirstThingsFirstFirstThingsFirstDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsitecreationofworldwidestandardsbutalsopublishingthemundertheauspicesofitsownsuborganizationsTheseincludetheTelecommunicationsStandardizationSector(TSS,sometimescalledtheITUT,andformerlytheConsultativeCommitteeonInternationalTelegraphyandTelephony,theCCITT),theTelecommunicationsDevelopmentSector(TDS),andtheRadioCommunicationSector(RCS,formerlytheConsultativeCommitteeonInternationalRadio,theCCIR)TheorganizationalstructureisshowninFigureOfcourse,theUNanditssuborganizationscannotperformthistaskalone,norshouldtheyInstead,theyrelyupontheinputofhundredsofindustryspecificorganizationsaswellaslocal,regional,national,andinternationalstandardsbodiesthatfeedinformation,perspectives,observations,andtechnicaldirectiontotheITU,whichservesasthecoordinationentityfortheoverallinternationalstandardscreationprocessTheseincludetheAmericanNationalStandardsInstitute(ANSI),theEuropeanTelecommunicationsStandardsInstitute(ETSI,formerlytheConferenceonEuropeanPostandTelegraph,CEPT),Telcordia(formerlyBellcore,nowpartofSAIC),theInternationalElectrotechnicalCommission(IEC),theEuropeanComputerManufacturersAssociation(ECMA),andahostofothersItisworthwhiletomentionabitabouttheITUasarepresentativestandardsbodyFoundedinaspartoftheUnitedNations,itdescendedfromamucholderbodycalledtheUnionTelegraphique,foundedinandcharteredtodevelopstandardsfortheemergingtelegraphindustryOvertheyearssinceitscreation,theITUanditsthreeprincipalmemberbodieshavedevelopedthreeprincipalgoals:■TomaintainandextendinternationalcooperationfortheimprovementandinterconnectivityofequipmentandsystemsthroughtheestablishmentoftechnicalstandardsChapterUNITUTDSTSSRCSFigureTheITUorganizationalstructureFirstThingsFirstDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsite■Topromotethedevelopmentofthetechnicalandnaturalfacilities(readspectrum)formostefficientapplications■Toharmonizetheactionsofnationalstandardsbodiestoattainthesecommonaims,andmostespeciallytoencouragethedevelopmentofcommunicationsfacilitiesindevelopingcountriesTheTelecommunicationsStandardizationSectorThegoalsoftheTSS,accordingtotheITU,areasfollows:■Tofulfillthepurposesoftheunionrelatingtotelecommunicationstandardizationbystudyingtechnical,operating,andtariffquestionsandadoptingformalrecommendationsonthemwithaviewtostandardizingtelecommunicationsonaworldwidebasis■Tomaintainandstrengthenitspreeminenceininternationalstandardizationbydevelopingrecommendationsrapidly■Todeveloprecommendationsthatacknowledgemarketandtraderelatedconsiderations■Toplayaleadingroleinthepromotionofcooperationamonginternationalandregionalstandardizationorganizationsandforumsandconsortiaconcernedwithtelecommunications■Toaddresscriticalissuesthatrelatetochangesduetocompetition,tariffprinciples,andaccountingpractices■TodeveloprecommendationsfornewtechnologiesandapplicationssuchasappropriateaspectsoftheGIIandGlobalmultimediaandmobilityTheTelecommunicationsStandardizationBureauTheTelecommunicationStandardizationBureauprovidessecretarialsupportfortheworkoftheITUTSectorandservicesfortheparticipantsinITUTwork,diffusesinformationoninternationaltelecommunicationsFirstThingsFirstFirstThingsFirstDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsiteworldwide,andestablishesagreementswithmanyinternationalstandardsdevelopmentorganizationsThesefunctionsinclude:■StudygroupmanagementThemanagementteamofthestudygroupsiscomposedofthechairman,vicechairmenofthestudygroup,chairmenoftheworkingparties,andtheTSBcounselorengineer■SecretarialsupportandmeetingorganizationTSBprovidessecretariatservicesforITUTassembliesandstudygroupmeetingsTSBcounselorsandengineerscoordinatetheworkoftheirstudygroupmeetings,andtheirassistantsensuretheflowofmeetingdocumentproduction■LogisticsservicesTheTSBprovidesservices,suchasmeetingroomallocation,registrationofparticipants,documentdistribution,andfacilitiesformeetingparticipants■ApprovalofrecommendationsandothertextsTheTSBorganizesandcoordinatestheapprovalprocessofrecommendations■AccesstoITUTdocumentsforITUTmembersTheTSBorganizesandcontrolsthedispatchofdocumentsinpaperformtoparticipantsinITUTworkandprovidesElectronicDocumentHandlingservices(EDH)thatenableeasyandrapidexchangeofdocuments,information,andideasamongITUTparticipantsinordertofacilitatetheworkofstandardsdevelopmentTheITUTparticipantscanhaveelectronicaccess,viaTIES,tostudygroupdocumentssuchasreports,contributions,delayedcontributions,temporaryandliaisondocuments,andsoonTheTSBalsoprovidesthefollowingservices:■MaintenanceoftheITUTWebsiteanddistributionofinformationabouttheactivitiesofthesectorincludingthescheduleofmeetings,TSBcirculars,collectiveletters,andallworkingdocuments■UpdateservicesforthelistofITUTrecommendations,theITUTworkprogrammerdatabase,theITUTpatentstatementsdatabase,andtheITUTtermsanddefinitionsdatabaseSectorAbbreviationsandDefinitionsforaTelecommunicationsThesaurusOrientedDatabase(SANCHO),aswellasupdateservicesforotherdatabasesasrequired■Countrycodenumberassignmentfortelephone,data,andotherservices■RegistrarservicesforUniversalInternationalFreephoneNumbers(UIFN)ChapterFirstThingsFirstDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsite■TechnicalinformationoninternationaltelecommunicationsandcollaboratescloselywiththeITUradiocommunicationsectorandwiththeITUtelecommunicationdevelopmentsectorformattersofinteresttodevelopingcountries■ProvidesadministrativeandoperationalinformationthroughtheITUOperationalBulletin■Coordinatestheediting,publication,andpostingoftherecommendationsTheRadioBureauThefunctionsoftheradiobureauinclude:■Administrativeandtechnicalsupporttoradiocommunicationconferences,radiocommunicationassembliesandstudygroups,includingworkingpartiesandtaskgroups■ApplicationoftheprovisionsoftheRadioRegulationsandvariousregionalagreements■Recordingandregistrationoffrequencyassignmentsandalsoorbitalcharacteristicsofspaceservicesandmaintenanceofthemasterinternationalfrequencyregister■Consultingservicestomemberstatesontheequitable,effective,andeconomicaluseoftheradiofrequencyspectrumandsatelliteorbits,andinvestigatesandassistsinresolvingcasesofharmfulinterference■Preparation,editing,anddispatchofcirculars,documents,andpublicationsdevelopedwithinthesector■Deliverstechnicalinformationandseminarsonnationalfrequencymanagementandradiocommunications,andworkscloselywiththetelecommunicationdevelopmentbureautoassistdevelopingcountriesTheStandardsAwordaboutthepublicationsoftheITUFirstofall,theyarereferredtoasrecommendationsbecausetheITUhasnoenforcementauthorityoverthemembernationsthatusethemItsstrongestinfluenceisexactlythattheabilitytoinfluenceitsmembertelecommunicationsauthoritiestousethestandardsbecauseitmakessensetodosoonaglobalbasisFirstThingsFirstFirstThingsFirstDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsiteThestandardsarepublishedeveryfouryears,followingenormouseffortonthepartoftherepresentativesthatsitontheorganization’staskforcesTheserepresentativeshailfromallcornersoftheindustrymostcountriesdesignatetheirnationaltelecommunicationscompany(wheretheystillexist)astherepresentativetotheITUT,whileothersdesignateanalternate,knownasaRecognizedPrivateOperatingAgency(RPOA)TheUnitedStates,forexample,hasdesignatedtheDepartmentofStateasitsdulyelectedrepresentativebodyOtherr

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电信运作教程-Telecom Crash Course

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