E1基础知识交流VIP免费

目录PCM&TDME1GeneralcharacteristicsE1FramingstructureE1AlarmBriefHistoryoftheEmergenceoftheDigitalSignalHierarchyTheneedtotransmitanalogvoiceoverdigitaltransmissionmediumresultedintheformationoftheDigitalSignalHierarchyinNorthAmericaintheearly1960’s.TheDS0constitutesthesmallestfundamentalunitintheDigitalSignalHierarchy.(8bitsx8kHz)64kbps.DigitalsignalhierarchyShorthistoryofpulsecodedmodulationPulseCodedModulation(PCM)•PCMisamethodbywhichanalogmessagecanbetransformedintonumericalformatandthendecodedatthereceiverPAM/HDB-3ChannelsamplingLP-filteringquantizationPulseregenerationLP-filteringPAM/HDB-3transmitterreceiverPCM-methodsummarized•AnalogspeechsignalisappliedintoaLP-filterrestrictingitsbandwidthinto3.4kHz•SamplingcircuitformsaPAMpulsetrainhavingrateof8kHz•Samplesarequantizedinto256levelsthatrequiresa8bit-wordforeachsample(28=256).•Thusatelephonesignalrequires8x8kHz=64kHzbandwidth•ThesamplesarelinecodedbyusingtheHDB-3schemetoalleviatesynchronizationproblemsatthereceiver•UsuallyonetransmitsseveralchannelssimultaneouslyfollowingSDHhierarchy(as30pcs)•Transmissionlinkcanbeanopticalfiber,radiolinkoranelectricalcable•AtthereceiverthePAMsignalisfirstreconstructedwhereafteritislowpassfilteredtoyieldtheoriginal-kind,analogsignalPCMsystemsanddigitaltimedivisionmultiplexing(TDM)•Indigitalmultiplexingseveralmessagesaretransmittedviasamephysicalchannel.Formultiplexing64kbit/schannelsindigitalexchangesfollowingthreemethodsarepopular:–PDH(plesio-synchronousdigitalhierarchy)(thedominantmethodtoday)(‘50-’60,G.702)–SONET(synchronousopticalnetwork)(‘85)–SDH(synchronousdigitalhierarchy)(CCITT‘88)EuropeanPCMframe32timeslotsx8bitsx8000Hz=2048kbit/sframesynchronizationslotsignalingortraffictraffic125sPDHE-1frameDigitalSignalHierarchy139.26Mbit/s139.26Mbit/s34.368Mbit/s34.368Mbit/s8.448Mbit/s8.448Mbit/s2.048Mbit/s2.048Mbit/s64kbit/s64kbit/sEuropeanhierarchyx4...x4x4x32139.26Mbit/s139.26Mbit/s44.736Mbit/s44.736Mbit/s6.312Mbit/s6.312Mbit/s1.544Mbit/s1.544Mbit/s64kbit/s64kbit/sUSAhierarchyx3...x7x4x24IfonewishestodisassembleatributaryfromthemainflowthemainflowmustbedemultiplexedstepbysteptothedesiredmainflowlevelinPDH.PCMHierarchyinPDHDigitaltransmissionsystems•InPSTNtwoPCMsystemsdominate:–T1,developedbyBellLaboratories,usedinUSA–E1,developedbyCEPT*usedinmostofothercountries•Inbothdatastreamsdividedinframesof8000frames/sec•InT1(E1)–24(32)timesslotsandaframing(F)bitserves24channels–Fbit(framesync)repeatsevery12frames–Framelength:1+8x24=193bits–Rate193x8000bits/second=1544kb/s–InE1TS0holdsasynchronizationpatternandTS16holdssignalinginformation–AnE1framehas32x8=256bitsanditsrateis8000x256=2048kb/s*EuropeanConferenceofPostalandTelecommunicationsAdministrationE1Generalcharacteristics•Nominalbitrate:2048kbit/s.•Bitrateaccuracy:±50ppm(±102.4bit/s).•Code:Highdensitybipolaroforder3(HDB3)•SummaryofE1GeneralSpecificationsPulseTemplateRequirementsBitStreamEncoding/DecodingInHDB3encoding,anysequenceoffourconsecutivezeroswillbereplacedby000VorB00V.ThechoiceismadesothatthenumberofBpulsesbetweenconsecutiveVpulsesisodd.SuccessiveVpulsesareofalternatepolaritytoavoidthepossibilityofaDCcomponent.TheE1framingstructureBasicframestructureat2048kbit/sSabitDescriptionoftheCRC-4procedureinbit1oftheframe•Wherethereisaneedtoprovideadditionalprotectionagainstsimulationoftheframe...