几种类型的多路复用技术ppt课件.ppt

DataandComputerCommunications Chapter8Multiplexing 为充分利用通信干线的传输容量 常采用多路复用技术 多路器 复用器 组合N路输入线路上的数据 通过一条高容量的数据链路传输 分路器接收到复用的数据流 按通道分离 分路 这些数据 把它们送到适当的输出线路上 多路复用 几种类型的多路复用技术 频分多路复用 FDM 在无线电和电视机技术中广为使用 同步时分多路复用 TDM 时分多路复用的特殊情况 常被称为TDM 普遍用于多路复用数字语音流的传输 统计TDM通过在多路器上增加一些复杂处理提高同步TDM的效率 各种熟悉的名称包括 统计TDM 异步TDM 智能TDM 统计TDM的名称指出了它的主要特性 频分多路复用 a 发送器 b 复合信号的谱 正f 频分多路复用 c 接收器 频分复用 波分复用 FDM的变形 时分复用 复用 共享使用公共信道 DEMUX 复用器 解复用器 共享信道 Multiplexing 8 1FrequencyDivisionMultiplexing 1 FDM频分复用Usefulbandwidthofmediumexceedsrequiredbandwidthofchannel在传输媒体的有效带宽超出信道需要的带宽时 就可以使用FDMEachsignalismodulatedtoadifferentcarrierfrequency每一个信号调制到不同的载波频率 FrequencyDivisionMultiplexing 2 Carrierfrequenciesseparatedsosignalsdonotoverlap guardbands 载波频率要相互隔离使信号不重叠 防护频带 e g broadcastradioChannelallocatedevenifnodata FrequencyDivisionMultiplexingDiagram FDMSystem FDMofThreeVoicebandSignals AnalogCarrierSystems 1 AT T USA 美国电话电报公司HierarchyofFDMschemesGroup 基群 12voicechannels 4kHzeach 48kHzRange60kHzto108kHz AnalogCarrierSystems 2 Supergroup 超群 60channelFDMof5groupsignalsoncarriersbetween420kHzand612kHzMastergroup 主群 10supergroups 8 2SynchronousTimeDivisionMultiplexing DatarateofmediumexceedsdatarateofdigitalsignaltobetransmittedMultipledigitalsignalsinterleavedintimeMaybeatbitlevelofblocksTimeslotspre assignedtosourcesandfixedTimeslotsallocatedevenifnodataTimeslotsdonothavetobeevenlydistributedamongstsources 不必在数据源间均匀分配时隙 TimeDivisionMultiplexing TDMSystem TDMLinkControl Noheadersandtailers 传输数据流无首尾部 DatalinkcontrolprotocolsnotneededFlowcontrolDatarateofmultiplexedlineisfixedIfonechannelreceivercannotreceivedata theothersmustcarryonThecorrespondingsourcemustbequenchedThisleavesemptyslotsErrorcontrolErrorsaredetectedandhandledbyindividualchannelsystems DataLinkControlonTDM Framing NoflagorSYNCcharactersbracketingTDMframes 无标志或SYNC对TDM定界 MustprovidesynchronizingmechanismAddeddigitframing 增加数字组帧 OnecontrolbitaddedtoeachTDMframeLookslikeanotherchannel controlchannel Identifiablebitpatternusedoncontrolchannele g alternating01010101 unlikelyonadatachannelCancompareincomingbitpatternsoneachchannelwithsyncpattern Addeddigitframing 增加数字组帧 OnecontrolbitaddedtoeachTDMframeLookslikeanotherchannel controlchannel 每一帧附加一控制位 看起来像另一个信道 控制信道Identifiablebitpatternusedoncontrolchannel控制信道使用可标示位模式e g alternating01010101 unlikelyonadatachannel如数据信道不太可能的交替位模式01010101Cancompareincomingbitpatternsoneachchannelwithsyncpattern PulseStuffing 脉冲填充 Problem SynchronizingvariousdatasourcesClocksindifferentsourcesdriftingDataratesfromdifferentsourcesnotrelatedbysimplerationalnumberSolution PulseStuffingOutgoingdatarate excludingframingbits higherthansumofincomingratesStuffextradummybitsorpulsesintoeachincomingsignaluntilitmatcheslocalclockStuffedpulsesinsertedatfixedlocationsinframeandremovedatdemultiplexer Solution PulseStuffing Outgoingdatarate excludingframingbits higherthansumofincomingrates输出数据速率 不含帧定位比特 高于进入数据速率和Stuffextradummybitsorpulsesintoeachincomingsignaluntilitmatcheslocalclock对每一个输入填充额外空比特或脉冲直到匹配本地时钟Stuffedpulsesinsertedatfixedlocationsinframeandremovedatdemultiplexer填充脉冲被插入帧中固定位置使分用器能删除之 TDMofAnalogandDigitalSources DigitalCarrierSystems HierarchyofTDMUSA Canada JapanuseonesystemITU Tuseasimilar butdifferent systemUSsystembasedonDS 1formatMultiplexes24channelsEachframehas8bitsperchannelplusoneframingbit193bitsperframe DigitalCarrierSystems 2 Forvoiceeachchannelcontainsonewordofdigitizeddata PCM 8000samplespersec Datarate8000 x193 1 544MbpsFiveoutofsixframeshave8bitPCMsamplesSixthframeis7bitPCMwordplussignalingbitSignalingbitsformstreamforeachchannelcontainingcontrolandroutinginfoSameformatfordigitaldata23channelsofdata7bitsperframeplusindicatorbitfordataorsystemscontrol24thchannelissync MixedData DS 1cancarrymixedvoiceanddatasignals24channelsusedNosyncbyteCanalsointerleaveDS 1channelsDs 2isfourDS 1giving6 312Mbps ISDNUserNetworkInterface ISDNallowsmultiplexingofdevicesoversingleISDNlineTwointerfacesBasicISDNInterfacePrimaryISDNInterface BasicISDNInterface 1 DigitaldataexchangedbetweensubscriberandNTE FullDuplexSeparatephysicallineforeachdirectionPseudoternarycodingscheme1 novoltage 0 positiveornegative750mV 10 Datarate192kbpsBasicaccessistwo64kbpsBchannelsandone16kbpsDchannelThisgives144kbpsmultiplexedover192kbpsRemainingcapacityusedforframingandsync BasicISDNInterface 2 BchannelisbasiciserchannelDataPCMvoiceSeparatelogical64kbpsconnectionsodifferentdestinationsDchannelusedforcontrolordataLAPDframesEachframe48bitslongOneframeevery250 s FrameStructure PrimaryISDN PointtopointTypicallysupportingPBX1 544MbpsBasedonUSDS 1UsedonT1services23BplusoneDchannel2 048MbpsBasedonEuropeanstandards30BplusoneDchannelLinecodingisAMIusingHDB3 PrimaryISDNFrameFormats Sonet SDH SynchronousOpticalNetwork ANSI SynchronousDigitalHierarchy ITU T CompatibleSignalHierarchySynchronousTransportSignallevel1 STS 1 orOpticalCarrierlevel1 OC 1 51 84MbpsCarryDS 3orgroupoflowerratesignals DS1DS1CDS2 plusITU Trates e g 2 048Mbps MultipleSTS 1combinedintoSTS NsignalITU Tlowestrateis155 52Mbps STM 1 SDH 同步数字体系 和SONET 同步光网络 技术要点由标准的网络单元组成统一的NNI 简化了信号的互通 传输 复用 交叉连接和交换标准的信息速率等级标准的光接口特殊的复用结构 PDH B ISDN信号都可以进入环形网络结构 可靠 路由灵活帧中有大量开销位 软件进行网络配置和控制使用单个主时钟来同步核心特点同步复用标准光接口强大的网络管理能力 速率等级 SONETSDH比特率 Mbps STS 1 OC 151 84STS 3 OC 3STM 1155 52STS 9 OC 9STM 3466 56STS 12 OC 12STM 4622 08STS 18 OC 18STM 6933 12STS 24 OC 24STM 81244 16STS 36 OC 36STM 121866 24STS 48 OC 48STM 162488 32STS SynchronousTransportSignal同步传输信号OC OpticalCarrier光载波STM SynchronousTransportModule同步传输模块 SONET系统 包含交换机 复用器和中继器 Section 段 任意两个相邻设备之间的光纤line 线路 两个复用器之间path 通道 源站和目的站之间 端到端 SONETFrameFormat SONETSTS 1OverheadOctets 8 3StatisticalTDM InSynchronousTDMmanyslotsarewastedStatisticalTDMallocatestimeslotsdynamicallybasedondemandMultiplexerscansinputlinesandcollectsdatauntilframefullDatarateonlinelowerthanaggregateratesofinputlines StatisticalTDMFrameFormats Performance OutputdataratelessthanaggregateinputratesMaycauseproblemsduringpeakperiodsBufferinputsKeepbuffersizetominimumtoreducedelay BufferSizeandDelay 8 4AsymmetricalDigitalSubscriberLine ADSLLinkbetweensubsc