The-Physical-LayerVIP免费

1ThePhysicalLayer2HighlightsSomeconceptsTransmissionmediumMessageswitch3SimplifiedDataCommunicationsModel4FundamentalConcepts(1)信道(Channel)：传送信息的媒体数据率(BitRate)：数据传输速率(bps)波特(Baud)：码元传输速率1Baud=(log2V)bps，其中V是信号的电平级数传播速度(PropagationSpeed)：通信线路上，信号单位时间内传送的距离（米/秒）带宽(Bandwidth)：信号占用的频率范围(Hz)信道容量(ChannelCapacity)：信道的最大数据率吞吐量(Throughput)：网络容量的度量，表示单位时间内网络可以传送的数据位数（bps）误码率BER(BitErrorRate)：信道传输可靠性指标P=传送错的位数/传送总位数5FundamentalConcepts(2)时延(Delay)：从向网络中发送数据块的第一比特开始，到最后一位数据被接收所经历的时间时延的组成：传播时延、发送时延、处理时延、排队时延传播时延：信号通过传输介质的时间。发送时延：设备发送一个数据块所需要的时间（数据块长度/信道带宽)处理时延：交换机/路由器检查数据、选路的时间排队时延：在交换机/路由器中排队等待的时间6SourcesofDelay(1)1.Nodalprocessingdelaycheckbiterrorsdetermineoutputlink2.Queueingdealy:timewaitingatoutputlinkfortransmissiondependsoncongestionlevelofrouter7SourcesofDelay(2)3.Transmissiondelay:R=linkbandwidth(bps)L=packetlength(bits)timetosendbitsintolink=L/R4.Propagationdelay:d=lengthofphysicallinks=propagationspeedinmediumpropagationdelay=d/s8Simplex,Half-duplex,Full-duplexSimplexTransmissionoccursinonlyonedirectioneg.FMRadiobroadcastingHalf-duplexTransmissioncanbemadeinbothdirection,butatonetimeonlyonedirectionisavailableeg.talkieandwalkie（对讲机）Full-duplexTransmissioncanbemadeinbothdirectionssimultaneouslyeg.Phoneconversation9Paralleltransmissionvs.Serialtransmission10AsynchronousTransmissionvs.SynchronousTransmission11同步串行传输和异步串行传输同步串行传输以时钟信号线对传输的数据线上的信号进行比特同步以数据块（帧或分组）为单位传输异步串行传输独立时钟，无须同步以字符为单位进行传输发送两个字符之间的间隔是任意的接收方依靠字符中的起始位和停止位来同步122.1TheTheoreticalBasisforDataCommunication13TheTheoreticalBasisforDataCommunicationFourierAnalysisBandwidth-LimitedSignalsMaximumDataRateofaChannel14FourierAnalysisT0T0nT0nn1nn1ndtg(t)/T2c2cos/T2bdtπnft)sin(2g(t)/T2a/T1fπnft),cos(2bπnft)sin(2a2c/g(t)πnft)dt(g(t)15Bandwidth-LimitedSignals(a)Abinarysignal(‘b’)anditsroot-mean-squareFourieramplitudes.(b)–(e)Successiveapproximationstotheoriginalsignal.16Bandwidth-LimitedSignals(2)Therangeoffrequenciestransmittedwithoutbeingstronglyattenuatediscalledthebandwidth.Forexample,atelephonewiremayhaveabandwidthof1MHzforshortdistances17Bandwidth-LimitedSignals(3)T=8/b,firstharmonicf=b/8voice-gradeline:Maxharmonics=3000/f=24000/bWhendatarates≥38.4kbps,thereisnohopeatallforbinarysignals,evenifthetransmissionfacilityiscompletelynoiseless.18BandwidthNotransmissionfacilitycantransmitsignalwithoutlosingsomepowerAlltransmissionfacilitiesdiminishdifferentFouriercomponentsbydifferentamountsRangeoffrequenciestransmittedwithoutbeingstrongly(0.5)attenuatediscalledbandwidthTelephonewire’sbandwidth:1MHzUTP5:100MHzbandwidthisaphysicalpropertyofthetransmissionmedium,dependsonconstructionthicknesslengthbandwidth(Hz,bps)19MaximumDataRateofaChannelNyquist'stheorem(1924)Ifasignalhasbeenrunthroughalow-passfilterofbandwidthH,thesignalcanbecompletelyreconst...