PhysicalLayer.ppt

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1、1ThePhysicalLayer物理层Chapter2DataTransmissionfromonehosttoanotheroneacrossthenetwork010111110000110101…ThePhysicalLayerperformsbitbybittransmissionoftheframesgiventoitbytheDataLinkLayer.Thespecifications技术规范ofthePhysicalLayerincludeMechanicalandelectric

2、alinterfaces(机械和电气接口)SocketsandwiresusedtoconnectthehosttothenetworkVoltagelevelsuses(e.g.-5Vand+5V)Encodingtechniques(编码技术),e.g.ManchesterencodingModulationtechniques(调制技术)usedTheoreticalBasisInformationcanbetransmittedonwiresbyvaryingsomephysicalprope

3、rty,suchasvoltage电压current电流.SignalTransmissionTwomethodsoftransmittingdata：AnalogsignalingDigitalsignalingDigitalSignaling数字信号编码Digitalsignalrepresentsdiscretestate(离散状态):onoroffPracticallyinstantaneouschange瞬间变化DigitalSignalingCurrentStateEncodingData

4、isencodingbythepresenceorabsenceofasignal数据按信号的有或无来编码ApositivevoltagemightrepresentabinaryoneorbinaryzeroThecurrentstateindicatesthevalueofthedataDigitalSignalingCurrentState当前状态DigitalSignalingStateTransition状态变迁AnalogSignaling模拟信号编码Signalsrepresentedb

5、yanelectromagneticwave电磁波SignaliscontinuousandrepresentsvaluesinarangeAnalogSignaling模拟信号编码UsesoneormoreofthecharacteristicsofananalogwavetorepresentonesandzerosThenumberofcompletewavecycleseverysecondisthefrequency频率.Themaximumintensityofawaveiscalledt

6、heamplitude振幅.PartsofaWave波的组成Thenumberofcompletewavecycleseverysecondisthefrequency频率.Themaximumintensityofawaveiscalledtheamplitude振幅.PartsofaWave波的组成PartsofaWave波的组成Thedistancebetweentwocrests(波峰)isthewavelength波长.Phase相位:Relativestateofonewavetoanot

7、herinregardstotimingAmplitude(a)Wavelength()orperiodPhasedifference()Thephasedifference相位差measures(asanangle)howfaraheadonewaveiswhencomparedtoanotherwave.ELECTROMAGNETICSPECTRUM电磁波频谱WavelengthFrequencyELECTROMAGNETICSPECTRUM电磁波频谱无线电微波红外线可见光紫外线X射线射线

8、双绞线同轴电缆卫星地面微波调幅无线电调频无线电海事无线电光纤电视f(Hz)f(Hz)LFMFHFVHFUHFSHFEHFTHF波段104105106107108109101010111012101310141015101610010210410610810101012101410161018102010221024移动无线电波长频率WirePropagationEffects传播效应PropagationEffectsSignalchangesasitt