《cisco教材》PPT课件

1Presentation_ID©1999,CiscoSystems,Inc.CableSolutionsTrainingProgramForUniversalBroadbandRouterandCableModem2CiscoSystemsConfidentialVisualizingaDOCSISoverHFCNetwork100ChannelsHeadendCOAXTapDropNodeHubHubNodeNodeCableModemPCNodeNodeNodeNodeNodeHubBroadbandRouteruBR7246TotalNetworkManagementPSTNInternetCNNHBOESPNFNNNodeDOWNSTREAM88-880MHzUPSTREAM5-42MHz3CiscoSystemsConfidentialAccessinfrastructureServiceProviderCustomerPremisesPOTSISP1ISP2WirelessSONET/ATMBackboneCompACompBSwitchISDNServices:InternetAccessOn-lineServiceTelecommutingCableHead-EndD/CD/CCableHDSLADSLVDSLFanoutShelfD/CD/CNewAccessService54CiscoSystemsConfidentialSimpleLabTopologyuBR7223USDSIFRFUpconvertorDiplexFilteruBR904Legend:DownstreamUpstreamBi-directional10BaseTHubDHCP/DNS/TOD/TFTPServerTelnetConnectionConsoleConnectionATTATTHiLoADCBATTATTATTVariableAttenuater303063RepeatforB,C,DtoUSports1,2,35Presentation_ID©1999,CiscoSystems,Inc.Module2CATVandRFTechnologyOverview6CiscoSystemsConfidentialTerms•CATV-CommunityAntennaTV•NTSC-NationalTelevisionSystemsCommittee:U.S.TVtechnicalstandard,namedaftertheorganizationthatcreateditin1941.Usesa6MHzwidemodulatedsignal•PAL-PhaseAlternatingLine.TheTVsystemusedinmostofEuropeandmanyotherplaces,inwhichthecolorcarrierphasedefinitionchangesinalternatescanlines.Utilizesan8MHzwidemodulatedsignal•SECAM-TVsystemusedinFranceandsomeformerSovietbloccountries.Utilizesan8MHzwidemodulatedSignal.•SpectrumReuse-CATV’smostfundamentalconceptisspectrumreuse.Historically,theover-the-airspectrumhasbeenassignedtomanyotherpurposes.MuchofitisthereforenotavailableforthecarriageofTV.Theresultisaninadequatesupplyofspectrumtoserveviewersneeds.Cablecanreusespectrumthatissealedinitsaluminumtubes.•CoaxialCable-TheprincipalphysicalmediaoverwhichCATVsystemsarebuilt.ThemaindrawbackofCoaxCableisit’srelativelyhighloss.Coaxsignallossisafunctionofitsdiameter,dielectricconstruction,temperature,andoperatingfrequency(f)7CiscoSystemsConfidentialTerms•Carrier-to-Noise-C/N(alsoCNR):ThedifferenceinamplitudebetweenthedesiredRFcarrierandthenoiseinthatportionofthespectrum•Signal-to-Noise-S/N(alsoSNR):SimilartoC/NbutrelatestoaBaseBandsignal•IngressNoise-Over-the-airsignalsthatareinadvertentlycoupledintothenominallyclosedcoaxialcabledistributionsystem.Difficulttotrackdownandintermittentinnature.•QPSK-QuadraturePhaseShiftKeying.Adigitalmodulationmethodinwhichthethereare2databitsrepresentedwitheachbaudsymbol.•QAM-QuadratureAmplitudeModulation.Adigitalmodulationmethodinwhichthevalueofasymbolconsistingofmultiplebitsisrepresentedbyamplitudeandphasestatesofacarrier.TypicalQAMtypesare16-QAM(4bitspersymbol),64-QAM(6bitspersymbol),and256-QAM(8bitspersymbol)•Downstream(DS)-Signalflowfromheadendtowardsubscribers.AlsocalledForwardPath•Upstream(US)-SignalflowfromthesubscriberstotheHeadend.AlsocalledtheReturnorReversePath8CiscoSystemsConfidentialTerms•Carrier-orRFcarrier.Asignalonwhichanother,lower-frequencysignalismodulatedinordertotransportthelower-frequencysignaltoanotherlocation.•FDM-FrequencyDivisionMultiplexing.Adatatransmissionmethodinwhichanumberoftransmittersshareatransmissionmedium,eachoccupyingadifferentfrequency.•Headend-ThelocationwheretheCablecompanyaggregates,combines,mixes,andmodulatesallsignalsinordertosendthemdownstreamandreceiveupstreamsignals•Broadband-Referstotheabilitytofrequencydivisionmultiplex(FDM)manysignalsinawideRFbandwidthoveranHFCnetwork,andtheabilitytovastamountsofinformation.•FEC-ForwardErrorCorrection.Indatatransmission,aprocessbywhichadditionaldataisaddedthatisderivedfromthepayloadbyanassignedalgorithm.Itallowsthereceivertodetermineifcertainclassesoferrorshaveoccurredintransmissionand,insomecases,allowsotherclassesoferrorstobecorrected.9CiscoSystemsConfidentialMeasurementUnits•dB-Decibel.Ameasureoftherelativestrengthoftwosignals.MultiplicationbecomesadditionandDivisionbecomessubtraction.•dBm-Decibelswithrespecttoonemilliwatt.AunitofRFsignalstrengthusedinsatelliteworkandothercommunicationsapplications•dBmV-Decibelswithrespectto1millivoltina75-ohmsystem.TheunitofRFpowerusedinCATVindustry.•0dBmV=1millivoltmeasuredacrossanimpedanceof75ohms.10CiscoSystemsConfidentialDevicesandSymbolsHeadEndFibreSatelliteAntennaVHF/UHFAntennaRFAmplifierBi-DirectionalAmplifierSplitter8-WayTapFibreTransmitterFibreNode11Presentation_ID©1999,CiscoSystems,Inc.BasicCATVComponents,ConceptsandTopology12CiscoSystemsConfidentialRFSpectrum•RadioFrequency(RF)AboveAudiotoInfraRed•DownStream(DS)(Forward)Cablecompanytosubscriber55-750(860)MHzFrequency110/220VElectricalSignal60HzIF5-45MHzRF(VHF&UHF)55-750MHzMicrowaveAbove1GHzInfraRedVisibleLightUltraVioletX-RaysGammaRaysCB27MHzChannel255MHzSatelliteFrequencySpectrum•UpStream(US)(Reverse)•SubscribertoCablecompany•5-42(30)MHzNote:NonNorthAmericansystemscanhavedifferentcutofffrequenciessuchas65MHz,88Mhz105Mhzetc.13CiscoSystemsConfidentialCOAXIALCABLETRANSMISSIONSYSTEMSCOAXIALCABLEandPROPERTIESDIRECTCURRENTALTERNATINGCURRENTIncreasingFrequencyForDirectCurrent,electronflowisdistributeduniformlythroughouttheconductor.Asfrequencyi