ip网络技术基础数据教程课件chapter2transmission media and codes

1ChapterTwoTransmissionMediaandCodes2IntroductionTheworldofcomputerswouldnotexistiftherewerenomediumbywhichtotransferdataThethreemajorcategoriesofmediainclude:ConductedmediaTwistedpairCoaxialCableOpticalfiberWirelessmediaChapterTwo–TransmissionMediaandCodes3Characteristicsandqualitydeterminedbymedium(immunitytointerference,bitrate,distance,frequency,signaletc.)Forguided,themediumismoreimportantForunguided,thebandwidthproducedbytheantennaismoreimportantKeyconcernsaredatarate,distanceandcostChapterTwo–TransmissionMediaandCodes4DesignFactorsBandwidthHigherbandwidthgiveshigherdatarateTransmissionimpairmentsAttenuationInterference5ConductiveMetalCOPPERElectricalconductivepropertiesMoreresistanttocorrosionthanotherconductingmetals6TwistedPairTwistedpairwireisclassifiedbycategory.TwistedpairiscurrentlyCategory1throughCategory7TwistingthewireshelpstoeliminateelectromagneticinterferencebetweenthetwowiresShieldingcanfurtherhelptoeliminateinterference7TwistedPair-ApplicationsMostcommonmediumTelephonenetworkBetweenhouseandlocalexchange(subscriberloop)WithinbuildingsToprivatebranchexchange(PBX)Forlocalareanetworks(LAN)10Mbpsor100Mbps8TwistedPair-ProsandConsCheapEasytoworkwithLowdatarateShortrange9TwistedPair-TransmissionCharacteristicsAnalogAmplifiersevery5kmto6kmDigitalUseeitheranalogordigitalsignalsrepeaterevery2kmor3kmLimiteddistanceLimitedbandwidth(1M)Limiteddatarate(100M)Susceptibletointerferenceandnoise10UnshieldedandShieldedTPUnshieldedTwistedPair(UTP)OrdinarytelephonewireCheapestEasiesttoinstallSuffersfromexternalEMinterferenceShieldedTwistedPair(STP)MetalbraidorsheathingthatreducesinterferenceMoreexpensiveHardertohandle(thick,heavy)11UTPCategoriesCat3upto16MHzVoicegradefoundinmostofficesCat4upto20MHzCat5upto100MHzCommonlypre-installedinnewofficebuildingsCat6Cat7table2.112CoaxialCableChapterTwo–TransmissionMediaandCodes13CoaxialCableApplicationsMostversatilemediumTelevisiondistributionCableTVLongdistancetelephonetransmissionCancarry10,000voicecallssimultaneouslyBeingreplacedbyfiberoptic/UTPShortdistancecomputersystemslinksLocalareanetworks14CoaxialCable-TransmissionCharacteristicsAnalogAmplifierseveryfewkm,closerifhigherfrequencyUpto500MHzDigitalRepeaterevery1km,closerforhigherdatarates15CoaxialCableBasebandcoaxialtechnologyusesdigitalsignalinginwhichthecablecarriesonlyonechannelofdigitaldataBroadbandcoaxialtechnologytransmitsanalogsignalsandiscapableofsupportingmultiplechannelsChapterTwo–TransmissionMediaandCodes16CoaxialCableChapterTwo–TransmissionMediaandCodes17ChapterTwo–TransmissionMediaandCodesOpticalFiber18OpticalFiber19OpticalFiber-ApplicationsLong-haultrunksMetropolitantrunksRuralexchangetrunksSubscriberloopsLANs20ItisverycommontomixfiberwithtwistedpairinLANsOpticalFiberChapterTwo–TransmissionMediaandCodes21OpticalFiber-TransmissionCharacteristicsActaswaveguidefor1014to1015HzPortionsofinfraredandvisiblespectrumLightEmittingDiode(LED)CheaperWideroperatingtemprangeLastlongerInjectionLaserDiode(ILD)MoreefficientGreaterdatarateWavelengthDivisionMultiplexing22OpticalFiberThickcablecausesmoreraycollisionsbecauseofmodaldispersion,soyouhavetotransmitslower.Thisisstepindexmultimodefiber.TypicallyuseLEDforlightsource,shorterdistancetransmissionsGradedindexmultimodefiberThincable–fasttransmission,typicallyusesalaser,longertransmissiondistances;knownassinglemodefiberChapterTwo–TransmissionMediaandCodes23OpticalFiber-BenefitsGreatercapacityDataratesofhundredsofGbpsSmallersize&weight(4.5-poundfibervs1600-poundcopperwire)Lowerattenuation(20miles)ElectromagneticisolationGreaterrepeaterspacing10sofkmatleastTransmissionCharacteristicsofGuidedMedia25WirelessMediaRadio,satellitetransmissions,andinfraredlightarealldifferentformsofelectromagneticwavesthatareusedtotransmitdataTechnicallyspeaking–inwirelesstransmissions,spaceisthemediumNoteinthefollowingfigurehoweachsourceoccupiesadifferentsetoffrequenciesChapterTwo–TransmissionMediaandCodesElectromagneticSpectrum27WirelessTransmissionFrequencies3x1011to2x1014InfraredLocal2GHzto40GHzMicrowaveHighlydirectionalPointtopointSatellite30MHzto1GHzOmnidirectionalBroadcastradio28TerrestrialMicrowaveParabolicdishFocusedbeamLineofsightLonghaultelecommunicationsHigherfrequenciesgivehigherdatarates29TerrestrialMicrowaveLand-based,line-of-sighttransmissionApproximately20-30milesbetweentowersTransmitsdataathundredofmillionsofbitspersecondSignalswillnotpassthroughsolidobjectsPopularwithtelephonecompaniesandbusinesstobusinesstransmissionsChapterTwo–TransmissionMediaandCodes30ChapterTwo–TransmissionMediaandCodes31SatelliteMicrowaveSatelliteisrelaystationSatellitereceivesononefrequency,amplifiesorrepeatssignalandtransmitsonanotherfrequencyTelevisionLongdistancetelephonePrivatebusinessnetworks32SatelliteMicrowaveSimilartoterrestrialmicrowaveexceptthesignaltravelsfromagroundstationonearthtoasatelliteandbacktoanothergroundstationCanalsotransmitsignalsfromonesatellitetoanotherSatellitescanbeclassifiedbyhowfaroutintoorbiteachoneis(LEO,MEO,GEO,andHEO)ChapterTwo–TransmissionMediaandCodes33SatelliteMicrowaveChapterTwo–TransmissionMediaandCodes34SatelliteMicrowaveLEO–LowEarthOrbit–100to1000milesout.Usedforwirelesse-mail,specialmobiletelephones,pagers,spying,videoconferencingGEO–GeosynchronousEarthOrbit–22,300miles.Alwaysoverthesamepositiononearth(andalwaysovertheequator).Usedforweather,television,governmentoperationsChapterTwo–TransmissionMediaandCodesSatellitePointtoPointLink36SatelliteBroadcastLink37ChapterTwo–TransmissionMediaandCodesWirelessLAN38WirelessLANTwobasiccomponentsnecessary:theclientradio,usuallyaPCcardwithanintegratedantennainstalledinalaptoporworkstation,andtheaccesspoint(AP),whichisanEthernetportplusatransceiver.TheAPactsasabridgebetweenthewiredandwirelessnetworksandcanperformbasicroutingfunctions.Workstationswithclientradiocardsresidewithinabasicserviceset,whilemultiplebasicservicesetscreateanextendedserviceset.ChapterTwo–TransmissionMediaandCodes39ChapterTwo–TransmissionMediaandCodes40WirelessLANIEEE802.11–Theoriginalwirelessstandard,capableoftransmittingdataat2MbpsIEEE802.11b–Thesecondwirelessstandard,capableoftransmittingdataat11MbpsInactualtests,11Mbps802.11bdevicesmanaged5.5Mbps(fromaJuly2000testbyNetworkComputing).ChapterTwo–TransmissionMediaandCodes41WirelessLANWithdirectionalantennaedesignedforpoint-to-pointtransmission,802.11bcantransmitformorethan10miles.Withanomni-directionalantennaonatypicalAP,rangemaydroptoaslittleas100feet.ChapterTwo–TransmissionMediaandCodes42WirelessLANIEEE802.11a–Oneofthemorerecentstandards,capableoftransmittingdataat54Mbps(theoretical)usingthe5GHzfrequencyrange.IEEE802.11g–Theotherrecentstandard,alsocapableoftransmittingdataat54Mbps(theoretical)butusingthesamefrequenciesas802.11b(2.4GHz)andisbackwardscompatiblewith802.11b.ChapterTwo–TransmissionMediaandCodes43BluetoothBluetoothwillenableuserstoconnecttoawiderangeofcomputingandtelecommunicationdeviceswithouttheneedofconnectingcablesTypicalusesincludephones,pagers,modems,LANaccessdevices,headsets,notebooks,desktopcomputers,andPDAsChapterTwo–TransmissionMediaandCodes44FreeSpaceOpticsUseslasers,ormoreeconomically,infraredtransmittingdevicesLineofsightbetweenbuildingsTypicallyshortdistances,suchasacrossthestreetCurrentspeedsgofromT-3(45Mbps)toOC-48(2.5Gbps)withfastersystemsindevelopmentChapterTwo–TransmissionMediaandCodes45FreeSpaceOpticsSafe,cheapNewerauto-trackingsystemskeeplasersalignedwhenbuildingsshakefromwindandtraffic(upto2.5km)Majorweaknessistransmissionthrufog(downtoacouplehundredmeters)Scintillationisalsoaproblem(especiallyinhotweather)ChapterTwo–TransmissionMediaandCodesChapterTwo–TransmissionMediaandCodes47MediaSelectionCriteriaCostSpeedDistanceandexpandabilityEnvironmentSecuritySummaryChapterTwo–TransmissionMediaandCodes48MediaSelectionCriteria-CostDifferenttypesofcostInitialcost–whatdoesaparticulartypeofmediumcosttopurchase?Toinstall?Maintenance/supportcostROI(returnoninvestment)–ifonemediumischeapertopurchaseandinstallbutisnotcosteffective,whereisthesavings?ChapterTwo–TransmissionMediaandCodes49MediaSelectionCriteria-SpeedTwodifferentformsofspeed:Propagationspeed–thetimetosendthefirstbitacrossthemedium.Thisspeeddependsuponthemedium.Airwavesandfiberarespeedoflight.CopperwireistwothirdsthespeedoflightDatatransferspeed–thetimetotransmittherestofthebitsinthemessage.ThisspeedismeasuredinbitspersecondChapterTwo–TransmissionMediaandCodes50MediaSelectionCriteria-DistanceandExpandabilityCanthischoiceofmediumbeexpandedeasily?Whatisneededtoextendthedistance?Arepeater?Anamplifier?Howmuchnoiseisintroducedwiththisexpansion?ChapterTwo–TransmissionMediaandCodes51MediaSelectionCriteria-EnvironmentIstheintendedenvironmentelectromagneticallynoisy?Ifso,shouldyouuseshielding?Orfiber?Ifusingwireless,arethereotherwirelesssignalsthatcaninterfere?Willthemicrowaveorfreespaceopticsbeaffectedbybadweather?ChapterTwo–TransmissionMediaandCodes52MediaSelectionCriteria-SecurityIsthemediumgoingtobecarryingsecuredata?Shouldyouworryaboutwiretapping?Encryptionofthesignal/datacanhelp,butmaynotbetheperfectsolution.ChapterTwo–Tr