计算机网络专业英语 课件 Lesson 8 Cables,Connectors and Wireless Links

L8-1

Lesson8

Cables,ConnectorsandWirelessLinksText1

TwistedPair要点KeyPoints：粗/细Apply/use/implement属性/特性/性能Mbps、mb/sEMI/屏蔽/辐射/抵消快速以太网、吉比特以太网、万兆线对/线束插座/头的结构Oneoftheoldestandstillmostcommontransmissionmediaistwistedpair.atwistedpairconsistsoftwoinsulatedcopperwires,typicallyabout1mmthick.Thewiresaretwistedtogetherinahelicalform.Twistingisdonebecausetwoparallelwiresconstituteafineantenna.Whenthewiresaretwisted,thewavesfromdifferenttwistscancelout,sothewireradiateslesseffectively.Twistedpairscanbeusedfortransmittingeitheranalogordigitalsignals.Thebandwidthdependsonthethicknessofthewireandthedistancetraveled,butseveralMb/stotensofMb/scanbeachievedforafewkilometersinmanycases.Thefrequencyrangeoftwisted-paircablesisapproximately0to10GHz.Duetotheiradequatepropertiesandlowcost,twistedpairsarewidelyusedandarelikelytoremainsoforyearstocome.Twistedpaircablesareoften

shielded

inattempttopreventelectromagneticinterference(EMI).Becausetheshieldingismadeofmetal,itmayalsoserveasaground.However,usuallyashieldedorascreenedtwistedpaircablehasaspecialgroundingwireaddedcalledadrainwire.Thisshieldingcanbeappliedtoindividualpairs,ortothecollectionofpairs.Whenshieldingisappliedtothecollectionofpairs,thisisreferredtoasscreening.Theshieldingmustbegroundedfortheshieldingtowork.IncontrasttoFTP(foiledtwistedpair)andSTP(shieldedtwistedpair)cabling,UTP(unshieldedtwistedpair)cableisnotsurroundedbyanyshielding.Itistheprimarywiretypefortelephone

usageandcomputernetworking,especiallyaspatchcables.UTPcomesinseveralvarieties:Category3:WastheearliestsuccessfulimplementationofUTP.It’sprimarilyusedforvoiceandlower-speeddataapplications.Category5e:Withtheneedforhigherspeeds,GigabitEthernethasbecomethenewreplacementforFastEthernet.Tomakeitwork,Cat5eextendsthelifeofCat5cable.Itcanrunatamaximumof1,000Mbps.Category6:Cat5ecanrunatgigabitspeeds,butwith10-GigabitEthernetonthehorizon,Cat5ehasstretchedtheCat5standardtoitslimits.Cat6cancurrentlyrunat1,000Mbps(1Gbps).TheCategory6specificationwasreleasedforpublicationveryrecently,howeverasdesigned,Category6cablingwillbeabletosupportspeedsuptoatleast10Gbps.ThestandardconnectorforUTPcablingisanRJ-45connector.Thisisaplasticconnectorthatlookslikealargetelephone-styleconnector.AslotallowstheRJ-45tobeinsertedonlyoneway.RJstandsforRegisteredJack.1mmthickThethicknessofwiresis1mm1mmindiameteruse/usageapply/applicationapplianceImplement/implementationProperty（可数）属性、性质、财产、性能Character/characteristic/feature特性Performance性能Shield名：盾动：屏蔽Shielding名：屏蔽

Itcanrunatamaximumof1,000Mbps.upto1000Mbpsuptoatleast10GbpsThecollectionofpairs双绞线束A

twistedpair绞线对Individualpairs每对线parallelwiresconstituteafineantennaDrainWire 引流线FTP(foiledtwistedpair)twistedpaircablehasaspecialgroundingwireaddedcalledadrainwire.ThisshieldingcanbeSerialportParallelportgroundingwireOneoftheoldestandstillmostcommontransmissionmediaistwistedpair.atwistedpairconsistsoftwoinsulatedcopperwires,typicallyabout1mmthick.Thewiresaretwistedtogetherinahelicalform.Twistingisdonebecausetwoparallelwiresconstituteafineantenna.Whenthewiresaretwisted,thewavesfromdifferenttwistscancelout,sothewireradiateslesseffectively.Twistedpairscanbeusedfortransmittingeitheranalogordigitalsignals.Thebandwidthdependsonthethicknessofthewireandthedistancetraveled,butseveralMb/stotensofMb/scanbeachievedforafewkilometersinmanycases.Thefrequencyrangeoftwisted-paircablesisapproximately0to10000MHz.Duetotheiradequatepropertiesandlowcost,twistedpairsarewidelyusedandarelikelytoremainsoforyearstocome.Twistedpaircablesareoftenshieldedinattempttopreventelectromagneticinterference(EMI).Becausetheshieldingismadeofmetal,itmayalsoserveasaground.However,usuallyashieldedorascreenedtwistedpaircablehasaspecialgroundingwireaddedcalledadrainwire.Thisshieldingcanbeappliedtoindividualpairs,ortothecollectionofpairs.Whenshieldingisappliedtothecollectionofpairs,thisisreferredtoasscreening.Theshieldingmustbegroundedfortheshieldingtowork.IncontrasttoFTP(foiledtwistedpair)andSTP(shieldedtwistedpair)cabling,UTP(unshieldedtwistedpair)cableisnotsurroundedbyanyshielding.Itistheprimarywiretypefortelephoneusageandcomputernetworking,especiallyaspatchcables.UTPcomesinseveralvarieties:Category3:WastheearliestsuccessfulimplementationofUTP.It’sprimarily

usedforvoiceandlower-speeddataapplications.Category5e:Withtheneedforhigherspeeds,GigabitEthernethasbecomethenewreplacementforFastEthernet.Tomakeitwork,Cat5eextendsthelifeofCat5cable.Itcanrunatamaximumof1,000Mbps.Category6:Cat5ecanrunatgigabitspeeds,butwith10-Gigabit

Ethernetonthehorizon,Cat5ehasstretched

theCat5standardtoitslimits.Cat6cancurrentlyrunat1,000Mbps(1Gbps).TheCategory6specificationwasreleasedforpublicationveryrecently,howeverasdesigned,Category6cablingwillbeabletosupportspeedsuptoatleast10Gbps.ThestandardconnectorforUTPcablingisanRJ-45connector.Thisisaplasticconnectorthatlookslikealargetelephone-styleconnector(seeFigure8-2).AslotallowstheRJ-45tobeinsertedonlyoneway.RJstandsforRegisteredJack.Variety多样化，变化Vary（动）inavarietyofways用种种方法Initial最初的、字首的（顺序）Original原来的、首创的（起源）Primitive原始的、最早的、初期的（顺序+起源）Primary主要的、初级的Extend延伸Stretch伸展Expand扩展FastEthernetGigabitEthernet10-GigabitEthernetThewavesfromdifferenttwistscancelout,sothewireradiateslesseffectively.Socket/jack/outletPlugSlot/jackWallboxFaceplateSwitchRJstandsforRegisteredJack.千斤顶，（电）插孔，插座Slot狭槽、放入插槽（动）Plug插头、插入（动）Insert插座socket、outlet出口L8-2

Lesson8

Cables,ConnectorsandWirelessLinksText2OpticalFiber要点KeyPoints：比特1/0Ultra转变、

产生、完成损耗微米安全光纤/缆的结构比较单模和多模光纤Anopticaltransmissionsystemhasthreekeycomponents:thelightsource,thetransmissionmedium,andthedetector.Conventionally,apulseoflightindicatesa1bitandtheabsenceoflightindicatesa0bit.Thetransmissionmediumisanultra-thinfiberofglassorplastic.Thedetectorgeneratesanelectricalpulsewhenlightfallsonit.Byattachingalightsourcetooneendofanopticalfiberandadetectortotheother,wehaveaunidirectionaldatatransmissionsystemthatacceptsanelectricalsignal,convertsandtransmitsitbylightpulses,andthenreconvertstheoutputtoanelectricalsignalatthereceivingend.Higherbandwidthlinkscanbeachievedusingopticalfibers.Oneofthebestsubstancesusedtomakeopticalfibersisultra-purefusedsilica.Thesefibersaremoreexpensivethanregularglassfibers.Plasticfibersarenormallyusedforshort-distancelinkswherehigherlosses

aretolerable.Opticalfiberlinksareusedinalltypesofnetworks,LANandWAN.Thefrequencyrangeoffiberopticsisapproximately180THzto330THz.Therearetwotypesoffiberopticscables:multi-modefiberandsingle-modefiber. Ultra（名、形、副）超，极端Achieve/achievement(经过努力)实现、得到、完成Realize（从抽象到具体）实现、认识到Complete（完整地）完成Finish结束、完成Convert转变、转换Translate翻译、转化Change改变turnto变成generate形成、生成create创造form构成、形成ultra可以作为词素构成紫外线、超声波等，单独的意思是“过激分子、极端的（地）”；相关的有intra、inter等。Single-modefiberconsistsofthesamepartsasmulti-mode.Theouterjacketofsingle-modefiberisusuallyyellow.Themajordifferencebetweenmulti-modeandsingle-modefiberisthatsingle-modeallowsonlyonemodeoflighttopropagatethroughthesmaller,fiber-opticcore.Thesingle-modecoreiseighttotenµmindiameter.Nine-microncoresarethemostcommon.A9/125markingonthejacketofthesingle-modefiberindicatesthatthecorefiberhasadiameterof9micronsandthesurroundingcladdingis125micronsindiameter.Aninfraredlaserisusedasthelightsourceinsingle-modefiber.Therayoflightitgeneratesentersthecoreata90-degreeangle.Thedatacarryinglightraypulsesinsingle-modefiberareessentiallytransmittedinastraightlinerightdownthemiddleofthecore.Thisgreatlyincreasesboththespeedandthedistancethatdatacanbetransmitted.Single-modefiberiscapableofhigherbandwidthandgreatercablerundistancesthanmulti-modefiber.Single-modefibercancarryLANdataupto3km.Althoughthisdistanceisconsideredastandard,newertechnologieshaveincreasedthisdistance.Multi-modeisonlycapableofcarryingupto2km.Lasersandsingle-modefibersaremoreexpensivethanLEDsandmulti-modefibers.Becauseofthesecharacteristics,single-modefiberisoftenusedforinter-buildingconnectivity.μm/micon/micrometer/millimillimeter微米BecapableofBeableto

laser激光(LightAmplificationStimulatedEmissionRadiation)光放大受激发射辐射RadioRadiateRadiationRadiusLightrayscanonlyenterthecoreiftheirangleisinsidethenumericalapertureofthefiber.Oncetherayshaveenteredthecoreofthefiber,therearealimitednumberofopticalpathsthatalightraycanfollowthroughthefiber.Theseopticalpathsarecalledmodes.Ifthediameterofthecoreofthefiberislargeenoughsothattherearemanypathsthatlightcantakethroughthefiber,thefiberiscalled“multi-mode”fiber.Single-modefiberhasamuchsmallercorethatonlyallowslight