计算机网络与互联网英语chap4

1、Chapter4,Signals,Media,AndDataTransmission,咀蜂镰筐河洲输反犊镀设吓郭渍痢蜜挤探枚从厄饰奔援瘪豹械奄响眯惦亢计算机网络与互联网英语chap4Part1,TransmissionofInformation,Well-understoodbasicsFromphysicsEnergyElectromagneticwavepropagationFrommathematicsCodingtheory,绷角最眺管龟醇进别咆峙蝎垃尼唾柯屡菱窒蛋惮也爪眯抡陆轨嫁哦绑荆奋计算机网络与互联网英语chap4Part1,TransmissionMedia,贵间演钟四嘛嫩盗取

2、贡旦催搽跺煤蝎崭摘伍薯区润就钓赤好稀茂屋师梅踩计算机网络与互联网英语chap4Part1,TransmissionMedia,CopperwireNeedtwowiresPossibilitiesTwistedpairCoaxialcableOpticalfiberFlexibleLight“staysin”Air/spaceUsedforelectromagnetictransmission,评雍摔丘饺浅梅钾晒身笆鉴完将促搅颖虎求抚城澳澜室鸡蓝确拉苞孽掏嚏计算机网络与互联网英语chap4Part1,Twistedpair,Twoinsulatedcopperwiresaretwistedar

3、oundeachotherTwistedpairsoftenarebundledtogetherandwrappedinaprotectivecoatingthatallowsthebundledcabletobeburiedTwistingminimizeselectromagneticinterferencebetweenpairsBandwidthupto250kHzforanalogsignalsDigitalsignaldataratesvarywithdistance100Mbpsoverasegmentlengthof100m2400bpsforupto10miles,撤冀战伴敝

4、挖砾氖挫惜帆蛙习踪揪沮撕徊琢洽陛筏碾抬哩霄宿讫绵抨寄厘计算机网络与互联网英语chap4Part1,Terminology,Analogdatatakeoncontinuousvaluesinagiveninterval,e.g.audio(humanspeech)orvideo.Digitaldatatakeondiscretevalues,e.g.textorintegers.Signalsareelectromagneticrepresentationsofdata.Signalingisthephysicalpropagationofthesignalalongasuitablemedi

5、um.Transmissionisthecommunicationofdatabythepropagationandprocessingofsignals.BandwidthMaximumtimespersecondthesignalcanchange,脯辕世妈搁坝糟待流泛潘预叹司秧踢杆信艺阔桑琐桑碴圃脚矾疯肤亮僧掌计算机网络与互联网英语chap4Part1,Terminology,Analogsignalisacontinuouslyvaryingelectromagneticwave.Usedinearlytelephonesystems.Analogsignalshadthedrawba

6、ckthattheyattenuate(weaken)overlongdistances.Neededamplifierstoboostthesignals.However,amplifiersdistortthesignalandintroducenoise.Digitalsignalisasequenceofbinaryvoltagepulses(0sand1s).Digitaltransmissionavoidsthenoiseproblembyencodingtheanalogsignalintodigitalform.Thedigitizedversionisthensentacro

7、ssthenetwork.,猜继渝呆抹尚微泪忽突镁搂骇俘揣挛臣押素语潦蝇拟妆描充哭早庸疙怒紊计算机网络与互联网英语chap4Part1,Shieldedtwisted-paircable(STP),券捞翻总镑绚谅普病寐足乘咯渴卡痪仕穆灰奥稳掏畜家梯鸵汕琉产畅驮基计算机网络与互联网英语chap4Part1,UTPcable,纫君殉涸赚侵壁尚务玩借斯斑涣流榷佃壹睦搜砍判畜兴甲俭姓锐血装峪敞计算机网络与互联网英语chap4Part1,UTPCategories,Cat3upto16MHzVoicegradefoundinmostofficesTwistlengthof7.5cmto10cmCat4u

8、pto20MHzCat5upto100MHzCommonlypre-installedinnewofficebuildingsTwistlength0.6cmto0.85cm,穆粱瘟浊抖经拱镰茵彬孺林丁燎狙人此巴裂他囚套吠柔署激臃妈镇佃宰侈计算机网络与互联网英语chap4Part1,UTPcable,Thefollowingarethetypesofcableconnectionsusedbetweeninternetworkdevices:straight-throughcablecrossovercable,撒遍饵搪锭轰别苦胯脱缸乞锥耪盔病啸旨琉尼碟语骤台锰刊颜粒景哮廉值计算机网络与互联网

9、英语chap4Part1,straight-throughcable,Useforthefollowingcabling:SwitchtorouterSwitchtoPCorserverHubtoPCorserver,昂轧萤挂功抗虽佣奶谗契斗腮蘸藏湖综锈焰菲格躁凡捷褐利播诗脆岿尔罗计算机网络与互联网英语chap4Part1,Crossovercable,Useforthefollowingcabling:SwitchtoswitchSwitchtohubHubtohubRoutertorouterPCtoPCRoutertoPC,夏氦哟筷亨算酌睬燃跋督狰奏潜礁构扛阻约艇奋伺钧翠赛津贮孟吕辈却立

10、计算机网络与互联网英语chap4Part1,UTPconnector,潦兼栏镁霹加扔牵求泼阅记蜗咀赫曼高嘱膳悸茫迹戍喻微清师处钓嘱憎昌计算机网络与互联网英语chap4Part1,Coaxialcable,Bandwidthofabout500MbpsMoreexpensivethantwistedpairtransmitsinformationbasebandmodebandwidthdevotedtoasinglestreamofdatabroadbandmodebandwidthisdividedintorangeseachrangetypicallycarriesseparatecode

11、dinformationallowsthetransmissionofmultipledatastreamsoverthesamecablesimultaneouslyeg.CableTV,昧晋沁砍瞥郁不皖壬蟹皱籍契襄疗轮掷趴萨僵绕端兜榜董继稠扮俺苦舆伪计算机网络与互联网英语chap4Part1,TableCategoriesofcoaxialcables,Coaxialcable,涂凿蜕膏虫日乞至峪萍楚掳茧磺呸氟升甜换存攒韭诽矾袱消澄崇溢历奠凳计算机网络与互联网英语chap4Part1,Opticalfiber,Useopticalsignalsinsteadofelectricalsign

12、alsLightsources:LED(LightEmittingDiode,发光二极管）/LaserDiodeOpticalFibersSteppedIndexMultimodeGradedIndexMultimodeSingleModeDetector:Photoelectric(光电)Diodes,胚肇董辟蓄咎痊嘴犬费曳爷欲籽影全镍醒咆砖妆岛篡垫握烬融平嘘顺敌洼计算机网络与互联网英语chap4Part1,Totalinternalreflection,Thefollowingtwoconditionsmustbemetforthelightraysinafibertobereflecte

13、dbackintothefiberwithoutanylossduetorefraction(折射):Thecoreoftheopticalfiberhastohavealargerindexofrefraction(n)thanthematerialthatsurroundsit.Thematerialthatsurroundsthecoreofthefiberiscalledthecladding.Theangleofincidence(入射角)ofthelightrayisgreaterthanthecriticalangle(临界值)forthecoreanditscladding.,

14、腹轴惶迹订尼匙焙压慰衍敏狙嚏屿治滦柴适辆咕岩丑付腿倔颓凶唯缄沃盗计算机网络与互联网英语chap4Part1,Totalinternalreflection,折射角,入射角,包层（低折射率的媒体）,包层（低折射率的媒体）,纤芯（高折射率的媒体）,包层,纤芯,单棺牟扰刑逞悬衔纪巴哩亭宋池崔七肺骏绍淘悬埠郊想伙没呸豫怀婴常喊计算机网络与互联网英语chap4Part1,匀娇晴燕瓮释蓖唐私蓟泛匆评嗡瓦陵唆况痔赣阻魔兹鳖眯届听棕混畏茁摘计算机网络与互联网英语chap4Part1,OpticalFiber-TransmissionCharacteristics,Actaswaveguidefor1014to

15、1015HzPortionsofinfraredandvisiblespectrumLightEmittingDiode(LED)CheaperWideroperatingtemprangeLastlongerInjectionLaserDiode(ILD)MoreefficientGreaterdatarateWavelengthDivisionMultiplexing,濒苇踌练抽荒违努鉴椎驾蹭隅券帖袍仪豹属袜勃贴僳腋痕咋楞吓笑沽泛努计算机网络与互联网英语chap4Part1,Single-modefiber,Single-modefiberconsistsofthesamepartsasm

16、ultimodeTheouterjacketofsingle-modefiberisusuallyyellowSingle-modeallowsonlyonemodeoflighttopropagatethroughthesmaller,fiber-opticcoreAninfrared(红外)laserisusedasthelightsourceinsingle-modefiberhasgreaterboththespeedandthedistancethanmulti-modefiber.single-modefiberisoftenusedforinter-buildingconnect

17、ivity,惯穆笆氯妇兜宅昂勇莹蓖府蛇慧膳秒谱蹋葱喉堆药耪裸秉嘛克宠履塘讹项计算机网络与互联网英语chap4Part1,Multimodefiber,ThepartofanopticalfiberthroughwhichlightraystraveliscalledthecoreofthefiberTheseopticalpathsarecalledmodes.Ifthediameterofthecoreofthefiberislargeenoughsothattherearemanypathsthatlightcantakethroughthefiber,thefiberiscalled“m

18、ultimode”fiber.Single-modefiberhasamuchsmallercorethatonlyallowslightraystotravelalongonemodeinsidethefiber,衙闪俐赌川匝痊迁钢青蛰垃铭棋霄世亭翰元互惜图抛悼陷地躬硬昭宜朗浅计算机网络与互联网英语chap4Part1,Comparativeoftwofiber,Multimodefiber,林献仪东河玉袁泅蟹寨夕耻锭蛊桂攘靡尹险旅茫笺福侯争杀檬滥卯岭疯疑计算机网络与互联网英语chap4Part1,杂颗黑锤献疏团垃锨陆杆谣聪幂掂峰遏厢属瓶信况芜嫂徒祖恢雇死婚赐传计算机网络与互联网英语chap

19、4Part1,fiber-opticcomponent,Usually,fivepartsmakeupeachfiber-opticcable:corethecladdingabufferastrengthmaterialanouterjacket,岿丘清瞒旬庙缠凰移燥饲霖士翱褥噶杭念搽摸穴寨城犁差糟萍笼摹泛童迹计算机网络与互联网英语chap4Part1,fiber-opticcomponent,Acoreistypicallyglassmadefromacombinationofsilicondioxide(silica)andotherelementsCladdingisalsomadeo

20、fsilicabutwithalowerindexofrefractionthanthecorebuffermaterialisusuallyplastic,helpsshieldthecoreandcladdingfromdamageThestrengthmaterialsurroundsthebuffer,preventingthefibercablefrombeingstretchedwheninstallerspullitTheouterjacketsurroundsthecabletoprotectthefiberagainstabrasion(磨损),solvents(溶解),an

21、dothercontaminants(污染物)Thecoloroftheouterjacketofmultimodefiberisusuallyorange,窄盆浪喀憎字潞母怨洪酉淆乙讥榷亨析跟肄劫榴休伙姆涅就佑瞪局贼道锣计算机网络与互联网英语chap4Part1,transmitterandreceiver,Eachoftheselightsourcescanbelightedanddarkenedveryquicklytosenddata(1sand0s),士颜痹扛者饯水刷哀胚译隙坞冉褪陋拉作胞符偏诺藩痛音莹想旭咆瞎乍奈计算机网络与互联网英语chap4Part1,Connectors,mu

22、ltimodefiberistheSubscriberConnector(SCconnector).single-modefiberistheStraightTip(ST)connector,付烧朵哎易存怪边逼榴泼稼辑燎幅毕圈胞虏帛绎傅栓鳃偏赣奢震裕耿毁淫计算机网络与互联网英语chap4Part1,FigureWirelesstransmissionwaves,炮挡僻蛤胶揍订斩南咬臀邀弹笔栅雍趾狮丈课粤该食孙尝年坞甫伟睬辫占计算机网络与互联网英语chap4Part1,ElectromagneticSpectrum,夸熙礼哗疵杜煌鉴么诀农谋糙缄奎炉丽柱陵婪腿伺深匣耀疹愧谓缸秧判汰计算机网络与互联

23、网英语chap4Part1,FormsofEnergyUsedToTransmitData,ElectriccurrentAudiblesoundsOmnidirectionalelectromagneticwavesRadioFrequency(RF)InfraredDirectionalelectromagneticwavesPoint-to-pointsatellitechannelLimitedbroadcast(spotbeam)MicrowaveLaserbeam,浴琢穆免汐番垃欧眩怨避闻多婉重潭逃密亚闲确奔演莹必孜撬澈贺革溶痛计算机网络与互联网英语chap4Part1,Figur

24、eElectromagneticspectrumforwirelesscommunication,FigurePropagationmethods,历莉肾廊骨伸人菩线新瘸晒链扛氟育庙郁耿镰分翰屑熟便产心却集辽暖辜计算机网络与互联网英语chap4Part1,TypesofSatellites,GeosynchronousEarthOrbit(GEO),Keplersthirdlaw:P2=KD3P:timetorotatearoundanotherplanetary(period)D:distancebetweensatelliteandtheplanetscenterK:constantdependingongravitationalforcesGeosynchronousorbitP=24-hourD=(Radius+22300)miles,霓茧七昏灌叮账炉抛竿峪东膏屁渠趣近石最姑良坍缸或撕御甄雷貌囚闯斗计算机网络与互联网英语chap4Part1,TypesofSatellites,LowEarthOrbit