1、Chapter 4,Signals, Media, And Data Transmission,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chap4Part 1,Transmission of Information,Well-understood basics From physics Energy Electromagnetic wave propagation From mathematics Coding theory,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chap4Part 1,Transmi
2、ssion Media,贵间演钟四嘛嫩盗取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chap4Part 1,Transmission Media,Copper wire Need two wires Possibilities Twisted pair Coaxial cable Optical fiber Flexible Light “stays in” Air / space Used for electromagnetic transmission,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chap4Part 1,T
3、wisted pair,Two insulated copper wires are twisted around each other Twisted pairs often are bundled together and wrapped in a protective coating that allows the bundled cable to be buried Twisting minimizes electromagnetic interference between pairs Bandwidth up to 250 kHz for analog signals Digita
4、l signal data rates vary with distance 100 Mbps over a segment length of 100m 2400 bps for up to 10 miles,撤冀战伴敝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chap4Part 1,Terminology,Analog data take on continuous values in a given interval, e.g. audio (human speech) or video. Digital data take on discrete va
5、lues, e.g. text or integers. Signals are electromagnetic representations of data. Signaling is the physical propagation of the signal along a suitable medium. Transmission is the communication of data by the propagation and processing of signals. Bandwidth Maximum times per second the signal can cha
6、nge,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chap4Part 1,Terminology,Analog signal is a continuously varying electromagnetic wave.Used in early telephone systems.Analog signals had the drawback that they attenuate (weaken) over long distances. Needed amplifiers to boost the signals. However, ampli
7、fiers distort the signal and introduce noise. Digital signal is a sequence of binary voltage pulses (0s and 1s). Digital transmission avoids the noise problem by encoding the analog signal into digital form. The digitized version is then sent across the network.,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
8、与互联网英语chap4Part 1,Shielded twisted-pair cable (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chap4Part 1,UTP cable,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chap4Part 1,UTP Categories,Cat 3 up to 16MHz Voice grade found in most offices Twist length of 7.5 cm to 10 cm Cat 4 up to 20 MHz Cat 5 up t
9、o 100MHz Commonly pre-installed in new office buildings Twist length 0.6 cm to 0.85 cm,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chap4Part 1,UTP cable,The following are the types of cable connections used between internetwork devices: straight-through cable crossover cable,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
10、刊颜粒景哮廉值计算机网络与互联网英语chap4Part 1,straight-through cable,Use for the following cabling: Switch to router Switch to PC or server Hub to PC or server,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chap4Part 1,Crossover cable,Use for the following cabling: Switch to switch Switch to hub Hub to hub Router to ro
11、uter PC to PC Router to PC,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计算机网络与互联网英语chap4Part 1,UTP connector,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chap4Part 1,Coaxial cable,Bandwidth of about 500 Mbps More expensive than twisted pair transmits information baseband mode bandwidth devoted to a single stream o
12、f data broadband mode bandwidth is divided into ranges each range typically carries separate coded information allows the transmission of multiple data streams over the same cable simultaneously eg. Cable TV,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chap4Part 1,Table Categories of coaxial cables,Co
13、axial cable,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chap4Part 1,Optical fiber,Use optical signals instead of electrical signals Light sources : LED (Light Emitting Diode,发光二极管）/Laser Diode Optical Fibers Stepped Index Multimode Graded Index Multimode Single Mode Detector: Photoelectric(光电) Diodes
14、,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chap4Part 1,Total internal reflection,The following two conditions must be met for the light rays in a fiber to be reflected back into the fiber without any loss due to refraction(折射): The core of the optical fiber has to have a larger index of refraction
15、(n) than the material that surrounds it. The material that surrounds the core of the fiber is called the cladding. The angle of incidence (入射角) of the light ray is greater than the critical angle (临界值) for the core and its cladding.,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chap4Part 1,Total intern
16、al reflection,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chap4Part 1,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chap4Part 1,Optical Fiber - Transmission Characteristics,Act as wave guide for 1014 to 1015 Hz Portions of infrared and visible spectru
17、m Light Emitting Diode (LED) Cheaper Wider operating temp range Last longer Injection Laser Diode (ILD) More efficient Greater data rate Wavelength Division Multiplexing,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chap4Part 1,Single-mode fiber,Single-mode fiber consists of the same parts as multimode
18、 The outer jacket of single-mode fiber is usually yellow Single-mode allows only one mode of light to propagate through the smaller, fiber-optic core An infrared(红外) laser is used as the light source in single-mode fiber has greater both the speed and the distance than multi-mode fiber. single-mode
19、fiber is often used for inter-building connectivity,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chap4Part 1,Multimode fiber,The part of an optical fiber through which light rays travel is called the core of the fiber These optical paths are called modes. If the diameter of the core of the fiber is la
20、rge enough so that there are many paths that light can take through the fiber, the fiber is called “multimode” fiber. Single-mode fiber has a much smaller core that only allows light rays to travel along one mode inside the fiber,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chap4Part 1,Comparative of
21、two fiber,Multimode fiber,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chap4Part 1,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chap4Part 1,fiber-optic component,Usually, five parts make up each fiber-optic cable: core the cladding a buffer a strength material an outer jacket,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
22、笼摹泛童迹计算机网络与互联网英语chap4Part 1,fiber-optic component,A core is typically glass made from a combination of silicon dioxide (silica) and other elements Cladding is also made of silica but with a lower index of refraction than the core buffer material is usually plastic , helps shield the core and claddin
23、g from damage The strength material surrounds the buffer, preventing the fiber cable from being stretched when installers pull it The outer jacket surrounds the cable to protect the fiber against abrasion(磨损), solvents(溶解), and other contaminants (污染物) The color of the outer jacket of multimode fibe
24、r is usually orange,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chap4Part 1,transmitter and receiver,Each of these light sources can be lighted and darkened very quickly to send data (1s and 0s),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chap4Part 1,Connectors,multimode fiber is the Subscriber Connec
25、tor (SC connector). single-mode fiber is the Straight Tip (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chap4Part 1,Figure Wireless transmission waves,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chap4Part 1,Electromagnetic Spectrum,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网英语chap4Part 1,Fo
26、rms of Energy Used To Transmit Data,Electric current Audible sounds Omnidirectional electromagnetic waves Radio Frequency (RF) Infrared Directional electromagnetic waves Point-to-point satellite channel Limited broadcast (spot beam) Microwave Laser beam,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cha
27、p4Part 1,Figure Electromagnetic spectrum for wireless communication,Figure Propagation methods,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chap4Part 1,Types of Satellites,Geosynchronous Earth Orbit (GEO),Keplers third law : P2=K D3 P : time to rotate around another planetary (period) D : distance bet
28、ween satellite and the planets center K : constant depending on gravitational forces Geosynchronous orbit P= 24-hour D=(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chap4Part 1,Types of Satellites,Low Earth Orbit (LEO) Array needed,伯塌辖哆金辟福攒库烤催迟屁熟涣悍次厂永称吹仟屉舅基们旭灯博库擅峻计算机网络与互联网英语chap4Pa
29、rt 1,(a) Relaying in space. (b) Relaying on the ground.,Globalstar,庆面逐挺三隔昌娱痰穆茵梁洁办掌午奄啮架氖飞许史涧汾着癣靛镜亢样创计算机网络与互联网英语chap4Part 1,Terrestrial Microwave,Parabolic dish(抛物柱面反射器) Focused beam(聚焦光束) Line of sight(瞄准线) Long haul(持久) telecommunications Higher frequencies give higher data rates,杆碧慢篓台度壁全靳壤缆燥码农苟雀稼谴夫
30、却吊涕唁绥腔蒸介向糯总撩盐计算机网络与互联网英语chap4Part 1,Satellite Microwave,Satellite is relay station Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency Requires geo-stationary orbit Height of 35,784km Television Long distance telephone Private business networks,瞒瓷扒酝狡费虱足措名讳栽焰漱淫侮驳鉴裙筒咎迄枪盖阜戚因风罢然枉桥计算机网络与互联网英语chap4Part 1,Infrared,Modulate no coherent infrared light Line of sight (or reflection) Blocked by walls e.g. TV remote control, IRD port,惹率薛叼簿秋饵终殴宪楷猿闭驭仕了野及虚漂翠钦郝牵钎挝迭靶墓篮胆汾计算机网络与互联网英语chap4Part 1,
