DataandComputerCommunications實(shí)用教案

1、為充分利用通信干線的傳輸容量為充分利用通信干線的傳輸容量(rngling)(rngling)，常采用多路復(fù)用技術(shù)。，常采用多路復(fù)用技術(shù)。多路器多路器( (復(fù)用器復(fù)用器) )組合組合N N路輸入線路上的數(shù)路輸入線路上的數(shù)據(jù)據(jù), ,通過一條高容量通過一條高容量(rngling)(rngling)的數(shù)的數(shù)據(jù)鏈路傳輸；分路器接收到復(fù)用的數(shù)據(jù)據(jù)鏈路傳輸；分路器接收到復(fù)用的數(shù)據(jù)流流, ,按通道分離按通道分離( (分路分路) )這些數(shù)據(jù)這些數(shù)據(jù), ,把它們把它們送到適當(dāng)?shù)妮敵鼍€路上。送到適當(dāng)?shù)妮敵鼍€路上。多路復(fù)用第1頁/共52頁第一頁，共53頁。幾種類型幾種類型(lixng)(lixng)的多路復(fù)的多路復(fù)用

2、技術(shù)用技術(shù) 頻分多路復(fù)用(FDM) 在無線電和電視機(jī)技術(shù)中廣為使用； 同步時(shí)分多路復(fù)用(TDM) 時(shí)分多路復(fù)用的特殊情況,常被稱為TDM,普遍用于多路復(fù)用數(shù)字語音流的傳輸； 統(tǒng)計(jì)TDM 通過在多路器上增加一些復(fù)雜處理提高同步TDM的效率,各種熟悉(shx)的名稱包括：統(tǒng)計(jì)TDM、異步TDM、智能TDM，統(tǒng)計(jì)TDM的名稱指出了它的主要特性。第2頁/共52頁第二頁，共53頁。頻分多路復(fù)用頻分多路復(fù)用子載波fsc1m1(t)Ssc1(t)子載波fsc2m2(t)Ssc2(t)子載波fscNmN(t)SscN(t)發(fā)送器fcmc(t)s(t)=FDM:NoImagefsc1Bsc1fsc2Bsc2fs

3、cNBscNBf| Mc(f) |0(a) 發(fā)送器(b) 復(fù)合(fh)信號(hào)的譜(正f)第3頁/共52頁第三頁，共53頁。頻分多路復(fù)用頻分多路復(fù)用帶通濾波器,fsc1接收器帶通濾波器,fsc2帶通濾波器,fscN解調(diào)器,fsc1解調(diào)器,fsc2解調(diào)器,fscNm2(t)m1(t)mN (t): :s(t)(c) 接收器第4頁/共52頁第四頁，共53頁。頻分復(fù)用頻分復(fù)用(f yn(f yn) )CH2CH1CH3原始帶寬原始帶寬CH1CH2CH3頻分后帶寬頻分后帶寬MUXCH1 CH2 CH3帶寬復(fù)用帶寬復(fù)用f第5頁/共52頁第五頁，共53頁。波分復(fù)用波分復(fù)用(f yn(f yn) )：FDMFD

4、M的變形的變形F2F1F3 光譜光譜F1F2F3共享光纖的光譜共享光纖的光譜光纖光纖2光纖光纖3光纖光纖1共享光纖共享光纖 采用無源設(shè)備，更可靠采用無源設(shè)備，更可靠棱柱棱柱/衍射光柵衍射光柵第6頁/共52頁第六頁，共53頁。時(shí)分復(fù)用時(shí)分復(fù)用A2A1A3原始信號(hào)D2D1D3數(shù)字化信號(hào)MUX復(fù)用后數(shù)據(jù)復(fù)用后數(shù)據(jù)時(shí)隙時(shí)隙1234D3D2D1第7頁/共52頁第七頁，共53頁。復(fù)用復(fù)用(f yn(f yn) )：共享使用公共信道：共享使用公共信道 z DEMUX復(fù)用器復(fù)用器解復(fù)用器解復(fù)用器共享信道共享信道(xn do)MUX第8頁/共52頁第八頁，共53頁。Multiplexing第9頁/共52頁第九頁

5、，共53頁。8.1Frequency Division Multiplexing(1) FDM頻分復(fù)用 Useful bandwidth of medium exceeds required bandwidth of channel 在傳輸媒體的有效帶寬超出信道需要的帶寬時(shí),就可以使用FDM Each signal is modulated to a different carrier frequency 每一個(gè)(y )信號(hào)調(diào)制到不同的載波頻率第10頁/共52頁第十頁，共53頁。Frequency Division Multiplexing(2) Carrier frequencies sep

6、arated so signals do not overlap (guard bands) 載波頻率要相互隔離使信號(hào)(xnho)不重疊(防護(hù)頻帶) e.g. broadcast radio Channel allocated even if no data第11頁/共52頁第十一頁，共53頁。Frequency Division MultiplexingDiagram第12頁/共52頁第十二頁，共53頁。FDM System第13頁/共52頁第十三頁，共53頁。FDM of Three Voiceband Signals第14頁/共52頁第十四頁，共53頁。Analog Carrier Sy

7、stems(1) AT&T (USA)美國電話電報(bào)公司 Hierarchy of FDM schemes Group(基群) 12 voice channels (4kHz each) = 48kHz Range 60kHz to 108kHz第15頁/共52頁第十五頁，共53頁。Analog Carrier Systems(2) Supergroup(超群(choqn) 60 channel FDM of 5 group signals on carriers between 420kHz and 612 kHz Mastergroup(主群) 10 supergroups第16頁/共52頁

8、第十六頁，共53頁。8.2 Synchronous Time Division Multiplexing Data rate of medium exceeds data rate of digital signal to be transmitted Multiple digital signals interleaved in time May be at bit level of blocks Time slots pre-assigned to sources and fixed Time slots allocated even if no data Time slots do no

9、t have to be evenly distributed amongst sources(不必在數(shù)據(jù)源間均勻分配(fnpi)時(shí)隙)第17頁/共52頁第十七頁，共53頁。Time Division Multiplexing第18頁/共52頁第十八頁，共53頁。TDM System第19頁/共52頁第十九頁，共53頁。TDM Link Control No headers and tailers(傳輸數(shù)據(jù)流無首尾部(wi b) Data link control protocols not needed Flow control Data rate of multiplexed line i

10、s fixed If one channel receiver can not receive data, the others must carry on The corresponding source must be quenched This leaves empty slots Error control Errors are detected and handled by individual channel systems第20頁/共52頁第二十頁，共53頁。Data Link Control on TDM第21頁/共52頁第二十一頁，共53頁。Framing No flag o

11、r SYNC characters bracketing TDM frames(無標(biāo)志(biozh)或SYNC對TDM定界) Must provide synchronizing mechanism Added digit framing(增加數(shù)字組幀) One control bit added to each TDM frame Looks like another channel - “control channel” Identifiable bit pattern used on control channel e.g. alternating 01010101unlikely on

12、 a data channel Can compare incoming bit patterns on each channel with sync pattern第22頁/共52頁第二十二頁，共53頁。Added digit framing(增加增加(zngji)數(shù)字組幀數(shù)字組幀) One control bit added to each TDM frame Looks like another channel - “control channel” 每一幀附加一控制位,看起來像另一個(gè)信道-控制信道 Identifiable bit pattern used on control cha

13、nnel 控制信道使用(shyng)可標(biāo)示位模式 e.g. alternating 01010101unlikely on a data channel 如數(shù)據(jù)信道不太可能的交替位模式01010101 Can compare incoming bit patterns on each channel with sync pattern第23頁/共52頁第二十三頁，共53頁。Pulse Stuffing(脈沖脈沖(michng)填充填充) Problem - Synchronizing various data sources Clocks in different sources drifti

14、ng Data rates from different sources not related by simple rational number Solution - Pulse Stuffing Outgoing data rate (excluding framing bits) higher than sum of incoming rates Stuff extra dummy bits or pulses into each incoming signal until it matches local clock Stuffed pulses inserted at fixed

15、locations in frame and removed at demultiplexer第24頁/共52頁第二十四頁，共53頁。Solution - Pulse Stuffing Outgoing data rate (excluding framing bits) higher than sum of incoming rates 輸出數(shù)據(jù)速率(不含幀定位比特)高于進(jìn)入數(shù)據(jù)速率和 Stuff extra dummy bits or pulses into each incoming signal until it matches local clock 對每一個(gè)輸入填充額外空比特或脈沖

16、直到(zhdo)匹配本地時(shí)鐘 Stuffed pulses inserted at fixed locations in frame and removed at demultiplexer 填充脈沖被插入幀中固定位置使分用器能刪除之第25頁/共52頁第二十五頁，共53頁。TDM of Analog and Digital Sources第26頁/共52頁第二十六頁，共53頁。Digital Carrier Systems Hierarchy of TDM USA/Canada/Japan use one system ITU-T use a similar (but different) s

17、ystem US system based on DS-1 format Multiplexes 24 channels Each frame has 8 bits per channel plus one framing bit 193 bits per frame第27頁/共52頁第二十七頁，共53頁。Digital Carrier Systems (2) For voice each channel contains one word of digitized data (PCM, 8000 samples per sec) Data rate 8000 x193 = 1.544Mbps

18、 Five out of six frames have 8 bit PCM samples Sixth frame is 7 bit PCM word plus signaling bit Signaling bits form stream for each channel containing control and routing info Same format for digital data 23 channels of data 7 bits per frame plus indicator bit for data or systems control 24th channe

19、l is sync第28頁/共52頁第二十八頁，共53頁。Mixed Data DS-1 can carry mixed voice and data signals 24 channels used No sync byte Can also interleave DS-1 channels Ds-2 is four DS-1 giving 6.312Mbps第29頁/共52頁第二十九頁，共53頁。ISDN User Network Interface ISDN allows multiplexing of devices over single ISDN line Two interfac

20、es Basic ISDN Interface Primary ISDN Interface第30頁/共52頁第三十頁，共53頁。Basic ISDN Interface (1) Digital data exchanged between subscriber and NTE - Full Duplex Separate physical line for each direction Pseudoternary coding scheme 1=no voltage, 0=positive or negative 750mV +/-10% Data rate 192kbps Basic ac

21、cess is two 64kbps B channels and one 16kbps D channel This gives 144kbps multiplexed over 192kbps Remaining capacity used for framing and sync第31頁/共52頁第三十一頁，共53頁。Basic ISDN Interface (2) B channel is basic iser channel Data PCM voice Separate logical 64kbps connections o different destinations D ch

22、annel used for control or data LAPD frames Each frame 48 bits long One frame every 250s第32頁/共52頁第三十二頁，共53頁。Frame Structure第33頁/共52頁第三十三頁，共53頁。Primary ISDN Point to point Typically supporting PBX 1.544Mbps Based on US DS-1 Used on T1 services 23 B plus one D channel 2.048Mbps Based on European standa

23、rds 30 B plus one D channel Line coding is AMI usingHDB3第34頁/共52頁第三十四頁，共53頁。Primary ISDN Frame Formats第35頁/共52頁第三十五頁，共53頁。Sonet/SDH Synchronous Optical Network (ANSI) Synchronous Digital Hierarchy (ITU-T) Compatible Signal Hierarchy Synchronous Transport Signal level 1 (STS-1) or Optical Carrier lev

24、el 1 (OC-1) 51.84Mbps Carry DS-3 or group of lower rate signals (DS1 DS1C DS2) plus ITU-T rates (e.g. 2.048Mbps) Multiple STS-1 combined into STS-N signal ITU-T lowest rate is 155.52Mbps (STM-1)第36頁/共52頁第三十六頁，共53頁。第37頁/共52頁第三十七頁，共53頁。SONETSDH比特率 (Mbps)STS-1/OC-1 51.84STS-3/OC-3 STM-1 155.52STS-9/OC-

25、9 STM-3 466.56STS-12/OC-12 STM-4 622.08STS-18/OC-18 STM-6 933.12STS-24/OC-24 STM-8 1244.16STS-36/OC-36 STM-12 1866.24STS-48/OC-48 STM-16 2488.32STS = Synchronous Transport Signal 同步傳輸信號(hào)(xnho)OC = Optical Carrier 光載波STM = Synchronous Transport Module 同步傳輸模塊第38頁/共52頁第三十八頁，共53頁。SONET 系統(tǒng)(xtng)sectionsec

26、tionsectionsectionlinelinepath復(fù)用器復(fù)用器中繼器中繼器中繼器中繼器復(fù)用器復(fù)用器復(fù)用器復(fù)用器Section： 段，任意段，任意(rny)兩個(gè)相鄰設(shè)備之間的光纖兩個(gè)相鄰設(shè)備之間的光纖line: 線路，線路， 兩個(gè)復(fù)用器之間兩個(gè)復(fù)用器之間 path: 通道，源站和目的站之間（端到端）通道，源站和目的站之間（端到端）第39頁/共52頁第三十九頁，共53頁。SONET Frame Format第40頁/共52頁第四十頁，共53頁。SONET STS-1 Overhead Octets第41頁/共52頁第四十一頁，共53頁。8.3 Statistical TDM In Syn

27、chronous TDM many slots are wasted Statistical TDM allocates time slots dynamically based on demand Multiplexer scans input lines and collects data until frame full Data rate on line lower than aggregate rates of input lines第42頁/共52頁第四十二頁，共53頁。Statistical TDM Frame Formats第43頁/共52頁第四十三頁，共53頁。Perform

28、ance Output data rate less than aggregate input rates May cause problems during peak periods Buffer inputs Keep buffer size to minimum to reduce delay第44頁/共52頁第四十四頁，共53頁。Buffer Size and Delay第45頁/共52頁第四十五頁，共53頁。8.4 Asymmetrical Digital Subscriber Line ADSL Link between subscriber and network Local loop Uses currently installed twisted pair cable Can carry broader spectrum 1 MHz or more第46頁/共52頁第四十六頁，共53頁。ADSL Design Asymmetric Greater capacity do