【正文】 ypes of line configuration ?Pointtopoint Line Configuration :A dedicated link can be used to connection two puters permanently. ?Multipoint line configuration:A shared link can be used to connection more than two munication devices 12 Multipoint Line Configuration 13 Figure :mesh topology ? mesh topology: Each node is connected by a dedicated link with other nodes 14 feature ? Each pair of devices is connected by a dedicated link ? This solution is not feasible for a large number of devices， because of ?n(n1)/2 transmission lines are required for interconnecting n devices in solution a ?The cost would be prohibitive ?Resources wasted 15 Figure : star topology ? star topology:each device is only connected by a dedicated link with central controller such as hub. ? Each pair of devices is not connected. 16 feature ? Some links are used by different pairs of devices. ? A work is anized so as to have different information flows share munication links. ? Solution b achieves savings in link length. ?N transmission lines are required for interconnecting n devices in solution b ? One of the main work design problems is to find efficient ways of sharing munication links. 17 Definition ? A munication work is a set of nodes that are interconnected to permit the exchange of information.（ 通信網(wǎng)絡(luò)是用來交換信息的互聯(lián)節(jié)點組） ? Nodes: ?Terminal entities:such as phone sets,puters,printers,file servers or video monitors ?Communication devices:switches,routers,repeaters(中繼器） ? Terminal nodes（ 終端節(jié)點） :generate or use information ? Communication nodes（ 通信節(jié)點） :transport information 18 Evolution of Communication Networks ? We examine the main steps in the evolution of the telephone and puter works ? 我們將介紹給用戶提供網(wǎng)絡(luò)服務(wù)的通信網(wǎng)絡(luò)發(fā)展的主要過程。 MUX DEMUX One link Three channel 24 Types of multiplexing ? TDM( TimeDivision Multiplexing) ? FDM( FrequencyDivision Multiplexing) ? CDM( CodeDivision Multiplexing) ? WDM( WaveDivision Multiplexing) 25 Multiplexing, Frequency Domain 26 Demultiplexing, Frequency Domain 27 TDM 28 CCS（公共信道信令） ? Common channel signaling transmits connection control information among telephone switching equipment. ? This control information permits efficient implementations of many services,such as call forwarding,credit card calls,and 800 numbers.（ 呼叫轉(zhuǎn)移、信用卡呼叫、 800免費電話） 29 Integration of Services ? Digital transmission and mon channel signaling form the basis of the ISDNs(綜合業(yè)務(wù)數(shù)字網(wǎng)） ? TDM(TimeDivision Multiplexing:時分多路復用） ? 2B channels:transmit voice or puter datadigital transmission 用于傳送用戶數(shù)據(jù)。 38 ? The transmission rate is 交換網(wǎng)絡(luò)中，連接以固定數(shù)據(jù)速率傳輸。其標準為 RS232C。 ? 兩個 DTE設(shè)備不需要互相協(xié)調(diào) ,但是每個 DTE設(shè)備必須與它所連接的 DCE設(shè)備協(xié)調(diào)工作。 55 Figure:A longdistance connection terminal Modem Modem Computer Telephone line A longdistance connection ? To implement a longdistance connection between a terminal and a puter,one can connect the terminal to a modem,the modem to a telephone line,and the other end of the line to another modem that is connected to the puter. 56 Summary: ? 通過調(diào)制解調(diào)器，可以實現(xiàn)兩個計算機之間的遠程通信，上圖是實現(xiàn)兩個計算機通過電話網(wǎng)進行通信的聯(lián)接框圖。即數(shù)據(jù)被當作不間斷的 0和 1比特流傳輸，而由接收方來將比特流分割成重建信息所需的一個個字節(jié)。 ? If the receiver is busy,the packet can store in some node and wait for a free ，在接收者“忙”時，網(wǎng)絡(luò)節(jié)點可先將信息存儲在中間某個節(jié)點等待鏈路的空閑。 78 ? If conditions(congestion,a link may fail) change in the work,successive packets that belong to the same munication between two puters may follow different paths in the works. ? 如果網(wǎng)絡(luò)的條件發(fā)生變化（擁塞、鏈路故障），在兩臺計算機之間屬于同一條通信的連續(xù)數(shù)據(jù)報可能沿著不同的路徑到達目的地。 87 Figure ? The puters of the ALOHA work transmit on the same radio channel whenever they have a packet to transmit. Multipleaccess works channel 88 ? When two or more puters try to transmit simultaneously,the information is garbled.(混淆） ? The puters transmit their packets,then check whether the transmissions were garbled。當通信量不大時，這種網(wǎng)絡(luò)比較有效，且控制簡單。 A,B,C按先后順序來到，則復接情況如圖 TDM 3:1 A1 A0 B1 B0 C1 C0 B1 C0 頭 B0 A1 頭 frame A0 頭 可見，對于可變速率的業(yè)務(wù)來說，顯然會降低信道利用率 101 異步 TDM ? 在異步 TDM中，各個信元 動態(tài) 地占用信道 頭 頭 頭 頭 信道 1 信道 5 信道 8 信道 2 圖：異步時分復接信道被占用情況 102 ATM ? A,B,C三個輸入經(jīng)異步 TDM復接后輸出，由于每條輸入的信元流在輸出信元流中所占的位置不象同步 TDM那樣，而是不固定的，所以稱“ 異步” A1 A0 B1 B0 C1 C0 TDM 3:1 C0 C1 B1 A1 B0 A0 103 Organization of the book ? Chapter 2:the main operating principles of works,provide a big picture of work ? chapter 3:Inter protocols ? chapter 4:LAN:Ether,token ring and FDDI ? chapter 5:ATM:protocols,classes of services,routing ? chapter 6:data