1基础(双语08版).ppt

1、计算机网络,中国海洋大学 计算机专业本科生 专业课,Brief introduction 本课程简介 Teaching evaluation excellence award of OUC in 2002 02年获得校级教学评估优秀奖 Best curricula of College of Information Science in 2003 03年获得信息学院院精品课程 Best curricula of OUC in 2004 04年获得中国海洋大学校级精品课程 Best curricula of ShanDong province in 2005 05年获得山东省省级精品课程 Sam

2、ple curricula of College of Information Science in 2006 06年确定为信息学院示范课程,Teacher introduction 主讲教师简介 Name: Tang Ruichun 姓名：唐瑞春 Ph.D. degree 理学博士 Position: associate professor, master tutor 职称：副教授，硕士生导师 Major in: network and its application 主要研究方向：网络及其应用技术 Please Contact me TelephoneOffice

3、: room 405,south building, college of information science and engineering 办公地点：信息学院南楼 B405室 e-mail: ,你眼中的网络是什么？ 本课程内容介绍,1 Foundation（基础）,PROBLEM：Building a Network （建造一个网络） Requirements, Cost-Effective Resource Sharing, Support for Common Services, Performance,1.1 Requirements(需求),1.1.1 Connectivity

4、(连通性） Links,Nodes 链路、结点 At the lowest level ,a network can consist of two or more computers directly connected by some physical medium ,such as a coaxial cable or an optical fiber .We call such a physical medium a link ,and we often refer to the computers it connects as nodes. 在最低层，网络可以由两台或更多的计算机通过某

5、种物理介质（如同轴电缆或光纤）直接相连。我们称这样的物理介质为链路，并称被连接的计算机为结点。,Physical links are sometimes limited to a pair of nodes (such a link is said to be point to point) ,while in other cases ,more than two nodes may share a single physical link (such a link is said to be multiple-access) 点到点的链路:限于一对结点的物理链路 多路访问的链路：可以有多个结

6、点共享一条物理链路,a) point-to-point(点到点)b) multiple-access(多路访问)Direct links（直接链路）,Work Station,Work Station,Work Station,Work Station,Work Station,Work Station,Switched network: each node is attached to one or more point-to-point links. Those nodes that are attached to at least two links as switched node.

7、Those nodes forwards data received on one link out on another. 交换网：每个结点都连到一条或多条点到点链路上，连接至少两条链路的结点作为交换节点，它负责将从一条链路收到的数据转发到另一条链路上。,There are two types of Switched network: 交换方式主要有两种： 1、circuit-switched: It is most notably employed by the telephone system. 电路交换：主要用于电话系统 2、packet-switched: It is used fo

8、r the overwhelming majority of computer networks. The important feature of packet-switched networks is that the nodes in such a network send discrete blocks of data to each other. Such as file piece of email or an image. we call each block of data either a packet or a message use a strategy called s

9、tore-and-forward. 分组交换：多用于计算机网络，其主要特点是网络中的结点彼此间发送离散的数据块，如一个文件、一个电子邮件或一幅图像。我们称每个数据块为一个分组或一条消息。使用存储转发的策略。,P1 P2 P3 P4,数据传送,报文,连接建立,连接释放,P1 P2 P3 P4,P1 P2 P3 P4,circuit-switched 电路交换,packet-switched 分组交换,Switched network 交换网,交换机 switch,主机 host,Switch: function is to store and forward packets 交换机：功能是存储和

10、转发分组 Host: supporting user and run application programs. 主机：任务是支持用户并运行应用程序,1.1.2 Cost-Effective Resource Sharing 成本效益高的资源共享,Frequency- Division Multiplexing: FDM transmit each flow over the physical link at a different frequency. 频分多路复用,FDM-将每个流以不同频率发向物理链路 Multiplexing multiple logical flows over a

11、single physical link 在一条物理链路上复用多个逻辑流,L1,L2,L3,R1,R3,R2,Switch1 (交换机1 ),Switch2 ( 交换机2 ),Multiplexing: system resource is shared among multiple users. 多路复用：系统资源可以被多个用户共享 Synchronous Time-Division Multiplexing: STDM divide time into equal-sized quanta and, in round-robin fashion, give each flow a chan

12、ce its data over physical link, for example during time quantum 1,data from the first flow is transmitted; during time quantum 2,data from the second flow is transmitted; and so on. 同步时分多路复用（STDM）：将时间划分为相等大小的份额，按轮转方式，使每个流都有机会将数据发送到物理链路上，例如：在时间片1中，发第一个流的数据；时间片2中，发第二个流的数据；等等。,1.1.3 Support for Common

13、Services 支持共同的服务,1.Identifying common communication patterns File access program like FTP (File Transfer Protocol) or NFS (Network File System), the communication component of remote file access is characterized by a pair of processes, one that requests that a file be read or written and second proc

14、ess that honors this request. The process the requests access to the file is called the client, and the process that supports access to the file is called server. 1.识别共同的通信模式 文件访问程序如FTP（文件传输协议）或NFS（网络文件系统），远程文件访问的通信部分可由一对进程来表示，第一个进程请求读/写文件，第二个进程响应这个请求。请求访问文件的进程叫客户机（client），支持访问文件的进程叫服务器（server）。,2.

15、Reliability 可靠性 There are three general classes of failure 故障通常有三类： A. Bit error: A single bits are corrupted or burst error-several consecutive bits are corrupted. Because of lightning strikes power、 surges and microwave ovens. 比特错（bit error）：传送单个的比特也会出现差错；突发性差错（burst error）：几个连续的比特丢失。原因：闪电、电源波动或微波

16、干扰,B. Error occurrs at packet level: a complete packet is lost by the network one reason is that the packet contains an uncorrectable bit error and therefore has to be discarded. Another reason is that one of the nodes that has to handle the packet is so overloaded that it has no to store the packet

17、. 发生在分组级：网络丢失了整个分组。原因：分组含有不可纠正的比特错；必须处理分组的一个结点，由于过载而没有空间存放该分组。,C. Error occurrs at the node and the link: physical link is cut or the computer it is connected to crashes. 发生在结点和链路级：物理链路被切断或连接的计算机崩溃了。,1.1.4 Performance性能“First get it right and then make it fast”“先使它对，再使它快”,1. Bandwidth and Latency(带宽

18、和时延),Bandwidth and Throughput带宽和吞吐量,Bandwidth is literally a measure of the width of a frequency band. For example a voice-grade telephone line supports a frequency band ranging form 300HZ to 3300HZ,it is said to have a bandwidth of (3300Hz300Hz=)3000Hz.It refers to the range of signals that can be

19、accommodated. 带宽：频带宽度的度量。如音频级电话线路，支持300Hz到3300Hz范围内的频带，那么它的带宽为3300Hz300Hz=3000Hz。带宽是指能容纳信号的范围。,Bandwidth of a communication link refer to the number of bits per second that can be transmitted on the link. We may say that the bandwidth of an Ethernet is 10Mbps （Mega bits per second） 通信线路的带宽指链路上每秒钟所能传

20、送的比特数。例如：以太网的带宽是10Mbps（单位：兆 比特/秒）,Throughput refer to the measured performance of a system. 吞吐量：一个系统的测量性能。 Effective end to end throughput: 有效的端到端吞吐量： Throughput=TransferSize/TransferTime A pair of nodes connected by a link with a bandwidth of 10Mbps might achieve a throughput of only 2 Mbps. This w

21、ould mean that an application on one host could send data to another host at 2Mbps. 由一段带宽为10Mbps的链路连接的一对结点可能只会达到2 Mbps的吞吐量，即一个主机上的应用进程能够以2Mbps的速度向另一个主机的对应的应用进程发送数据。,Round-Trip Time 网络的往返时延（RTT） 总时延： Latency=Propagation+Transmit+Queue 传播时延:Propagation=Distance/Speed of Light 发送时延：Transmit=Size/Bandwi

22、dth 等待时延： Queue,3.Application performance needs 应用的性能需求 Requirement is the number of the bits per second that is needs to transmit over the network to perform acceptably. 带宽需求指应用正常执行时在网络上每秒所需传送的比特数。 using the right M and K 正确使用M（兆）和K（千）： Network bandwidth, which is often specified in terms of Mbps t

23、he mega in MHz and Mbps means (106)6 powers of 10 Hz 网络带宽，通常以Mbps来定义它的大小 ， Mbps和 MHz中的M等于106Hz Memory is typically measured in powers of 2.The K( in KB) is usually taken to mean 210 .( similarly, MB usually means 220 ) 内存通常以2的幂次方来度量， KB中的K通常表示210。（同样， MB通常为220）,1.1.5 computer network classification计

24、算机网络的分类,1、From switching function 从网络的交换功能分： Circuit switching net 、 message switching net 、 grouping switching net 、 mixed switching net 电路交换网、报文交换网、分组交换网、混合交换网 2、from covered scope 从网络的作用范围分： WAN（Wide Area Network）、LAN（Local Area Network） 、MAN（Metropolitan Area Network） 广域网、局域网、城域网 3、from the user

25、 of network 从网络的使用者分： Private-Network、 Public-Network 专用网、公用网,LAN classification: client-server net, peer net, mixed net局域网的分类：基于服务器的网络和对等网络，混合型网 络三大类,Server: computer or other facility that provides net user with shared resources, such as file server and print server. 服务器:可为网络中的用户提供共享资源的计算机或设备，分为文件

26、服务器，打印服务器 Client: computer that receives service or visits the shared resource on the server. 客户机:接受服务或需要访问服务器上的共享资源的计算机,1.2 Network System Architecture 网络体系结构,1.2.1 Layering and Protocol(分层和协议) protocol：the abstract objects that make up the layers of a network system(构成网络系统各层的抽象对象) （1） Protocol def

27、inition: some rules for data exchanging on the network. 协议定义：为进行网络中的数据交换而建立的规则（标准或约定） （2） Protocol Composing: 组成：,ASyntax: prescribethe formatof data in correspondence and information control 语法：规定要通信的数据和控制信息的格式 BSemanteme: how to write specific control information 语义：具体的控制信息应该如何写 C. Synchronization

28、: prescribe the sequence for sending message and the sequence for receiving message to make them synchronal. 同步：规定发送数据的计算机按照什么顺序发送，接收数据的计算机按照什么顺序接收使它们保持同步.(He didnt pass the exam),Network Architecture 网络体系结构 （1）Definition: exact definition of the function of computer network and its composing (inclu

29、de hardware and soft ware) 定义：是计算机网络及其组成部分（硬件和软件）的功能的精确的定义 （2） It should be constituted by three parts.应由三部分组成： A Physical part: computer system, communication system 物理结构：网络中所有的硬件设备：计算机系统，通信系统，、 B Logical part ：software for communication: operating system, communicating module, describe the basic c

30、ommunicating operation: data inputting, storage, sending 逻辑结构：进行网络通信的基本软件：操作系统，通信模块，、，描述网络通信的基本操作：数据的输入，存储，发送，,C. Software part：software designed to improve the quality of data transmitting based on logical structure: failure diagnosis , channel control, 软件结构:在逻辑结构的基础上为了改善传输数据的质量而设计的软件：故障诊断（硬件和软件故障）

31、，信道控制，、 （3）well- known network architecture 著名的网络体系结构： SNA（IBM公司），DNA（DEC公司）,1.2.2 OSI Architecture(体系结构) host 终端主机 终端主机 host,One or more nodes within the network 网络中有一个或多个结点,Application 应用层,Presentation 表示层,Session 会话层,Transport 传输层,Network 网络层,Data link 数据链路层,Physical 物理层,Application 应用层,Presentat

32、ion 表示层,Session 会话层,Transport 传输层,Network 网络层,Data link 数据链路层,Physical 物理层,Network 网络层,Data link 数据链路层,Physical 物理层,Network 网络层,Data link 数据链路层,Physical 物理层,Flow of information信息的流动过程 其中： is protocol of application 为应用层的协议 is protocol of presentation为表示层的协议,Application应用层,Presentation表示层,Session会话层,

33、Transport传输层,Network网络层,Data link链路层,Physical物理层,system系统A,Application应用层,Presentation表示层,Session会话层,Transport传输层,Network网络层,Data link链路层,Physical物理层,system系统B,Transport medium传输介质,Original data,Original data,Original data,Original,Original,Original,Original,Original,concept 基本概念 1.Entity: any hardw

34、are or soft-procedure that can receive or send message. 实体：任何可以发送或接收信息的硬件或软件进程 2.Service: At the communication between two entities, make the (N) layer to provide service to its up-layer (N+1) . 服务：两个（N）实体间的通信，使（N）层能够向上一层（N+1）层提供服务,3.Difference between protocol and service: 协议和服务的区别： (1) protocol is

35、 horizontal, service is vertical 协议是水平的，服务是垂直的 (2) service user of （N） can see service of （N） but not see protocol of （N） （N）服务用户可以看见（N）服务可是看不见（N）协议 4. Protocol Data Unit: The current-layer user data (next layer protocol data unit)+ current-layer protocol control information. 协议数据单元（PDU）：本层的用户数据（下一层的协议数据单元）+本层的协议控制信息,Connec