(精品)ch01_Introduction

,1.,*,NCEPU,Data Communications&Networking,1.,*,NCEPU,Chapter 1,Introduction,第一章 绪论,Department of Electronic and Communication Engineering,NCEPU,1,截至,6,月底，至,6,月底，我国网民数量达到,5.38,亿，是,15,年前的,867,倍。,IPv6,地址数大幅增长，进入全球排名三甲。我国正快速步入网络时代。,我国手机网民数量达到,3.88,亿，手机首次超越台式电脑成为第一大上网终端。,2,3,4,5,Chapter 1,Introduction,绪论,6,1-1 DATA COMMUNICATIONS,数据通信,The term,telecommunication,means communication at a distance.The word,data,refers to information presented in whatever form is agreed upon by the parties creating and using the data.,Data communications,are the exchange of data between two devices via some form of transmission medium such as a wire cable.,Components,组成,Data,Representation,数据表示,Data Flow,数据流,Topics discussed in this section:,7,Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.The,effectiveness,of a data communications system depends on four fundamental characteristics:,Delivery.,传递性,The system must deliver data to the correct destination,Accuracy.,准确性,Timeliness.,及时性,Jitter.,抖动性,Jitter refers to the variation in the packet arrival time.(audio or video),8,Figure 1.1,Five components of data communication,1.Message,报文,2.Sender,发送方,3.Receiver,接受方,4.Medium,介质,5.Protocol,协议,9,Data Representation,数据表示,Text,文本,Numbers,数字,Images,图像,Audio,音频,Video,视频,10,Figure 1.2,Data flow(simplex,half-duplex,and full-duplex),p6,数据流分为单工、半双工和双工,11,1-2 NETWORKS,网络,A,network,is a set of devices(often referred to as,nodes,)connected by communication,links,.A node can be a computer,printer,or any other device capable of sending and/or receiving data generated by other nodes on the network.,网络是指由介质链路连接在一起的一系列设备（常常被称为网络节点）,Distributed,Processing,分布式处理,Network,Criteria,网络准则,Physical Structures,物理结构,Network Models,网络模型,Categories of Networks,网络分类,Interconnection of Networks:Internetwork,网络互联：因特网,Topics discussed in this section:,12,1.2.1,Distributed processing,分布式处理,Advantages:,Security/encapsulation,安全性,/,封装性,Distributed databases,分布式数据库,Faster problem solving,更快的解决问题方式,Security through redundancy,通过冗余达到安全性,Collaborative processing,协作处理,13,安全性,网络准则,可靠性,性能,性能：多种形式衡量，包括传输时间和响应时间。性能取决于多种因素用户数量、传输介质类型、所连接的硬件能力以及软件效率,可靠性：出现故障的频率、一条链路从故障恢复所花费的时间,可靠性：保护数据免受未授权的访问,1.2.2,Network Criteria,网络准则,14,Figure 1.3,Types of connections:point-to-point and multipoint,点到点和多点,Reserved capacity VS Shared capacity,连接类型,1.2.3,物理结构,Physical Structures,15,Figure 1.4,Categories of topology,物理拓扑结构,16,Figure 1.5,A fully connected mesh topology(five devices),优点,:,专用线路,dedicated links,健壮性,robust,秘密性、安全性,privacy/security,故障识别、排除,fault identification/isolation,缺点：,安装复杂，费用离谱,17,Example,The Lucky Ducky Corporation has a fully connected mesh network consisting of eight devices.Calculate the total number or cable links needed and the number of ports for each devices.,Solution,Number of links=n(n-1)/2=8(8-1)/2=28,Number of ports per device,=n-1=8-1=7,18,Figure 1.6,A star topology connecting four stations,A dedicated point-to-point link only to a central controller,hub,星型拓扑用于局域网中，高速局域网通常用星型拓扑结构,19,Figure 1.7,A bus topology connecting three stations,Used in early Ethernet LANs but they are less,pupular,now,.,总线拓扑是多点配置的,(multipoint),。,Ease of installation;less cabling;,易安装，使用电缆最少，主缆能支持的抽头数和抽头之间的距离都有限制，在各个抽头处的信号反射会降低传输质量。,健壮性差,(robustness),引出线,分接头,20,Figure 1.8,A ring topology connecting six stations,被,IBM,引入令牌环局域网时曾盛行一时，目前要求高速局域网，这种拓扑结构就不流行了。,Example 1.2,If the devices in Example 1.1 are configured as a ring instead of a mesh,how many cable links are required.,21,Figure 1.9,A hybrid topology,混合,:a star backbone with three bus networks,22,1.2.4,Network Models,网络模型,OSI 7-layer model,Internet 5-layer model,1.2.5,Categories of Networks,网络分类,Local Area Network,局域网,Wide Area Network,广域网,Metropolitan Area Network,城域网,Interconnection of Networks:Internetwork,网络互联：因特网,23,Figure 1.10,An isolated LAN connecting 12 computers to a hub in a closet,房间,Currently,LAN size is limited to a few kilometers.,Common LAN topologies:bus,ring,and star.,Speeds are normally 100 or 1000 Mbps,wireless LANs,24,Figure 1.11,WANs:a switched WAN and a point-to-point WAN,WAN:,X.25;ATM,25,1.12,A heterogeneous network made of four WANs and two LANs,Internetwork,heterogeneous,不同种类的,26,1-3 THE INTERNET,因特网,The,Internet,has revolutionized,彻底改变,many aspects of our daily lives.It has affected the way we do business as well as the way we spend our leisure time.The Internet is a communication system that has brought,a wealth of,information,to our fingertips,and organized it for our use.,A,Brief,History,历史简介,The,Internet,Today,(,ISPs),因特网现状（因特网服务提供商）,Topics discussed in this section:,27,ARPA,：,Advanced Research Projects Agency,(,美国国防部,),高级计划研究署,70,年代初的美国深陷在越南战场的泥潭中，不能自拔，而国内的反战呼声一浪高过一浪。美国到了二战后第一个内外交困的年代。虽然这样，但是国内的各种科学技术还是在飞速地发展。,ARPANET,在不断地壮大。,1970,年的,ARPANET,已初具雏形，并且开始向非军用部门开放，许多大学和商业部门开始接入。但是它只有四台主机联网运行，甚至连局域网（,LAN,）的技术也还没有出现。当时用作接口机的,Honeywell DDP516,型小型机的内存只有,12K,。,ARPANET,在洛杉矶的加利福尼亚大学洛杉矶分校、加州大学圣巴巴拉分校、斯坦福大学、犹他州大学四所大学的,4,台大型计算机采用分组交换技术，通过专门的接口信号处理机（,IMP,：,inte