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1、Computer Science Chapter 4 第 1 页 共 21 页Computer Science an Overview（10 th edition）Chapter 4 Networking and the Internet (组网及因特网)In this chapter we discuss the area of computer science known as networking, which encompasses (vt.包括,包含) the study of how computers can be linked together to share informa
2、tion and resources. Our study will include the construction and operation of networks, applications of networks, and security issues. A prominent (重要的,突出的) topic will be a particular worldwide (遍及世界的 ,全世界的) network of networks known as the Internet.prominent adj.突起的（突出的） ，杰出的（重要的，著名的）-a prominent no
3、se 大鼻子-a prominent doctor 著明的医生本章讨论计算机科学中称为网络的领域，包括学习如何将计算机连接起来共享信息资源。研究的内容包括网络的结构与操作、网络的应用以及网络安全问题，学习一个重点主题是遍布世界范围的特殊网络因特网。The need to share information and resources among different computers has led to (导致) linked computer systems, called networks, in which computers are connected so that data ca
4、n be transferred from machine to machine. In these networks, computer users can exchange messages and share resourcessuch as printing capabilities,(功能,能力,容量) software packages, and data storage facilities(设备 ,容易)that are scattered (v.分散,撒布) throughout the system. The underlying software required to
5、support such applications has grown from simple utility packages into an expanding system of network software that provides a sophisticated (vt.使复杂,使精巧,使世故) network wide infrastructure. In a sense, network software is evolving into a network wide operating system. In this chapter we will explore thi
6、s expanding field of computer science.scatter v.分散 （散开）, 散播 （撒布）To cause to separate and go in different directions.散开：使朝不同的方向分离和走开-Do not scatter your strength .不要分散精力。To distribute loosely by or as if by sprinkling; strew:散落：洒或如同洒开一般分散；散播：-The farmer scattered the corn in the yard for the hens.(母鸡
7、)农民把谷子撒在院子里喂鸡。人们对不同计算机之间共享信息和资源的需求产生了相互连接的计算机系统，它被称为网络（network） 。计算机通过网络连接在一起，数据可以从一台计算机传输到另一台计算机。在网络中，计算机用户可以相互交换信息，并且可以共享分布在整个网络系统中的资源，如打印功能、软件包以及数据存储设备。用于支持这类应用的基础软件也已经从单一的实用软件包升级为扩展网络软件系统，从而可以提供一个复杂、先进的网络范围的基础架构。从某种意义说，网络软件正发展成为网络范围的操作系统。本章将探讨计算机科学中这个不断发展的领域。4. 1 Network Fundamentals （网络基础）We be
8、gin our study of networks by introducing a variety of basic networking concepts.我们通过介绍多种基本的网络概念开始学习网络。Network Classifications （网络的分类）A computer network is often classified as being either a local area network (LAN), a metropolitan (大城市的,大都会的) area network (MAN), or a wide area network (WAN). A LAN n
9、ormally consists of a collection of computers in a single building or building complex. (综合建筑 ) For example, the computers on a university campus or those in a manufacturing Computer Science Chapter 4 第 2 页 共 21 页plant might be connected by a LAN. A MAN is a network of intermediate (a.中间的 n.媒介) size
10、, such as one spanning (v.覆盖,跨越 n.跨度) a local community. A WAN links machines over a greater distanceperhaps in neighboring cities or on opposite sides of the world.计算机网络通常分为局域网（local area network，LAN ） 、城域网（metropolitan area network，MAN ）和广域网（wide area network，WAN） 。局域网通常由一幢建筑物或者综合楼群中的若干计算机组成。例如，大学
11、校园的计算机或者工厂中的计算机都可以用局城网连接。城域网属于中型网络，例如可以覆盖某一社区。广域网连接的计算机覆盖范围更广可以是相邻城市，也可以是在世界的另一端。Another means (n.用作 sing方法,手段) of classifying networks is based on whether the networks internal operation is based on designs that are in the public domain (领域,领土) or on innovations (新方法,新技术) owned and controlled by a
12、particular entity such as an individual or a corporation. A network of the former type is called an open network; a network of the latter type is called a closed, or sometimes a proprietary,(专用的,私有的,业主的) network. Open network designs are freely circulated (vt.(使) 运行, (使) 循环) and often grow in popula
13、rity (普及,流行) to the point that they ultimately (最后,最终) prevail over (胜过) proprietary approaches whose applications are restricted by license fees and contract conditions.prevail vi.(常与 against, over 连用)战胜(胜过), 普遍(盛行,流行)-Truth is great and will prevail.真理是至高无上的，且必将获胜。-This old custom does not prevail
14、 now.这种旧风俗现在已经不流行了。网络分类的另一种方式是根据网络的内部运行是否基于这样的事实：是按公共领域的方法设计的，还是基于特定实体（如个人或公司）所拥有并掌握的创新方法。前一种类型的网络称为开放式（open）网络，后者称为封闭式（closed ）网络，有时也称为专用（proprietary）网络。自由运行的开放网络在普及方面的发展最终会胜过专用网，许可费和合同限制了专用网的应用。The Internet (a popular worldwide network of networks that we will study shortly) is an open system. In
15、particular, communication throughout the Internet is governed (统治,支配, 管理) by an open collection of standards known as the TCP/IP protocol (协议) suite,(组,套) which is the subject of Section 4.4. Anyone is free to use these standards without paying fees or signing license agreements. In contrast,(相反,大不相
16、同 ) a company such as Novell Inc. might develop proprietary systems for which it chooses to maintain ownership (所有权,主权) rights, allowing the company to draw (提领,拉) income from selling or leasing (租) these products. draw v.拉( 拖), 取(拿), 划(画)-drawn by a horse 马拉车-draw ones salary 领薪-I like drawing cats.我喜欢画猫。因特网（下面会学到一种很流行的世界范围的网络中的网络）属于开放式系统。尤其是，贯穿因特网的通信是由一组称为 TCP/IP 协议簇的开放标准来控制的（见 4.4 节） 。任何人都可以自由地使用这些标准，而不需要付费或签署许可协定。相反，像 Novell 这样的公司可能开发一些存
