Section A Network Fundamentals 课文A 网络基本原理,Unit 7 Computer Network 第7单元 计算机网络,刘晓璐 讲师,The need to share information and resources among different computers has led to linked computer systems, called networks, in which computers are connected so that data can be transferred from machine to machine. 在不同计算机之间共享信息和资源的需要，导致了相互连接的计算机系统的产生。这种相互连接的计算机系统被称为网络。在网络中，计算机连接在一起，从而数据可以从一台计算机传输到另一台计算机。,In these networks, computer users can exchange messages and share resourcessuch as printing capabilities, software packages, and data storage facilitiesthat are scattered throughout the system. 在网络中，计算机用户可以交换信息，并共享分散在整个网络系统的资源，如打印能力、软件包以及数据存储设备。,插入语,定语从句，修饰resources,The underlying software required to support such applications has grown from simple utility packages into an expanding system of network software that provides a sophisticated network wide infrastructure. underlying,ndlaadj.潜在的;基础的;表面下的 sophisticatedsfstketdadj.(机器、装置等)高级的,精密的;(方法)复杂的 infrastructurenfrstrkt(r)n.基础设施；基础建设 支持这类应用所需的基本软件，已经从简单的实用软件包发展成一个不断扩展的网络软件系统，该系统提供了一个复杂的网络范围的基础结构。,In a sense, network software is evolving into a network wide operating system. evolve into逐渐发展(进化、演变)成 从某种意义上说，网络软件正在演变成一个网络范围的操作系统。,I. Network Classifications,A computer network is often classified as being either a local area network (LAN), a metropolitan area network (MAN), or a wide area network (WAN). metropolitan,metrpltnadj.大都会的；大城市的；宗主国的；大主教教区的 一、网络分类 计算机网络常常划分为局域网、城域网和广域网。,A LAN normally consists of a collection of computers in a single building or building complex. For example, the computers on a university campus or those in a manufacturing plant might be connected by a LAN. complex综合建筑群;综合大楼 plant工厂;成套设备 局域网通常由一幢建筑物或一个建筑群中的若干计算机组成。例如，大学校园里的计算机或制造工厂中的计算机可以用局域网连接。,A MAN is a network of intermediate size, such as one spanning a local community. A WAN links machines over a greater distanceperhaps in neighboring cities or on opposite sides of the world. spanspnvt.跨越;遍及 communitykmju:ntn.社区;社会团体;群落 城域网属于中型网络，如一个覆盖某一社区的网络。广域网连接地理范围更广的计算机，这些计算机或许在相邻的城市，或许在地球相反的两面。,Another means of classifying networks is based on whether the networks internal operation is based on designs that are in the public domain or on innovations owned and controlled by a particular entity such as an individual or a corporation. domaindmenn.范围，领域； innovationnvenn. 革新，创新 网络分类的另一种方式是根据网络的内部运行是基于无专利权保护的设计还是基于特定实体（如个人或公司）所拥有和控制的革新。,宾语从句,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 network. proprietaryprpratradj.专有的，专利的 前一种类型的网络称为开放式网络，后一种类型的网络称为封闭式网络，有时也称为专有网络。,The Internet is an open system. In particular, communication throughout the Internet is governed by an open collection of standards known as the TCP/IP protocol suite. Anyone is free to use these standards without paying fees or signing license agreements. suiteswi:tn.计（软件的）套件 因特网 属于开放式系统。尤其是，整个因特网的通信是由一组称为TCP/IP协议组的开放标准来控制的。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议。,In contrast, a company such as Novell Inc. might develop systems for which it chooses to maintain ownership rights, allowing the company to draw income from selling or leasing these products. Inc. (缩写)incorporated (责任有限)公司 leaseli:svt.出租; 租借 incomenkm n.收入，进款； 相反，像Novell股份有限公司这样的公司可能选择为其开发的系统保留所有权，通过出售或出租这些产品获得收入。,Networks based on such systems are examples of closed networks. 基于这类系统的网络属于封闭式网络的例子。,Still another way of classifying networks is based on the topology of the network, which refers to the pattern in which the machines are connected. The bus topology, ring topology, and star topology are three popular topologies. topologytpldn.地质学; 拓扑结构 还有一种网络分类方法，它基于网络的拓扑结构，即计算机相互连接的模式。总线拓扑结构、环形拓扑结构和星形拓扑结构是3种流行的拓扑结构。,Of these, the star network is perhaps the oldest, having evolved from the paradigm of a large central computer serving many users. paradigmprdam n.范例，样式，模范； 其中，星形网络或许是最古老的，这种网络由一台大型中央计算机服务许多用户的范式演变而来。,As the simple terminals employed by these users grew into small computers themselves, a star network emerged. 随着这些用户所使用的简单终端本身发展成小型计算机，星形网络也就出现了。,A point to emphasize is that the connections between machines in a network do not need to be physical. Wireless networks, using radio broadcast technology, are becoming quite common. emphasizeemfsazvt.强调，着重 需要强调的一点是，在一个网络中，计算机之间的连接并不一定是物理连接。使用无线广播技术的无线网络正在变得相当常见。,Protocols协议,For a network to function reliably, it is important to establish rules by which network activities are conducted. Such rules are called protocols. functionfknvi.工作;运转;运行;发挥功能; reliablyrlabladv.可靠地，确实地 conductkndktvt. 控制 为了网络可靠运行，确立进行网络活动所遵循的规则很重要。这类规则称为协议。,By developing and adopting protocol standards, venders are able to build products for network applications that are compatible with products from other venders. vendervendn.卖主, 售卖者, 供应商 compatiblekmptbladj.兼容的，相容的 通过开发和采用协议标准，不同厂商制造的网络应用产品能够相互兼容。,Thus, the development of protocol standards is an indispensable process in the deve