电气专业英语课文翻译(5)

There are three major categories of networks distinguished primarily by geography: wide-area networks , metropolitan-area networks , and local-area networks.

现在有三种通过地域分类成的网络，广域网 城域网 局域网。

the Internet—a world wide network of computer networks—makes it possible for you to connect your computer (equipped with the appropriate hardware and software)to a wide variety of remote computer. The remote computers may be thousands of miles away, yet you can search libraries of software, access news and other information, conduct business, and meet people with interests or hobbies similar to your own around the globe.

广域网提供了贯穿一个国家或者整个世界的通信，电话网络是一个最普通的例子，他经常被视为一个独立的实体，尽管他是由一类单独的公司建立的。

尽管手机系统创造了一个声音连接在你的电话和世界上任意一部电话之间。网络，一个世界的计算机网络，（配备适当的硬件和软件）使你的计算机连接到一个任意远的计算机成为了可能。远程计算机可能有数千英里之外，你还可以搜索库的软件，获取新闻和其他信息，进行业务，并满足人民的兴趣、联系世界各地有相同爱好的人。

The Internet isn‘t the only worldwide computer network. International companies have private networks to link offices in different countries together electronically to form 24-hour-a-day business operations. Commercial public networks like CompuServe, Prodigy, and America Online are also used by people around the world. As these networks have grown in popularity, they have begun to interconnect, creating a global collection of people and computers that are able to electronically communicate with one another.[3]

互联网并不是唯一的全球计算机网络，国际公司有专用的网络来连接，把不同国家的办公室连接到一起制定一个24小时都在运作的商业。公共商业网络，如 也同样被全世界的人使用，伴随着这些网络渐渐普及，他们开始互联，创造一个能让全球的人和计算机能以电子方式互相沟通。

Metropolitan-area Networks

Metropolitan-area networks (MANs) provide communications across and among major metropolitan areas such as New York, Chicago, or Los Angeles. Public-safety agencies such as police and fire departments, and dispatch-oriented companies, like Federal Express, operate and maintain their own private networks. They use MANs to allow their mobile ―out-of-office‖ workers to talk to and pass data back and forth to one another.

城域网提供通信在主要都市地区如纽约，芝加哥，或洛杉机。公共安全机构如警察和消防部门，和dispatch-oriented公司，像联邦快递，操作和维护他们自己的私人网络。他们用城域网使他们的移动电话和自由活动的工人交谈，来回传递数据到另一个。

more recent development is the public voice and data networks. An example you may be familiar with is the cellular telephone network, which is made possible by dividing a geographical area into hexagonal-shaped cells, each with a base station.[4] Each cell, which is approximately 10 miles(16 kilometers) across, has its own antenna. Like the public telephone network, public MANs eliminate the need for individuals and organizations to build and operate their own networks.

最近的发展是公共数据和语音网络。一个例子是你很熟悉的蜂窝电话网络，这可能是由一块地理区域划分为六角型细胞，每个基站。每一个细胞，这大约是10英里（16公里），有其自己的天线。像公共电话网，公共人的消除需要个人和组织的建立和经营自己的网络。

Local-area Networks

Local-area networks (LANs) provide communications within specific buildings or facilities. This type of network could be used, for example, in a company where computers are located in the sales, accounting, production, and purchasing departments. Each computer would handle the applications unique to its department. When communication among the computers is required, the computers pass data to one another over the network. For example, purchasing information must be passed to the accounting department for inclusion in the accounts payable system, or production-scheduling information must be passed to the purchasing department for use by the purchasing and inventory systems.

局域网（LAN）提供在特定的建筑物或设备通信。这种类型的网络可以使用，例如，在一个公司的电脑都在销售，财务，生产，采购部门。每台计算机都会处理本部门。当计算机之间需要进行通信，计算机通过数据在网络上彼此。例如，采购信息必须传送到会计部列入应付账款，或生产调度信息必须传送到采购部门采购和存货系统使用。

Local-area networks have many different topologies, or ways in which computer can be connected to the network. Today, the two most common topologies are called ring and bus networks.

局域网有多种不同的拓扑结构，使计算机可以连接到网络。今天，两种最常见的拓扑结构可以是环形网络和总线网络

Ring Networks

Computers on a ring network are hooked together one after the other to form one continuous ring. To access each computer, a piece of software called a token is passed around the ring. A token is the electronic equivalent of an envelope. It contains a destination address and a fixed amount of information. The most popular token method is called token passing, in which one token at a time passes from computer to computer and carries messages around the network.

在环形网络中的电脑，是一个一个连接起来的，来形成一个连续不断的环形。为了访问每台电脑，被称作令牌的一系列软件通过周围的环。令牌是电子设备中的信封，它包括了目的地地址和一些固定量的信息。最常用的令牌方法被称为令牌传递，其中一个令牌可以同时向网络中的其他计算机传递信息。

· Bus Networks

On a bus network computers are simply connected by a cable routed along a path in the vicinity of each device that must be connected to it. The most popular bus network is called Ethernet. Bus networks allow multiple messages to be sent simultaneously. This is often accomplished by ―listening‖ to the network to see if any computer is transmitting. If the network is free, the computer can send its data. If two computers accidentally send data at the same time, a collision occurs, and after detecting the collision, the computers wait a random amount of time to transmit again. T …… 此处隐藏：5308字，全部文档内容请下载后查看。喜欢就下载吧 ……