英语翻译.COMPUTER NETWORKS Communication between distributed communities of computers is required for many reasons.At a national level,for example,computers located in different parts of the country use public communication services to exchange e

英语翻译.COMPUTER NETWORKS Communication between distributed communities of computers is required for many reasons.At a national level,for example,computers located in different parts of the country use public communication services to exchange e
英语翻译
.COMPUTER NETWORKS
Communication between distributed communities of computers is required for many reasons.At a national level,for example,computers located in different parts of the country use public communication services to exchange electronic messages (mail ) and to transfer files of information from one computer to another.Similarly,at a local level within,say,a single building or establishment,distributed communities of computer-based workstations use local communication networks to access expensive shared resources for example,printers,copiers,disks and tapes,etc.that are also managed by computers.Clearly,as the range of computer-based products and associated pubic and local communication networks proliferate,computer-to-computer communication will expand rapidly and ultimately dominate the field of distributed systems.
Although the physical separation of the communicating computers may vary considerably from one type of application to another,in general a computer communication network can be represented diagrammatically as shown in Fig.11-2.At the heart of any computer communication network is the data communication facility which,as has been outlined,may be a PSDN,a private LAN or perhaps a number of such networks interconnected together.However,irrespective of the type of data communication facility,an amount of hardware and software is required within each attached computer to with the establishment of a communication channel across the network and with the control of the flow of messages across this channel.The provision of such facilities is only part of the network requirements,however,since in many applications the communicating computers may be of different types.This means that may use different programming languages and,more importantly,different forms of data representation interface between user (application ) programs,programs,normally referred to as application processes or APS,and the underlying communication services may be different.For example,one computer may be a small single-user computer,while another may be a large multi-user system.
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英语翻译.COMPUTER NETWORKS Communication between distributed communities of computers is required for many reasons.At a national level,for example,computers located in different parts of the country use public communication services to exchange e
计算机网络
沟通分布式社区的电脑是需要有很多原因.在国家一级,举例来说,电脑设在该国不同地区使用公共通信服务,以交换的电子讯息（电子邮件） ,并进行文件传输,信息从一台计算机到另一个地方.同样,在地方一级,也就是说,一个单一的建筑物或场所,分发给社区的以计算机为基础的工作站,利用当地的通讯网络,以获取昂贵的共享资源,例如,打印机,复印机,光盘和录音带等,也有管理电脑.显然,随着一系列以计算机为基础的产品及相关耻毛和当地通信网络扩散,计算机与计算机之间的通信将迅速扩大,并最终称霸领域的分布式系统.
虽然物理隔离的计算机进行沟通,可能有很大的差别,从一类应用到另一个,在总体上是一个计算机通信网络,可为代表的图,显示图.11-2 .处于核心地位的任何一台计算机通信网是数据通信设施,如已经概述,可能是一个PSDN ,一个私人局域网或者多个这样的网络互联在一起.不过,无论其类型的数据通信设施,又划拨了硬件和软件,是需要在每一个附加电脑与建立一个沟通渠道,在整个网络,并与控制流量的讯息跨越这个频道.提供这些设施只是其中一部分的网络需求,但是,由于在许多应用中通信计算机可能是不同类型的.这意味着,可能使用不同的编程语言,而且更重要的是,不同形式的数据表示接口之间的用户（应用）程式,程式,通常被称为应用程序或接入点,以及底层通信服务可能有所不同.举例来说,一台电脑可能是一个小型的单用户计算机,而另一个可能是一个大型的多用户体系.