计算机专业英语的课文与翻译

精品文档 1欢迎下载 Unit 8 Computer Networking Text 1 Data Communications The end equipment can be computers printers keyboards CRTs and so on They are either generates the digital information for transmission or uses the received digital data This equipment generally operates digital information internally in word units DTE is data terminal equipment A station controller STACO is the corresponding unit at the secondaries At one time the DTE was the last piece of equipment that belonged to the subscriber in a data link system Between the DTEs first is the modem and then is the communications equipment The communication equipment is owned and maintained by Telco Data communications equipment DCE accepts the serial data stream from the DTE And DCE converts it to some form of analog signal suitable for transmission on voice grade lines At the receive end the DCE performs the reverse function It converts the received analog signal to a serial digital data stream The simplest form of DCE is a modem modulator demodulator or data set At the transmit end the modem can be considered a form of digital to analog converter While at the receive end it can be considered a form of analog to digital converter 参考译文 数据通信 终端设备可以是计算机 打印机 键盘 CRT 等 它们可以生成要发送的数字信息 也可以使用所接收的数字数据 这种设备通常在内部以字为单位处理数字信息 DTE 一般称为数据终端设备 辅助设备一方的相应设备是工作站控制器 STACO 同时 DTE 也是数据链路系统中属于用户端的最后一个设备 在两个 DTE 之间 先是调制解调器 接 着是属于Telco 电话公司维护的通信设备 数据通信设备 DCE 从DTE 接收串行数据流 并 将其转换成适合于在语音线路上发送的某种模拟信号形式 在接收端 DCE 完成相反的功能 把接收到的模拟信号转换成串行数字数据流 最简单的 DCE 是调制解调器或数据传送机 在 发送端 调制解调器可以视为一种数 模转换器 而在接收端则可视为一种模 数转换器 Text 2 Architecture of Computer Networks Computer network is a complex unit it consists of two or more connected computing units It is used for the purpose of data communication and resource sharing Design of a network and its logical structure should comply with a set of design principles They include the organization of functions the description of data formats and procedure In the following two sections we will discuss two important network architectures the OSI reference model and the TCP IP reference model 1 the OSI reference model 精品文档 2欢迎下载 The OSI open systems interconnection model was created by the ISO This model is a foundation for comparing protocols However more protocols deviate from the rules set up by the OSI model The OSI model has seven layers Note that the OSI model itself is not a network architecture It just tells what each layer should do However ISO has also produced standards for all the layers Each one has been published as a separate international standard 2 the TCP IP reference model TCP IP is a communication protocol it provides many different networking services The TCP IP Internet protocol suite is formed from two standards the TCP Transmission Control Protocol and the IP Internet Protocol TCP means it is on the transport layer IP means it is on the network layer On top of the transport layer is the application layer It contains all the higher level protocols The early ones included virtual terminal TELNET file transfer FTP electronic mail SMTP and domain name service DNS As we know TCP IP is the foundation of the Internet These protocols are continually changing and evolving to support the needs of the user community 参考译文 计算机网络结构 计算机网络是由两个或多个计算机设备互连而成的一种复合系统 它用于数据通信和 资源共享 网络设计及其逻辑结构应该遵循一套设计原则 其中包括 功能的组织以及数 据格式和过程的说明 在下面的两小节里 我们将讨论两个重要的网络体系结构 即 OSI 参考模型和 TCP IP 参考模型 1 OSI 参考模型 OSI 模型 开放系统互联参考模型 是由国际标准化组织 ISO 开发的一个建议 相 对于其他协议来说 此种模式为基础模式 然而 更多的协议是背离 OSI 模型的 OSI 模型有 7 层 应该注意的是 OSI 模型本身并不是一种网络体系结构 它只是说明 每一层应该做什么 然而 ISO 还是对各层制定了标准 每一层都是作为一个单独的国际 标准来颁布的 2 TCP IP 参考模型 TCP IP 参考模型是一种传输协议 提供了许多不同的网络服务 TCP IP 协议组由 TCP 传输控制协议 和 IP 网际协议 两部分组成 TCP 表明是处 于传输层 IP 意为是在网络层 在传输层上面是应用层 应用层包括所有高层协议 早期 的协议包括虚拟终端 TELNET 文件传送协议 FTP 电子邮件 SMTP 和域名服务 DNS 现在我们知道 TCP IP 协议是因特网的基础 这些协议在用户们的支持下不断地改变 和进化着 Text 3 Local Area Network A LAN Local area data network is a group of computers The work devices connected together usually within the same building By definition the 精品文档 3欢迎下载 connections must be high speed and relatively inexpensive e g token ring or Ethernet For example a LAN may be used to interconnect workstations distributed around offices within a single building or a group of buildings such as a university campus LANs consist of carefully selected groups of components hardware and software They are configured for the specific requirements of the organization A LAN is generally limited to the size of a department or an organization And a LAN often consists of 2 to 100 devices LANs usually contain resources such as servers printers and connections to other networks through internetworking devices The internetworking devices include switches and routers In the next section we will discuss the structure of the different types of LAN 1 Topology Most wide area networks such as the PSTN use a mesh sometimes referred to as a network topology With LANs however the limited physical separation of the subscriber DTEs allows simpler topologies to be used The four topologies in common use are star bus ring and hub The most widespread topology for LANs designed to function as data communication subnetworks for the interconnection of local computer based equipment is the hub topology It is a variation of the bus and ring 2 Transmission media Twisted pair coaxial cable and optical fibre are the three main types of transmission medium used for LANs 3 Medium access control methods Two techniques have been adopted for use of the medium access control in the LANs One is carrier sense multiple access with collision detection and the other is control token 参考译文 局域网 局域数据网 局域网 由若干计算机组成 通常是一幢楼内的工作设备被连接在一起 通过定义可知 这种连接一定是高速并且相对廉价的 如 令牌网和以太网 例如 一个 局域网可以把一幢楼里或像大学校园内楼群里的各个办公室的工作站连在一起 局域网是由精心挑选的各组设备 硬件和软件 构成的 它们根据组织的各种特殊需 要来配置 局域网的大小一般限制在一个部门或者一个组织 由 2 100 台电脑组成 局域 网经常包含一些资源 如一些服务器和打印机 而且可以通过网络设备与其他的网络连接 这些网络设备包括交换机和路由器等 接下来 我们将讨论不同类型局域网的结构 1 拓扑结构 大多数广域网 如公共电话交换网 PSTN 使用网状 有时称为网络 拓扑结构 而 局域网由于用户数据终端设备相距很近 可采用简单的拓扑结构 常用的有星形 总线 环形和集线器等 4 种拓扑结构 精品文档 4欢迎下载 应用最广的 用于互连本部门计算机设备以进行数据通信的局域网拓扑结构是集线器 拓扑结构 这种拓扑结构是总线和环形拓扑结构的变种 2 传输媒体 双绞线 同轴电缆和光纤是局域网采用的 3 种主要传输媒体 3 媒体访问控制方法 局域网中采用了两种媒体访问控制技术 一种是载波侦听多路访问 冲突检测技术 CSMA CD 另一种是令牌控制技术 Text 4 Internet The Internet is used by millions of people across the world to communicate business and personal information The Internet is huge Then we will talk about the difference of an internet and the Internet An internetinternet note the lower case i is a computer network It allows computers with distinctive software and hardware to communicate Many kinds of computers can be connected to an internet Each computer can serve a specialized role It offers a wide variety of services to its users The InternetInternet is specific kind of internet In The Internet Passport the Internet will be defined as the network of networks It follows a set of rules known as the Internet Protocol IP suite But what does this mean to you It means that any computer that is connected to the Internet can communicate with any other Internet computer From the user s perspective this works much like the telephone system works You can dial from your phone to any other phone on the system no matter what kind of telephone you have you only need to know the phone number of the person you want to reach With an Internet connection you can get some of the basic services available are E mail It s a fast easy and inexpensive way to communicate with other Internet users around the world Telnet It allows a user to log into a remote computer as though it were a local system FTP It allows a user to transfer virtually every kind of file that can be stored on a computer from one Internet connected computer to another Usenet news It s a distributed bulletin board which offers a combination news and discussion service on thousands of topics World Wide Web WWW It s a hypertext interface to Internet information resources Also through an Internet connection you can access online library catalogs copy computer files or software from archives access databases for teaching or research obtain free electronic books use educational and information services 精品文档 5欢迎下载 use directory services to find Internet users access supercomputer sites It was estimated that at this rapid growth everyone in the world would have an e mail address in the near future 参考译文 互联网 因特网是世界上很多人用来进行商业贸易和个人信息交流的网络 它非常巨大 接下 来 我们将讨论互联网及因特网 互联网互联网 internet 注意小写字母 i 是一种计算机网络 该网络上的计算机在通信 时可以使用不同的软件和硬件 多种计算机都可以连入互联网 每台计算机都可以有一独 特作用 一个互联网可以向它的用户提供各式各样的业务 因特网因特网 Internet 是一种专用互联网 因特网在它的证书中定义为网络的网络 该网 络使用了一组叫做互联网协议 IP 组的规则 但对你来说 这意味着什么呢 这表明连接到因特网上的计算机可以与因特网上任何 其他计算机通信 从用户的角度来看 其工作方式很像电话系统的工作方式 在电话系统 内 可以从你的电话机拨打任何其他电话 而不管你使用什么样的电话机 你只需知道对 方的电话号码即可 你可以通过因特网得到的基本服务如下 电子邮件 它是与世界范围内的因特网用户进行联系的一种快速 方便 廉 价的交流方式 远程登录 允许用户连接到远程计算机上 就像这台远程计算机是本地机一 样 文件传输协议 该协议可以将存储在计算机上的各种文件 从因特网上的一 台计算机传送给另一台计算机 新闻组网络系统 一种分布式的电子公告牌 它能提供有关上千种话题的新 闻和讨论服务 万维网 一种因特网信息资源的超文本界面 访问在线图书馆目录 从计算机档案库存储器中拷贝文件或软件 访问教学或科研数据库 获取免费电子图书 使用教育和信息服务 使用目录服务以查找因特网用户 访问超级计算机站点 估计以这样的高速发展 在不久的将来世界上每个人都将拥有至少一个电子邮件地址 Text 5 The World Wide Web The World Wide Web also known as WWW or Web is one of the fastest growing Internet software applications It is an architectural framework It linked documents spread out over thousands of machines for accessing all over the Internet 精品文档 6欢迎下载 The World Wide Web ties the computers together into a vast collection of interactive multimedia resources The WWW is a way of exchange information between computers on the Internet The Web is built around hypertext and hypermedia A hypertext document has certain keywords or phrases linked to other online documents A person reading a hypertext document about mobile phone for example might be able to select the highlighted word Nokia 3310 and he call up another document giving more information about that particular type With documents intertwined by links into a web of information you can select paths to browse online resources a process often referred to as surfing Hypermedia extends the concept of hypertext to other forms of information They include images sounds and even video clips If a person read a hypermedia document about mobile phones then he might select a video show of a phone and hear the ring of it The World Wide Web also subsumes previous Internet information systems such as Gopher and FTP These resources can still be accessed through the Web But the Web offered by these more restricted connection methods Now the Web provides a wealth of additional capabilities Thousands of computers around the world are now connected to the Web They offer a huge variety of information and services to visitors These online documents are generally referred to as pages They are composed and supported by various pe