计算机专业英语的课文与翻译

Unit 8 Computer NetworkingText 1 Data CommunicationsThe 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 NetworksComputer 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 modelThe 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 modelTCP/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 NetworkA LAN (Local area data network) is a group of computers. The work devices connected together usually within the same building. By definition, the 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 throughinternetworking devices. The internetworking devices include switches and routers.In the next section we will discuss the structure of the different types of LAN.(1)TopologyMost 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 mediaTwisted pair, coaxial cable and optical fibre are the three main types of transmission medium used for LANs.(3)Medium access control methodsTwo 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。