通信英语 第三单元

1、通信英语 unit 3通信英语 unit 3Key Terms ReviewASCII American Standard Code for Information Interchange Expansion slots 扩展槽Integrated circuits 集成电路 Memory内存storage 存储器Socket 插座Media 媒体 媒介 介质Port 接口 端口Device 设备ROM 只读存储器RAM 随机存储器Multimedia 多媒体IC CardMagnetic strip CardSecondary storage 外存Terminal 终端Host/Termin

2、al 主机/终端Binary/Octet/Decimal/Hex 二进制/八进制/十进制/十六进制 通信英语 unit 3 network v. 联网 n. 网络 networking technology 联网技术 specification n. 规格，规范 technical specifications 技术规格 compatible a. 一致的，兼容的，匹配的 This software is compatible with Window XP. 这套软件和Window XP兼容。 scheme n. 方案，设计，方法 model n. 模型，模范，模特儿 pattern n. 样

3、式，模式 mode n. 模式，方式通信英语 unit 3 vendor n. 卖主，供应商 buyer n. 买主 framework n. 框架 packet n. 包，分组 data packet 数据包 layer n. 层 component n. 部件，组件 synchronize vt. 使同步 browser n. 浏览器 an Internet browser 因特网浏览器 format n. 格式通信英语 unit 3 compression n. 压缩 compress vt. 压缩 to compress a file 压缩一个文件 press a button 按一个

4、按钮 compressed air 压缩空气 an air-compressor 空压机 encryption n. 加密 protocol n. 协议 frame n. 帧，框架 access n. 接入，连通 topology n. 拓扑通信英语 unit 3The early development of LANs, and WANs was chaotic（混乱的） in many ways. the early 1980s saw tremendous （极大的） increases in the numbers and sizes of networks. As companies

5、 realized they could save money and gain productivity by using networking technology, they added networks and expanded existing networks almost as rapidly as new network technologies and products could be introduced.局域网、城域网和广域网的发展在很多方面都是混乱无序的，80年代初，网络的规模和数量发展极快，由于公司意识到，利用联网技术，他们可以省钱和提高生产率，因而只要能引入新的网

6、络技术和产品，他们就要扩充现有的网络和添加新的网络。 Paragraph 1 通信英语 unit 3By the mid-1980s, theses companies began to experience growing pains from all the expansions they made. It became harder for networks that used different specifications and implementations（方法） to communicate with each other. They realized that needed

7、 to move away from proprietary networking systems. 体验到了80年代中期，这些公司开始经历由于他们扩张网络所带来的不断的麻烦。采用不同的规范和实现的网络不能够相互通信。他们认识到，他们需要离开专用的联网系统。 Paragraph 2 通信英语 unit 3Proprietary systems are privately developed, owned, and controlled. in the computer industry, proprietary is the opposite of open. Proprietary mean

8、s that one or a small group of companies controls all usage and evolution of the technology. Open means that free usage of the technology is available to the public. Paragraph 3 专用系统是指那些被私人开发、拥有和控制的网络。在计算机行业，专用是开放的反义词。专用意味着一个公司或一小群公司完全控制着技术的使用和发展。而开放却意味着技术可为整个公众所利用。 proprietary prpraitri 专有的、私有的Priv

9、ate praivit 私人的 、私有的Opposite n. 对立面、相反的 通信英语 unit 3To address the problem of different network systems being incompatible and incapable of communicating with each other, the international Organization for Standardization (ISO) researched network schemes, such as DECnet, SNA, and TCP/IP, to find a se

10、t of rules. as a result of this research, the ISO created a network model that could help vendors create networks that would be compatible with, and interoperate with, other networks. Paragraph 4 通信英语 unit 3The ISO reference model, released in 1984, was the descriptive scheme they created. it provid

11、ed vendors with a set of standards that could enable greater compatibility and interoperability between the various type networks technologies that were produced by many companies around the world.Paragraph 5 通信英语 unit 3The OSI reference model is the primary model基本模型 for network communications. A p

12、rimary objective of the OSI reference model is to accelerate the development of future networking products联网产品. Although there are other models in existence, most network vendors网络供应商 today relate their products to the OSI reference model, especially when they want to educate users on the use of the

13、ir products. They consider it the best tool available to teach people about sending and receiving data on a network. Paragraph 6 通信英语 unit 3The OSI reference model allows you to view the network functions that occur at each layer. More importantly, the OSI reference model is a framework you can use

14、to understand how information travels throughout a network. In addition, the OSI reference model can be used to visualize how information, or data packets, travels from application programs, through a network medium, to other application programs that are located in another computer on a network, ev

15、en if the sender and the receiver have different types of network media. Paragraph 7 通信英语 unit 3In the OSI reference model, there are seven numbered编号的 layers. Each layer illustrates表示 a particular network function网络功能. This separation分离，分解 of networking functions联网功能 is called layering分层. Dividing

16、the network into these seven layers provides the following advantages:Paragraph 8 通信英语 unit 3 It breaks network communication into smaller, simpler parts that are easier to develop . It facilitates standardization of network components to allow multiple-vendor development and support. It allows diff

17、erent types of network hardware and software to communicate with each other. It prevents changes in one layer from affecting the other layers, so that they can develop more quickly. It breaks network communication into smaller parts to make learning it easier to understand. Break into 把打碎成multiple-v

18、endor 多个供应商 prevent from 阻止 它将网络分成更小的、更简单的部分，这些部分更容易发展。它简化了网络部件的标准化，允许多个供应商开发与支持。它允许不同类型的网络软件和硬件相互通信。它防止一层的变化影响其他的层次，从而使得各层更快的进行开发。它把通信部分分成更小的部分，从而更容易理解。 Paragraph 8 通信英语 unit 3Now lets take a look at each layer in the OSI reference model ,as shown in figure 3-1.通信英语 unit 3通信英语 unit 3The application

19、 layer is the OSI layer that is closest to the user. It provides network services, such as file access and printing, to the users application. It differs form the other layers in that it does not provide services to any other OSI layer, but rather, only to applications outside the OSI model. The app

20、lication layer established the availability of intended communication parters. It also synchronizes and establishes an agreement on procedures for error recovery and control of data integrity. If you want toRemember Layer 7 in as few words as possible,think of the browsers. 应用层是OSI参考模型中离用户最近的层，它为用户的

21、应用提供网络服务，比如文件访问和打印等。它与其他的层的区别在于，它不向OSI 的其他层提供服务，相反的，它仅向OSI参考模型之外提供服务，应用层使得通信双方成为可能。它还对纠错和数据整合的过程同步并达成协议。如果你想简单的用几个词记住第7层，记住浏览器即可。 Layer 7: The application Layer 通信英语 unit 3The presentation layer ensures that the information that the application layer of one system sends out is readable by the applic

22、ation layer of another system. If necessary, the presentation layer translates between multiple data formats by using a common format, this layer also is responsible for compression and encryption. If you want to think of layer 6 in as few words as possible, think of a common data format.Layer 6: Th

23、e presentation layerAs its name implies, the session layer establishes, manages, and terminates sessions between two communicating hosts. The session layer provides its services to the presentation layers and manages their data exchange. In addition to session regulation, the session layer offers pr

24、ovision for efficient data transfer, class of services, and exception reporting of session layer, presentation layer, and application layer problems, if you want to remember layer 5 in as few as possible, think of dialogues and conversations.Layer 5: The session layer通信英语 unit 3The four lower layers

25、 of the OSI model define how data is transferred across a physical wire through internetworking devices, to the desired end station, and finally to the application. Figure 2-3 summarizes the basic function of these four layers.The Lower Layers desired dizai 所请求的 Figure 2-3 （P.39）通信英语 unit 3Layer 4 :

26、The transport layerThe transport layer segments data from the sending hosts system and reassembles the data into a data stream on the receiving hosts system. the boundary between the transport layer and the session layer can be thought of as a boundary between application protocols and data-flow pro

27、tocols. Whereas the application, presentation, and session layers are concerned with application issues, the lower four layers are concerned with data transport issues.重新组装 数据流 界线, 范围 hwrz conj. 然而, 鉴于 与有关 通信英语 unit 3The transport layer attempts to provide a data transport service that shields the u

28、pper layers from transport implementation details. Specifically, such issue as how reliable transport between two hosts is accomplished in the concern of the transport layer. In providing communication service, the transport layer established, maintains, and properly terminates connection-oriented c

29、ircuits. In providing reliable service, transport error detection-and-recovery and information flow control are used. If you want to remember layer 4 in as few words as possible, think of the flow control and reliability. 传输层试图提供数据传输服务，而将传输层的实现细节对高层进行屏蔽。而将较高层的传输实现的细节方面屏蔽。尤其应该指出的是，在两个主机之间数据传送是否可靠之类的问

30、题是由传输层来考虑实现的。在提供通信服务时，传输层建立、维持和断开面向连接的电路，在提供可靠服务的方面，传输层采用了传输误码检测和恢复，以及信息流控制技术。 Shield 保护、遮蔽、屏蔽 实施; 实现 被完成 通信英语 unit 3The network layer is a complex layer that provides connectivity and path selection between host systems that might be located on geographically separated networks. If you want to reme

31、mber layer 3 in as few words as possible, think of path selection, routing, and logical addressing.Layer 3: the network layer 通信英语 unit 3The data link layer provides the transit of data across a physical link. In so doing, the data link layer is concerned with physical (as opposed to logical) addressing, network (sometimes called logical) topology, network media access, and error detection. If you want to remember layer 2 in as few words as possible, think of frames and media access control.Layer 2: the data link layer 通信英语 unit 3The physical layer defines