计算机网络体系结构 毕业论文外文翻译.doc

附录awith the new network technology and application of the continuous rapid development of the computer network should. use of becoming increasingly widespread, the role played by the increasingly important computer networks and human. more inseparable from the lives of the communitys reliance on them will keep growing. in order for computers to communicate, they must speak the same language or protocol. in the early days of networking, networks were disorganized in many ways. companies developed proprietary network technologies that had great difficulties in exchanging information with other or existing technologies; so network interconnections were very hard to build. to solve this problem, the international organization for standardization（iso）created a network model that helps vendors to create networks compatible with each other. finding the best software is not easy. a better understanding of what you need and asking the right questions makes it easier. the software should be capable of handling challenges specific to your company. if you operate multiple distribution centers, it may be beneficial to create routes with product originating from more than one depot. few software providers though, are capable of optimizing routes using multiple depots. the provider should be able to support installation of its product. make sure to clearly understand what training and software maintenance is offered. obviously, selecting the right routing/scheduling software is critically important. unfortunately, some companies are using software that may not be best suited to their operation. logistics actives with responsibility for approving the software ought to be comfortable theyve made the right decision. it is important to realize that not all routing/scheduling software is alike！there questions to ask are： which operating system is used？ how easy is the software to use？ here is a good way to tell. ask if its graphical user interface（gui）is flexible. find out about installation speed - how long does it take？ is the software able to route third party customers with your core business？ when was the software originally released and when was it last upgraded？in 1984, iso released the open systems interconnection（osi）reference model, which is a well-defined set of specifications that ensures greater compatibility among various technologies. in fact, osi is a description of network communication that everyone refers to. it is not the only network model, but it has become the primary model for network communication. you will see further in this chapter, that the tcp/ip model is only a reduced version of the osi model. the osi model consists of seven layers, each illustrating a particular network function. meanwhile, asp continues to evolve. with the arrival of the millennium came the arrival of asp version 3. 0. version 3. 0 was released along with internet information server（iis）version 5. 0 as part of the highly anticipated microsoft windows 2000. by far, the most important new feature of version 3. 0 is the addition of a seventh, intrinsic object called asp error which should greatly simplify error handling. other new features include the addition of three new methods to the server object, and two new methods to both the application object and the session object. when programmers design an image editor for example, they dont have to think about adding osi layer 7 capabilities to that software, because it has no need for communication with other computers. on the other hand, when creating an ftp client, they must add communication capabilities to that software. at layer 7 we usually find telnet, ftp, http, smtp, snmp, or ssh. when we say, for example, layer 7 filtering, we refer to filtering application data, regardless of what port or computer it may come from. osi will be a computer network architecture（architecture）is divided into the following seven：the first layer：physical layer（physical layer）, provides communications equipment for the mechanical, electrical and functional characteristics and process for the establishment, maintenance and removal of the physical link connection. specifically, the provisions of the mechanical properties required for network connectivity connector dimensions, pin number and order situation, etc. ;the provisions of the electrical characteristics of the physical connection in the bit stream transmission line signal level of the size, impedance matching , transfer rate from the constraints; features refers to the distribution of the various signals to the exact meaning of the signal, that is the definition of the dte and dce function between the various lines; order characteristics of the definition of the use of bit stream signal transmission lines for a group of rules refers to the physical connection of the establishment, maintenance, exchange of information, dte and dce on the circuit on double-action series. in this layer, data units known as bits（bit）. belong to the typical definition of the physical layer specification included： eia / tia rs-232, eia / tia rs-449, v. 35, rj-45 and so on. the second layer： data link layer（data link layer）： in the physical layer bit stream to provide services based on adjacent node between the data link, through the provision of error control data frame（frame）in the channel error-free transmission, and the action of the series circuit. data link layer in the physical media is not reliable to provide reliable transmission. the role of this layer include： addressing the physical address, data framing, flow control, data error, such as re-issued. in this layer, data units known as the frame（frame）. data link layer protocol, including representatives of： sdlc, hdlc, ppp, stp, such as frame relay. the third layer is the network layerin the computer network to communicate between two computers may be a lot of data link may also go through a lot of communication subnet. network layer of the task is to choose a suitable inter-network routing and switching nodes, to ensure timely delivery of data. network layer will provide the data link layer packet frame components, including network layer in the package header, which contains the logical address information - - the source site and destination site address of the network address. if youre talking about an ip address, then you are in dealing with the problem of layer 3, which is “data packets”, rather than layer 2 of the “frame. ” ip is layer 3 part of the problem, in addition to a number of routing protocols and arp（arp）. all things related to routing in layer 3 processing. address resolution and routing is an important objective of level 3. network layer can also achieve congestion control features such as internet interconnection. in this layer, data packets as the unit（packet）. representatives of the network layer protocol, including: ip, ipx, rip, ospf, etcthe fourth tier is the transport layer process information. at fourth floor unit, also known as data packets（packets）. however, when you talk about tcp protocol, such as concrete and specific when the name, tcp data unit known as paragraph（segments）and the udp protocol data unit referred to as “datagram（data grams）”. this layer is responsible for obtaining all the information, therefore, it must be tracking data cell debris, out-of-order packets arrive in the transfer process and other possible risk. no. 4 for the upper layer to provide end-to-end（the end-user to end-users）of a transparent and reliable data transmission services. transparent by means of transmission is transmitted in the communication process of the upper layer shielding the communication transmission system details. representatives of the transport protocol： tcp, udp, spx, etcthe fifth layer is the session layerthis layer can also be known as the dialogue meeting between layers or layer, in the session layer and above the high-level, the data transmission is no longer the other named units, known collectively as the message. session layer does not participate in specific transmission, it provides, including access to authentication and session management, including the establishment and maintenance of mechanisms for communication between applications. if the server to verify user login is completed by the session layer. the sixth layer is presentation layerthe main solution to support this level of information that the problem of syntax. for the exchange of data will be suitable for a user from the abstract syntax, into a system suitable for the use of osi transfer syntax. to provide formatting and conversion of that data services. data compression and decompression, encryption and decryption so that the layers are responsible for. the seventh layer application layer, application layer for the operating system, applications or network services access the network interface. agreement on behalf of the application layer, including: telnet, ftp, http, snmp, etc. . through the osi layers, information from a computer software application for transfer to another application. for example, computer a on the application to send information to the computer application b, then a computer application in information need to be sent to the application layer（seventh layer）, and then this layer will be sent to that level of information（sixth floor）, indicating that the data layer will be transferred to the session layer（fifth layer）, and so continue until the physical layer（first layer）. in the physical layer, data is placed in the physical network media and sent to computer b. the physical layer of computer b to receive data from the physical media, and then send information up to data link layer（second layer）, data link layer and then to the network layer, until the information in order to arrive at the application layer of computer b. finally, the application layer of computer b and then the application information to the receiving end, thus completing the communication process. the following describes the icons in the process. osis seven control the use of a wide range of information and other computer systems to communicate the corresponding layer. control information contained in these special requests, and show that they correspond to the osi layer exchange. data at every level of the head and tail to bring the two basic forms of control information. for one to send down from the previous data, additional control information in the front as the head, attached to the back of the end of the control information is called. however, data from one level to increase the agreement and the agreement the end of the first of a osi layer is not necessary. when the data transmission between each floor, each level in the data can be added to the head and tail, and these data have been included to increase the level of the head and tail. agreement includes the first layer and the communication of information between layers. head and tail as well as the data is associated with the concept, they depend on the analysis of the protocol layer module. for example, the transport layer header includes only the transport layer can be seen the information, the transport layer of the other layers below this only the first part of a data transmission. for the network layer, an information unit from the third layer composed of the first and data. the data link layer, network layer by passing down all the information that is the first and third data layer is seen as data. in other words, a given osi layer, the information unit that contains the data from all parts of the upper head and tail, as well as data, referred to as packaging. for example, if computer a to a certain application data sent to computer b, the first data sent to the application layer. a computer in the application layer protocol data to add up and the application layer of computer b communications. formed by the first information unit includes an agreement, data, and possibly the end of the agreement was sent to that layer, that layer of computer b and then add that layer of the control information to understand the agreement first. information on the size of units in each level in agreement with the agreement the end of the first and add the increase in the first of these agreements and agreements contained in the computer b the end of the corresponding layers of control information to be used. in the physical layer, the entire information unit through the network transmission medium. computer b in the physical layer unit of information received and sent to the data link layer; and b data link layer in computer a to read the data link layer protocol header added to the control of information; and then remove the agreement and the end of the first agreement, sent to the remainder of the network layer. perform the same at every level of action： from the corresponding first layer to read the agreement and protocol tail, and remove, and then send the remaining first floor. end of application-layer implementation of these actions, the data sent to computer b on the application, the data and computer applications a is exactly the same as sent. an osi layer and another layer of communication between the second layer is the use of the services completed. services provided by adjacent layers help a osi layer with another layer corresponds to the computer system to communicate. a particular layer of the osi model is often associated with three other osi layers contact: with the layer directly adjacent to and under the floor, as well as the objectives of the corresponding computer systems networking layer. for example, computer as data link layer should be with the network layer, physical layer of computer b, as well as the data link layer communication. 附录b为了让电脑来沟通，就必须讲同样的语言或议定书。在早期的网络化，网络松散，在很多方面。公司开发了专有的网络技术，有很大的困难，交流信息与其他的或现有的技术，使网络互连非常辛苦建立的。为了解决这个问题，国际标准化组织（iso）建立了一个网络模型，可以帮助制造商网络彼此兼容。发现最佳的软件不容易。对什么的更好的理解您需要并且问合适的问题使它更加容易。软件应该是能处理挑战具体对您的公司。如果您操作多个分配中心，它也许是有利创造路线与产品起源于超过一个集中处。少量软件提供者虽则，是能优选路线使用多个集中处。提供者应该能支持它的产品的设施。保证清楚地了解什么训练和软件维护被提供。明显地，选择正确的发送预定的软件重要地重要。不幸地，一些公司使用不能是适合对他们的操作的软件。最大限制的对批准软件的责任应该是舒适的他们做出了正确的决定。它重要意识到没有所有发送预定的软件是假象！其它问题要求是： 哪个操作系统被使用？ 多么容易软件使用？ 这一个好方式知道。问如果它的图形用户界面（gui）是灵活的。发现关于设施速度- 多长时间需要？ 软件能寻址第三方顾客以您的核心业务吗？ 何时软件最初被发布了并且何时这是为时被升级？在1984年，国际标准化组织公布的开放系统互连（osi）以参考模型，这是一个清楚界定的一套技术规范，保证了更大的兼容性，各方面的技术。事实上，在osi的是一个描述网络通信的每个人都指。它并非是唯一的网络模型，但它已成为主要模式，为网络通信。你会看到进一步在这一章中，认为tcp / ip的模式只是一种降低版本的osi模型。osi模型共分七层，每个说明某一特定的网络功能。表示层的目的定义了数据代表的数据格式。数据格式通常是象ascii、jpeg、gif、tiff、mpeg等等开放系统互连层6的标准格式也定义了加密作为表示层服务。定义数据格式的the重要性是显然的。例如，当送电子邮件时，您通常送它纯文本（ascii）或html。如果接受应用不知道这些数据格式，您的电子邮件不会恰当地被显示。osi层数6为上部开放系统互连层（应用）提供一项服务。它格式化在间网络有些将被送的数据接受应用能了解并且/或者操作。如，编程人员在设计图像编辑器软件时，就无需将应用层功能添加到该软件中，因为该软件工作时无需与其它计算机进行通信。但在创建ftp客户端程序时，就必须在该软件中加入通信功能。应用层协议一般有telnet、 ftp、 http、smtp、snmp和ssh等。应用层过滤一般只是指过滤应用数据，而与数据来源的端口和主机无关。osi将计算机网络体系结构（architecture）划分为以下七层：第一层：物理层（physical layer）规定通信设备的机械的、电气的、功能的和过程的特性，用以建立、维护和拆除物理链路连接。具体地讲，机械特性规定了网络连接时所需接插件的规格尺寸、引脚数量和排列情况等；电气特性规定了在物理连接上传输bit流时线路上信号电平的大小、阻抗匹配、传输速率距离限制等；功能特性是指对各个信号先分配确切的信号含义，即定义了dte和dce之间各个线路的功能；规程特性定义了利用信号线进行bit流传输的一组操作规程，是指在物理连接的建立、维护、交换信息是，dte和dce双放在各电路上的动作系列。在这一层，数据的单位称为比特（bit）。属于物理层定义的典型规范代表包括：eia/tia rs-232、eia/tia rs-449、v.35、rj-45等。第二层：数据链路层（data link layer）在物理层提供比特流服务的基础上，建立相邻结点之间的数据链路，通过差错控制提供数据帧（frame）在信道上无差错的传输，并进行各电路上的动作系列。数据链路层在不可靠的物理介质上提供可靠的传输。该层的作用包括：物理地址寻址、数据的成帧、流量控制、数据的检错、重发等。在这一层，数据的单位称为帧（frame）。数据链路层协议的代表包括：sdlc、hdlc、ppp、stp、帧中继等。第三层：网络层在计算机网络中进行通信的两个计算机之间可能会经过很多个数据链路，也可能还要经过很多通信子网。网络层的任务就是选择合适的网间路由和交换结点，确保数据及时传送。网络层将数据链路层提供的帧组成数据包，包中封装有网络层包头，其中含有逻辑地址信息- -源站点和目的站点地址的网络地址。如果你在谈论一个ip地址，那么你是在处理第3层的问题，这是“数据包”问题，而不是第2层的“帧”。ip是第3层问题的一部分，此外还有一些路由协议和地址解析协议（arp）。有关路由的一切事情都在第3层处理。地址解析和路由是3层的重要目的。网络层还可以实现拥塞控制、网际互连等功能。在这一层，数据的单位称为数据包（packet）。网络层协议的代表包括：ip、ipx、rip、ospf等。第四层：是处理信息的传输层第4层的数据单元也称作数据包（packets）。但是，当你谈论tcp等具体的协议时又有特殊的叫法，tcp的数据单元称为段（segments）而udp协议的数据单元称为“数据报（datagrams）”。这个层负责获取全部信息，因此，