计算机网络体系结构外文翻译

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 community's 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 they've 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 don't 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 andDCE 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 you're 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, etc…The 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 thecommunication process of the upper layer shielding the communication transmission system details. Representatives of the Transport Protocol：TCP, UDP, SPX, etc…The 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.OSI's seven control the use of a wide range of information and other computer systems to communicate the corresponding layer. Control information contained in thesespecial 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 computerB 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 computerapplications 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 A's 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。