计算机网络体系结构外文翻译

附录A

With 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 and