网络工程专业外文翻译--计算机网络

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网工英语

计算机网络－局域网（中英文对照）[Local area data networks，normally referred to simply as local area networks or LANs，are used to interconnect distributed communities of computer-based DTEs located within a single building or localized group of buildings.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.Alternatively，it may be used to interconnect computer-based equipment distributed around a factory or hospital complex[1].Since all the equipment is located within a single establishment，however，LANs are normally installed and maintained by the organization.Hence they are also referred to as private data networks.The main difference between a communication path established using a LAN and a connection made through a public data network is that a LAN normally offers much higher data transmission rates because of the relatively short physical separations involved[2].In the context of the ISO Reference Model for OSI，however，this difference manifests itself only at the lower network dependent layers.In many instances the higher protocol layers in the reference model are the same for both types of network.Before describing the structure and operation of the different types of LAN，it is perhaps helpful to first identify some of the selection issues that must be considered.A summary of some of the these issues is given in Fig. 14-5.It should be stressed that this is only a summary;there are also many possible links between the tips of the branches associated with the figure[3].1.TopologyMost wide area networks，such as the PSTN，use a mesh(sometimes referred to as anetwork)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, which is a variation of the bus and ring[4].This is shown in Fig. 14-6，sometimes it is called hub/tree topology.2.Transmission mediaTwisted pair，coaxial cable and optical fiber 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.They arecarrier-sense-multiple-access with collision detection(CSMA/CD)，for bus network topologies，and control token，for use with either bus or ring networks[5].CSMA / CD is used to control multiple-access networks.Each on the network“listens” before attempting to send a message，waiting for the“traffic”to clear[6].If two stations try to send their messages at exactly the same time，a“collision”is detected，an both stations are required to“step back”and try later.Control token is another way of controlling access to a shared transmission medium that is by the use of a control(pertnission)token.This token is passed from one DTE to another according to a defined set of rules understood and adhered to by all DTEs connected to the medium.A DTE may only transmit a frame when it is in possession of the token and，after it has transmined the frame，it passes the token on to allow another DTE to access the tranamission medium.NOTES[1] computer-based是指由计算机控制的，或装有微处理器的。

计算机网络介绍中英文

计算机网络介绍中英文计算机网络基础介绍（英文）AD：Introduction to Computer NetworkComputer network is a system connecting two or more computers. A computer network allows user to exchange data quickly, access and share resources including equipments, application software, and information.Data communications systems are the electronic systems that transmit data over communications lines from one location to another. You might use data communications through your microcomputer to send information to a friend using another computer. You might work for an organization whose computer system is spread throughout a building, or even throughout the country or world. That is, all the parts—input and output units, processor, and storage devices—are in different places and linked by communications. Or you might use telecommunications lines—telephone lines—to tap into information located in an outside data bank. You could then transmit it to your microcomputer for your own reworking and analysis.To attach to a network, a special-purpose hardware component is used to handle all the transmission. The hardware is called a network adapter card or network interface card (NIC), it is a printed circuit board plugged into a computer's bus, and a cable connects it to a network medium.Communications networks differ in geographical size. There are three important types: LANs, MANs, and WANs.Local Area Networks Networks with computers andperipheral devices in close physical proximity—within the same building, for instance—are called local area networks (LANs). Linked by cable-telephone, coaxial, or fiber optic. LANs often use a bus form organization. In a LAN, people can share different equipments, which lower the cost of equipments. LAN may be linked to other LANs or to larger networks by using a network gateway. With the gateway, one LAN may be connected to the LAN of another LAN of another office group. It may also be connected to others in the wide world, even if their configurations are different. Alternatively, a network bridge would be used to connect networks with the same configurations.There is a newly development for LANs: WLAN. A wireless LAN (WLAN) is a flexible data communication system implemented as an extension to, or as an alternative for, a wired LAN within a building or campus. Using electromagnetic waves, WLANs transmit and receive data over the air, minimizing the need for wired connections. Thus, WLANs combine data connectivity with user mobility, and, through simplified configuration, enable movable LANs.Over the recent several years, WLANs have gained strong popularity in a number of vertical markets, including the health-care, retail, manufacturing, warehousing, and academic arenas.These industries have profited from the productivity gains of using hand-held terminals and notebook computers to transmit real-time information to centralized hosts for processing. Today WLANs are becoming more widely recognized as a general-purpose connectivity alternative for a broad range of business customers.Applications for Wireless LANs Wireless LANs frequently augment rather than replace wired LAN networks—oftenproviding the final few meters of connectivity between a backbone network and the mobile user. The following list describes some of the many applications made possible through the power and flexibility of wireless LANs:●Doctors and nurses in hospitals are more productive because hand-held or notebook computers with wireless LAN capability deliver patient information instantly.●Consulting or accounting audit engagement teams or small workgroups increase productivity with quick network setup.●Network managers in dynamic environments minimize the overhead of moves, adds, and changes with wireless LANs, thereby reducing the cost of LAN ownership.●Training sites at corporations and students at universities use wireless connectivity to facilitate access to information, information exchanges, and learning.●Network managers installing networked computers in older buildings find that wireless LANs are a cost-effective network infrastructure solution.●Retail store owners use wireless networks to simply frequent network reconfiguration.●Trade show and branch office workers minimize setup requirements by installing preconfigured wireless LANs needing no local MIS support.●Warehouse workers use wireless LANs to exchange information with central databases and increase their productivity.●Network managers implement wireless LANs to provide backup for mission-critical applications running on wired networks.●Senior executives in conference rooms make quickerdecisions because they have real-time information at their fingertips.The increasingly mobile user also becomes a clear candidate for a wireless LAN. Portable access to wireless networks can be achieved using laptop computers and wireless NICs. This enables the user to travel to various locations–meeting rooms, hallways, lobbies, cafeterias, classrooms, etc.–and still have access to their networked data. Without wireless access, the user would have to carry clumsy cabling and find a network tap to plug into.Metropolitan Area Networks These networks are used as links between office buildings in a city. Cellular phone systems expand the flexibility of MAN by allowing links to car phones and portable phones.Wide Area Networks Wide area networks are countrywide and worldwide networks. Among other kinds of channels, they use microwave relays and satellites to reach users over long distances. One of the most widely used WANs is Internet, which allows users to connect to other users and facilities worldwide.计算机网络基础介绍（译文）计算机网络是连接两个或多个计算机的系统，它允许用户快速地交换数据，访问和共享包括设备、应用软件和信息在内的资源。

计算机网络词汇翻译浅析

计算机网络词汇翻译浅析计算机网络已经成为现代社会中不可或缺的一部分，它使得人们可以在世界各地进行信息交流和数据传输。

在进行计算机网络翻译时，我们需要深入理解各种网络术语的含义和用法。

在本文中，我将就一些常见的计算机网络词汇进行浅析，并提供它们的翻译建议。

1. Internet英文原意：a global computer network providing a variety of information and communication facilities翻译建议：互联网解析：互联网是指连接在一起的全球计算机网络系统，提供各种信息和通信服务。

2. Network英文原意：a group or system of interconnected people or things 翻译建议：网络解析：网络是指相互连接在一起的一组或系统，可以包括计算机、设备和人。

3. Router英文原意：a device that forwards data packets between computer networks翻译建议：路由器解析：路由器是一种设备，用于在不同的计算机网络之间转发数据包。

它通常用于将数据从一个网络发送到另一个网络。

4. Ethernet英文原意：a system for connecting a number of computer systems to form a local area network翻译建议：以太网解析：以太网是一种将多台计算机系统连接在一起形成局域网的系统。

5. Firewall英文原意：a network security system that monitors and controls incoming and outgoing network traffic翻译建议：防火墙解析：防火墙是一种网络安全系统，用于监控和控制进出网络的流量。

6. Server英文原意：a computer or computer program that manages access to a centralized resource or service翻译建议：服务器解析：服务器是一台计算机或计算机程序，用于管理对集中资源或服务的访问。

Computer network中英文对照简介

Computer network计算机网络A computer network is a group of more computers connected to each electronically. This means that the computers can "talk" to each other and that every computer in the network can send information to the others. Usually, this means that the speed of the connection is fast - faster than a normal connection to the Internet.计算机网络是一组多台计算机连接到每个电子。

这意味着计算机可以“讲”给对方，并且每一个在网络上的计算机可以将信息发送到其他。

通常情况下，这意味着连接速度快 - 速度比正常的连接到互联网。

Some basic types of computer networks include:▪ A local area network (often called a LAN) connects two or more computers, and may be called a corporate network in an office or business setting.▪An "internetwork", sometimes called a Wide Area Network (because of the wide distance between networks) connects two or more smaller networks together. The largest internetwork is called the Internet.计算机网络的一些基本类型包括：局域网络（通常被称为一个LAN）连接两个或更多的计算机，并可能被称为一个企业网络，在办公室或业务设置。

计算机类网站网络建设外文翻译、中英文翻译、外文文献翻译

外文翻译Birth of the NetThe Internet has had a relatively brief, but explosive history so far. It grew out of an experiment begun in the 1960's by the U.S. Department of Defense. The DoD wanted to create a computer network that would continue to function in the event of a disaster, such as a nuclear war. If part of the network were damaged or destroyed, the rest of the system still had to work. That network was ARPANET, which linked U.S. scientific and academic researchers. It was the forerunner of today's Internet.In 1985, the National Science Foundation (NSF) created NSFNET, a series of networks for research and education communication. Based on ARPANET protocols, the NSFNET created a national backbone service, provided free to any U.S. research and educational institution. At the same time, regional networks were created to link individual institutions with the national backbone service.NSFNET grew rapidly as people discovered its potential, and as new software applications were created to make access easier. Corporations such as Sprint and MCI began to build their own networks, which they linked to NSFNET. As commercial firms and other regional network providers have taken over the operation of the major Internet arteries, NSF has withdrawn from the backbone business.NSF also coordinated a service called InterNIC, which registered all addresses on the Internet so that data could be routed to the right system. This service has now been taken over by Network Solutions, Inc., in cooperation with NSF.How the Web WorksThe World Wide Web, the graphical portion of the Internet, is the most popular part of the Internet by far. Once you spend time on the Web,you will begin to feel like there is no limit to what you can discover. The Web allows rich and diverse communication by displaying text, graphics, animation, photos, sound and video.So just what is this miraculous creation? The Web physically consists of your personal computer, web browser software, a connection to an Internet service provider, computers called servers that host digital data and routers and switches to direct the flow of information.The Web is known as a client-server system. Your computer is the client; the remote computers that store electronic files are the servers. Here's how it works:Let's say you want to pay a visit to the the Louvre museum website. First you enter the address or URL of the website in your web browser (more about this shortly). Then your browser requests the web page from the web server that hosts the Louvre's site. The Louvre's server sends the data over the Internet to your computer. Your web browser interprets the data, displaying it on your computer screen.The Louvre's website also has links to the sites of other museums, such as the Vatican Museum. When you click your mouse on a link, you access the web server for the Vatican Museum.The "glue" that holds the Web together is called hypertext and hyperlinks. This feature allow electronic files on the Web to be linked so you can easily jump between them. On the Web, you navigate through pages of information based on what interests you at that particular moment, commonly known as browsing or surfing the Net.To access the Web you need web browser software, such as Netscape Navigator or Microsoft Internet Explorer. How does your web browser distinguish between web pages and other files on the Internet? Web pages are written in a computer language called Hypertext Markup Language or HTML.Some Web HistoryThe World Wide Web (WWW) was originally developed in 1990 at CERN, the European Laboratory for Particle Physics. It is now managed by The World Wide Web Consortium, also known as the World Wide Web Initiative.The WWW Consortium is funded by a large number of corporate members, including AT&T, Adobe Systems, Inc., Microsoft Corporation and Sun Microsystems, Inc. Its purpose is to promote the growth of the Web by developing technical specifications and reference software that will be freely available to everyone. The Consortium is run by MIT with INRIA (The French National Institute for Research in Computer Science) acting as European host, in collaboration with CERN.The National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign, was instrumental in the development of early graphical software utilizing the World Wide Web features created by CERN. NCSA focuses on improving the productivity of researchers by providing software for scientific modeling, analysis, and visualization. The World Wide Web was an obvious way to fulfill that mission. NCSA Mosaic, one of the earliest web browsers, was distributed free to the public. It led directly to the phenomenal growth of the World Wide Web.Understanding Web AddressesYou can think of the World Wide Web as a network of electronic files stored on computers all around the world. Hypertext links these resources together. Uniform Resource Locators or URLs are the addresses used to locate thesefiles. The information contained in a URL gives you the ability to jump from one web page to another with just a click of your mouse. When you type a URL into your browser or click on a hypertext link, your browser is sending a request to a remote computer to download a file.What does a typical URL look like? Here are some examples:/The home page for study english.ftp:///pub/A directory of files at MIT* available for downloading.news:rec.gardens.rosesA newsgroup on rose gardening.The first part of a URL (before the two slashes* tells you the type of resource or method of access at that address. For example:∙http - a hypertext document or directory∙gopher - a gopher document or menu∙ftp - a file available for downloading or a directory of such files∙news - a newsgroup∙telnet - a computer system that you can log into over the Internet∙WAIS* - a database or document in a Wide Area Information Search database∙file - a file located on a local drive (your hard drive)The second part is typically the address of the computer where the data or service is located. Additional parts may specify the names of files, the port to connect to, or the text to search for in a database.You can enter the URL of a site by typing it into the Location bar of your web browser, just under the toolbar.Most browsers record URLs that you want to use again, by adding them to a special menu. In Netscape Navigator, it's called Bookmarks. In Microsoft Explorer, it's called Favorites. Once you add a URL to your list, you can return to that web page simply by clicking on the name in your list, instead of retyping the entire URL.Most of the URLs you will be using start with http which stands for Hypertext Transfer Protocol*. http is the method by which HTML files are transferred over the Web. Here are some other important things to know about URLs:∙ A URL usually has no spaces.∙ A URL always uses forward slashes (//).If you enter a URL incorrectly, your browser will not be able to locate the site or resource you want. Should you get an error message or the wrong site, make sure you typed the address correctly.You can find the URL behind any link by passing your mouse cursor over the link. The pointer will turn into a hand and the URL will appear in the browser's status ba r, usually located at the bottom of your screen.Domain NamesWhen you think of the Internet, you probably think of ".com." Just what do those three letters at the end of a World Wide Web address mean?Every computer that hosts data on the Internet has a unique numerical address. For example, the numerical address for the White House is198.137.240.100. But since few people want to remember long strings of numbers, the Domain Name System (DNS)* was developed. DNS, a critical part of the Internet's technical infrastructure*, correlates* a numerical address to a word. To access the White House website, you could type its number into the address box of your web browser. But most people prefer to use "." In this case, the domain name is . In general, the three-letter domain name suffix* is known as a generictop-level domai n and describes the type of organization. In the last few years, the lines have somewhat blurred* between these categories..com - business (commercial).edu - educational.org - non-profit.mil - military.net - network provider.gov - governmentA domain name always has two or more parts separated by dots and typically consists of some form of an organization's name and the three-letter suffix. For example, the domain name for IBM is ""; the United Nations is "."If a domain name is available, and provided it does not infringe* on an existing trademark, anyone can register the name for $35 a year through Network Solutions, Inc., which is authorized to register .com, .net and .org domains. You can use the box below to see if a name is a available. Don't be surprised ifthe .com name you want is already taken, however. Of the over 8 million domain names, 85% are .com domains.ICANN, the Internet Corporation for Assigned Names and Numbers, manages the Domain Name System. As of this writing, there are plans to add additional top-level domains, such as .web and .store. When that will actually happen is anybody's guess.To check for, or register a domain name, type it into the search box.It should take this form: In addition to the generic top-level domains, 244 national top-level domains were established for countries and territories*, for example:.au - Australia.ca - Canada.fr - France.de - Germany.uk - United KingdomFor US $275 per name, you can also register an international domain name with Net Names. Be aware that some countries have restrictions for registering names.If you plan to register your own domain name, whether it's a .com or not, keep these tips in mind:The shorter the name, the better. (But it should reflect your family name, interest or business.)The name should be easy to remember.It should be easy to type without making mistakes.Remember, the Internet is global. Ideally, a domain name will "read" in a language other than English.Telephone lines were designed to carry the human voice, not electronic data from a computer. Modems were invented to convert digital computer signals into a form that allows them to travel over the phone lines. Those are the scratchy sounds you hear from a modem's speaker. A modem on theother end of the line can understand it and convert the sounds back into digital information that the computer can understand. By the way, the word modem stands for MOdulator/DEModulator.Buying and using a modem used to be relatively easy. Not too long ago, almost all modems transferred data at a rate of 2400 Bps (bits per second). Today, modems not only run faster, they are also loaded with features like error control and data compression. So, in addition to converting and interpreting signals, modems also act like traffic cops, monitoring and regulating the flow of information. That way, one computer doesn't send information until the receiving computer is ready for it. Each of these features, modulation, error control, and data compression, requires a separate kind of protocol and that's what some of those terms you see like V.32, V.32bis, V.42bis and MNP5 refer to.If your computer didn't come with an internal modem, consider buying an external one, because it is much easier to install and operate. For example, when your modem gets stuck (not an unusual occurrence), you need to turn it off and on to get it working properly. With an internal modem, that means restarting your computer--a waste of time. With an external modem it's as easy as flipping a switch.Here's a tip for you: in most areas, if you have Call Waiting, you can disable it by inserting *70 in front of the number you dial to connect to the Internet (or any online service). This will prevent an incoming call from accidentally kicking you off the line.This table illustrates the relative difference in data transmission speeds for different types of files. A modem's speed is measured in bits per second (bps). A 14.4 modem sends data at 14,400 bits per second. A 28.8 modem is twice as fast, sending and receiving data at a rate of 28,800 bits per second.Until nearly the end of 1995, the conventional wisdom was that 28.8 Kbps was about the fastest speed you could squeeze out of a regular copper telephoneline. Today, you can buy 33.6 Kbps modems, and modems that are capable of 56 Kbps. The key question for you, is knowing what speed modems your Internet service provider (ISP) has. If your ISP has only 28.8 Kbps modems on its end of the line, you could have the fastest modem in the world, and only be able to connect at 28.8 Kbps. Before you invest in a 33.6 Kbps or a 56 Kbps modem, make sure your ISP supports them.Speed It UpThere are faster ways to transmit data by using an ISDN or leased line. In many parts of the U.S., phone companies are offering home ISDN at less than $30 a month. ISDN requires a so-called ISDN adapter instead of a modem, and a phone line with a special connection that allows it to send and receive digital signals. You have to arrange with your phone company to have this equipment installed. For more about ISDN, visit Dan Kegel's ISDN Page.An ISDN line has a data transfer rate of between 57,600 bits per second and 128,000 bits per second, which is at least double the rate of a 28.8 Kbps modem. Leased lines come in two configurations: T1 and T3. A T1 line offers a data transfer rate of 1.54 million bits per second. Unlike ISDN, a T-1 line is a dedicated connection, meaning that it is permanently connected to the Internet. This is useful for web servers or other computers that need to be connected to the Internet all the time. It is possible to lease only a portion of a T-1 line using one of two systems: fractional T-1 or Frame Relay. You can lease them in blocks ranging from 128 Kbps to 1.5 Mbps. The differences are not worth going into in detail, but fractional T-1 will be more expensive at the slower available speeds and Frame Relay will be slightly more expensive as you approach the full T-1 speed of 1.5 Mbps. A T-3 line is significantly faster, at 45 million bits per second. The backbone of the Internet consists of T-3 lines. Leased lines are very expensive and are generally only used by companies whose business is built around the Internet or need to transfer massiveamounts of data. ISDN, on the other hand, is available in some cities for a very reasonable price. Not all phone companies offer residential ISDN service. Check with your local phone company for availability in your area.Cable ModemsA relatively new development is a device that provides high-speed Internet access via a cable TV network. With speeds of up to 36 Mbps, cable modems can download data in seconds that might take fifty times longer with a dial-up connection. Because it works with your TV cable, it doesn't tie up a telephone line. Best of all, it's always on, so there is no need to connect--no more busy signals! This service is now available in some cities in the United States and Europe.The download times in the table above are relative and are meant to give you a general idea of how long it would take to download different sized files at different connection speeds, under the best of circumstances. Many things can interfere with the speed of your file transfer. These can range from excessive line noise on your telephone line and the speed of the web server from which you are downloading files, to the number of other people who are simultaneously trying to access the same file or other files in the same directory.DSLDSL (Digital Subscriber Line) is another high-speed technology that is becoming increasingly popular. DSL lines are always connected to the Internet, so you don't need to dial-up. Typically, data can be transferred at rates up to 1.544 Mbps downstream and about 128 Kbps upstream over ordinary telephone lines. Since a DSL line carries both voice and data, you don't have to install another phone line. You can use your existing line to establish DSLservice, provided service is available in your area and you are within the specified distance from the telephone company's central switching office.DSL service requires a special modem. Prices for equipment, DSL installation and monthly service can vary considerably, so check with your local phone company and Internet service provider. The good news is that prices are coming down as competition heats up.Anatomy of a Web PageA web page is an electronic document written in a computer language called HTML, short for Hypertext Markup Language. Each web page has a unique address, called a URL* or Uniform Resource Locator, which identifies its location on the network.A website has one or more related web pages, depending on how it's designed. Web pages on a site are linked together through a system of hyperlinks* , enabling you to jump between them by clicking on a link. On the Web, you navigate through pages of information according to your interests.Home Sweet Home PageWhen you browse the World Wide Web you'll see the term home page often. Think of a home page as the starting point of a website. Like the table of contents of a book or magazine, the home page usually provides an overview of what you'll find at the website. A site can have one page, many pages or a few long ones, depending on how it's designed. If there isn't a lot of information, the home page may be the only page. But usually you will find at least a few other pages.Web pages vary wildly in design and content, but most use a traditional magazine format. At the top of the page is a masthead* or banner graphic*, then a list of items, such as articles, often with a brief description. The items in the list usually link to other pages on the website, or to other sites. Sometimes these links are highlighted* words in the body of the text, or are arranged in a list, like an index. They can also be a combination* of both. A web page can also have images that link to other content.How can you tell which text are links? Text links appear in a different color from the rest of the text--typically in blue and underlined. When you move yourcursor over a text link or over a graphic link, it will change from an arrow to a hand. The hypertext words often hint* at what you will link to.When you return to a page with a link you've already visited, the hypertext words will often be in a different color, so you know you've already been there. But you can certainly go there again. Don't be surprised though, if the next time you visit a site, the page looks different and the information has changed. The Web is a dynamic* medium. To encourage visitors to return to a site, some web publishers change pages often. That's what makes browsing the Web so excitingA Home (Page) of Your OwnIn the 60s, people asked about your astrological* sign. In the 90s, they want to know your URL. These days, having a web address is almost as important as a street address. Your website is an electronic meeting place for your family, friends and potentially*, millions of people around the world. Building your digital domain can be easier than you may think. Best of all, you may not have to spend a cent. The Web brims with all kinds of free services, from tools to help you build your site, to free graphics, animation and site hosting. All it takes is some time and creativity.Think of your home page as the starting point of your website. Like the table of contents of a book or magazine, the home page is the front door. Your site can have one or more pages, depending on how you design it. If there isn't a lot of information just yet, your site will most likely have only a home page. But the site is sure to grow over time.While web pages vary dramatically* in their design and content, most use a traditional magazine layout. At the top of the page is a banner graphic. Next comes a greeting and a short description of the site. Pictures, text, and links to other websites follow.If the site has more than one page, there's typically a list of items--similar to an index--often with a brief description. The items in the list link to other pages on the website. Sometimes these links are highlighted words in the body of the text. It can also be a combination of both. Additionally, a web page may have images that link to other content.Before you start building your site, do some planning. Think about whom the site is for and what you want to say. Next, gather up the material that you wantto put on the site: write the copy, scan the photos, design or find the graphics. Draw a rough layout on a sheet of paper.While there are no rules you have to follow, there are a few things to keep in mind:∙Start simply. If you are too ambitious at the beginning, you may never get the site off the ground. You can always add to your site.∙Less is better. Most people don't like to read a lot of text online. Break it into small chunks.∙Use restraint. Although you can use wild colors and images for the background of your pages, make sure your visitors will be able to readthe text easily.∙Smaller is better. Most people connect to the Internet with a modem.Since it can take a long time to download large image files, keep the file sizes small.∙Have the rights. Don't put any material on your site unless you are sure you can do it legally. Read Learn the Net's copyright article for moreabout this.Stake Your ClaimNow it's time to roll up your sleeves and start building. Learn the Net Communities provides tools to help you build your site, free web hosting, and a community of other homesteaders.Your Internet service provider may include free web hosting services with an account, one alternative to consider.Decoding Error MessagesAs you surf the Net, you will undoubtedly find that at times you can't access certain websites. Why, you make wonder? Error messages attempt to explain the reason. Unfortunately, these cryptic* messages baffle* most people.We've deciphered* the most common ones you may encounter.400 - Bad RequestProblem: There's something wrong with the address you entered. You may not be authorized* to access the web page, or maybe it no longer exists.Solution: Check the address carefully, especially if the address is long. Make sure that the slashes are correct (they should be forward slashes) and that all the names are properly spelled. Web addresses are case sensitive, socheck that the names are capitalized in your entry as they are in the original reference to the website.401 - UnauthorizedProblem: You can't access a website, because you're not on the guest list, your password is invalid or you have entered your password incorrectly.Solution: If you think you have authorization, try typing your password again. Remember that passwords are case sensitive.403 - ForbiddenProblem: Essentially the same as a 401.Solution: Try entering your password again or move on to another site.404 - Not FoundProblem: Either the web page no longer exists on the server or it is nowhere to be found.Solution: Check the address carefully and try entering it again. You might also see if the site has a search engine and if so, use it to hunt for the document. (It's not uncommon for pages to change their addresses when a website is redesigned.) To get to the home page of the site, delete everything after the domain name and hit the Enter or Return key.503 - Service unavailableProblem: Your Internet service provider (ISP) or your company's Internet connection may be down.Solution: Take a stretch, wait a few minutes and try again. If you still have no luck, phone your ISP or system administrator.Bad file requestProblem: Your web browser may not be able to decipher the online form you want to access. There may also be a technical error in the form.Solution: Consider sending a message to the site's webmaster, providing any technical information you can, such as the browser and version you use.Connection refused by hostProblem: You don't have permission to access the page or your password is incorrect.Solution: Try typing your password again if you think you should have access.Failed DNS lookupProblem: DNS stands for the Domain Name System, which is the system that looks up the name of a website, finds a corresponding number (similar to a phone number), then directs your request to the appropriate web server on theInternet. When the lookup fails, the host server can't be located.Solution: Try clicking on the Reload or Refresh button on your browser toolbar. If this doesn't work, check the address and enter it again. If all else fails, try again later.File contains no dataProblem: The site has no web pages on it.Solution: Check the address and enter it again. If you get the same error message, try again later.Host unavailableProblem: The web server is down.Solution: Try clicking on the Reload or Refresh button. If this doesn't work, try again later.Host unknownProblem: The web server is down, the site may have moved, or you've been disconnected from the Net.Solution: Try clicking on the Reload or Refresh button and check to see that you are still online. If this fails, try using a search engine to find the site. It may have a new address.Network connection refused by the serverProblem: The web server is busy.Solution: Try again in a while.Unable to locate hostProblem: The web server is down or you've been disconnected from the Net.Solution: Try clicking on the Reload or Refresh button and check to see that you are still online.Unable to locate serverProblem: The web server is out-of-business or you may have entered the address incorrectly.Solution: Check the address and try typing it again.Web BrowsersA web browser is the software program you use to access the World Wide Web, the graphical portion of the Internet. The first browser, called NCSA Mosaic, was developed at the National Center for Supercomputing Applications in the early '90s. The easy-to-use point-and-click interface*helped popularize the Web, although few then could imagine the explosive growth that would soon occur.Although many different browsers are available, Microsoft Internet Explorer* and Netscape Navigator* are the two most popular ones. Netscape and Microsoft have put so much money into their browsers that the competition can't keep up. The pitched battle* between the two companies to dominate* the market has lead to continual improvements to the software. Version 4.0 and later releases of either browser are excellent choices. (By the way, both are based on NCSA Mosaic.) You can download Explorer and Navigator for free from each company's website. If you have one browser already, you can test out the other. Also note that there are slight differences between the Windows and MacIntosh* versions.You can surf to your heart's content, but it's easy to get lost in this electronic web. That's where your browser can really help. Browsers come loaded with all sorts of handy features. Fortunately, you can learn the basics in just a few minutes, then take the time to explore the advanced functions.Both Explorer and Navigator have more similarities than differences, so we'll primarily cover those. For the most up-to-date information about the browsers, and a complete tutorial, check the online handbook under the Help menu or go to the websites of the respective* software companies.Browser AnatomyWhen you first launch your web browser, usually by double-clicking on the icon on your desktop, a predefined web page, your home page, will appear. With Netscape Navigator for instance, you will be taken to Netscape's NetCenter.The Toolbar （工具栏）The row of buttons at the top of your web browser, known as the toolbar, helps you travel through the web of possibilities, even keeping track ofwhere you've been. Since the toolbars for Navigator and Explorer differ slightly, we'll first describe what the buttons in common do:o The Back button returns you the previous page you've visited.o Use the Forward button to return to the page you just came from.o Home takes you to whichever home page you've chosen. (If you haven't selected one, it will return you to the default home page,usually the Microsoft or Netscape website.)。

网络工程师常用英文单词和缩写翻译

ARPARNET(Internet) ：阿帕网ICCC ：国际计算机通信会议CCITT ：国际电报电话咨询委员会SNA ：系统网络体系结构(IBM)DNA ：数字网络体系结构(DEC)CSMA/CD ：载波监听多路访问/冲突检测(Xerox) NGI ：下一代INTERNETInternet2 ：第二代INTERNETTCP/IP SNA SPX/IPX AppleTalk ：网络协议NII ：国家信息基础设施(信息高速公路)GII ：全球信息基础设施MIPS ：PC的处理能力Petabit ：10^15BIT/SCu芯片: ：铜OC48 ：光缆通信SDH ：同步数字复用WDH ：波分复用ADSL ：不对称数字用户服务线HFE/HFC：结构和Cable-modem 机顶盒PCS ：便携式智能终端CODEC ：编码解码器ASK(amplitude shift keying) ：幅移键控法FSK(frequency shift keying) ：频移键控法PSK(phase shift keying) ：相移键控法NRZ (Non return to zero) ：不归零制PCM(pulse code modulation) ：脉冲代码调制nonlinear encoding ：非线性编程FDM ：频分多路复用TDM ：时分多路复用STDM ：统计时分多路复用DS0 ：64kb/sDS1 ：24DS0DS1C ：48DS0DS2 ：96DS0DS3 ：762DS0DS4 ：4032DS0CSU(channel service unit) ：信道服务部件SONET/SDH ：同步光纤网络接口LRC ：纵向冗余校验CRC ：循环冗余校验ARQ ：自动重发请求ACK ：确认NAK ：不确认preamble ：前文postamble ：后文ITU ：国际电信联合会character-oriented ：面向字符bit-oriented ：面向位SYNC ：同步字符HDLC ：面向位的方案SDLC ：面向位的方案bit-stuffing ：位插入STP ：屏蔽双绞线UTP ：非屏蔽双绞线RG-58A/U ：标准RG-11 ：用于10BASE5RG-59U ：75欧0.25INCH CATVRG-62U ：9欧0.25INCH ARCnet10BASE5 ：IEEE802.3RG-59U ：0.25inch CATVRG-62U ：0.25inch ARCnetLED(light emitting diobe) ：发光二级管ILD(injection laster diobe) ：注入型激光二级管PIN ：检波器APD ：检波器intensity modulation ：亮度调制line of sight ：可视通路CCITT V.28(EIA RS232C) ：非平衡型CCITT V.10/X.26(EIA RS423A) ：新的非平衡型CCITT V.11/X.27(EIA RS422A) ：新的平衡型TD ：发送数据RD ：接收数据XON/XOFF ：流控制Automatic Repeat Request Protocol ：自动重发请求Send and wait ARQ:continuous ：ARQ停等ARQ Ward Christensen ：人名Kermit ：协议circuit switching ：线路交换packet switching ：分组交换virtual circuit ：虚电路ATM(asynchronous transfer mode) ：异步传输模式ATDM ：异步时分多路复用packetizer ：打包器VPI(vritual path identifier) ：虚路径标识VCI(virtual channel identifier) ：虚通道标识syntax ：语法semantics ：语义timing ：定时OSI(open system interconnection) ：开放系统session ：会话synchronization ：同步activity management ：活动管理AE ：应用实体UE ：用户元素CASE ：公共应用服务元素SASE ：特定应用服务元素VT ：虚拟终端JIM ：作业传送和操作reverved ：保留echo ：回送discard ：丢弃active users ：活动用户daytime ：白天netstat(who is up of NETSTAT)qotd(quote of the day)日期引用chargen(character generator)字符发送器nameserver(domani name server)域名服务器bootps(bootstrap protocol server/client)引导协议服务器/客户机tftp(trivial file transfer)简单文件传送sunrpc(sun microsystems RPC)SUN公司NTP:network time protocol网络时间协议SNMP(SNMP net monitor)SNMP网络监控器SNMP traps陷井biffunix comsatdaemone.g timed daemonsyslogsystem logURG紧急字段可用ACK确认字段可用请求急迫操作RST连接复位SYN同步序号FIN发送方字节流结束Manchester曼彻斯特编码FDDI(fiber distributed data interface)光纤分布数据接口TTRT目标标记循环时间aggregation of multiple link segments多重链接分段聚合协议MAN(metropolitan area network plus)城域网CSMA/CD(carrier sense multiple access/collision detection) 载波监听Token bus令牌总线Token ring令牌环SAP服务访问点request indictaion response confirmationLLC PDULLC协议数据单元DSAP address目地服务访问点地址字段SSAP address源服务访问点地址字段XID交换标识SABME置扩充的异步平衡方式DISC断开连接DM断开FRMR帧拒收solt timeAUI连接单元接口MAU介质连接接口MDI介质相关接口PMA物理介质接口SFD起始定界符PAD填充字段FCS帧校验序列PLS物理层收发信号slot time时间Inter Frame Gap 帧attempt limit最大重传次数back off limit避免算法参数Jam size阻塞参数max frame size最大帧address size地址collaspsed backone 折叠式主干网BSS基本服务集ESS扩展服务集DFW-MAC分布式基础无线MAC IFS帧间空隙SIFS:短PIFSDIFS分布协调CTS发送清除DQDB(IEEE802.6)分布式队列双总线TDM时分复用TMS多时分交换TSI时间片互换TST网络机构TSSST STS SSTSS TSTST网络机构PSTN公用交换电话网public switched telephone network详细PBX:private branch exchange专用交换网PABX;private automatic branch exchange自动交换机CBX:computerized branch exchange程控交换SLIP:serial line IP串行IPLCP(link control protocol)链路控制协议NCP:network control protocol网络控制协议BRI基本速率接口PRI群速率接口LAPB:line access protocol balanced链路访问协议平衡registration登录interrupt中断LAP F link access procedure for frame-mode bearer serivesrotate不知道recovery恢复discard丢弃retransmission重传switched access交换访问intergated access集成访问alerting警告progress进展AALATM适配层GFC总流控cell rate decoupling信元率去耦SDH同步数字级PDH准国步数字级GSM:group special mobile移动通讯NSS网络子系统OMC-R操作维护中心BSS基站子系统BSC基站控制器BTS基站收发信机MS移动站SIM:subscriber identity module 标识模块MSCHLR归属位置寄存器VLR访问位置寄存器AUC鉴权中心EIR设备识别寄存器OMC-S操作维护中心SC短消息中心WAP无线应用协议WAE无线应用层WSP会话层WTP事务层WTLS安全层WDP传输层MAP移动应用部分WML无线标记语言SSL:secure sockets layer安全套接层PCS个人通信业务PCN个人通信网GEO对地静止轨道NON-GE0(MEO,LEO)不清楚ITU国际电信联盟VSAT:very small aperture -terminal 甚小天线终端LEOS低轨道卫星通信系统中继器bridge网桥router路由器gateway网关ONsemble stackable 10BASE可叠加组合型集线器transparent bridge传输桥source routing bridge源路径桥broadcast storm广播风暴encapsulation封装translation bridging转换桥接方式SRT源地址选择透明桥offset偏移more flag标识ICMPINTERNET控制报文协议SPF:shortest path first最短路径IGP:interior gateway protocol核心网关协议EGP:exterior gateway protocol 扩展网关协议RIP:routing information protocol 路由信息协议OSPF开放最短径优先协议acquisition request获取请求acquisition confirm获取确认cease中止poll轮询IPX/SPX internetwork packet exchange/sequented packet exchange NOVELLinterpreter解释器redirector重定向器SFT system fault tolerant系统容错ELS entry level solution不认识ODI开放数据链路接口NDIS network device interface specification网络设备接口...DDCS数据库管理和分布数据库连接服务DCE:distributed computing environment分布计算环境OSF:open software foundation开放软件基金PWS:peer web serviceWEB服务器OEM原始设备制造商RAS远程访问服务IIS:Internet Information serverINTERNET信息服务WINS:windows internet name systemWINDOWS命名服务NTDS:windows NT directory serverNT目录服务TDI传输驱动程序接口schedule++应用程序,预约本COSE:common open software environment普通开放软件环境RPC远程过程调用SNMP:simple network management protocol简单网管协议SMI:structer of management information管理信息结构SMT:station management管理站SMTP:simple mail transfer protocol简单邮件传输协议SNA:system network architectureIBM网络SNR:signal noise ratio信噪比SONENT:synchronous optical network同步光纤网络SPE:synchronous payload envelope同步PAYLOAD信CMIS/CMIP公共管理信息服务/协议CMISE公共管理信息服务agent代理IMT:inductive modeling technology不知道plaintext明文ciphertext脱密encryption加密decryption解密symmetric key cryptography对称加密asymmetric key cryptography不对称加密public key公钥private key私钥DES:data encryption standard数据加密标准IDEA:international data encryption algorithm 国际加密算法PIN:personal identification number个人标识符session key会话层密钥KDC:key distribuetion center密钥分发中心sign签名seal封装certificate证书certificate authority CA证书权威机构OSF开放软件中心AFS:andrew file system分布式文件系统ticket凭证authenticatior身份认证timestamp时间标记reply attack检测重放攻击realm域PKI公钥基础设施certificate hierarchy证书层次结构across certificate交叉证书security domain安全领域cerfificate revoke list(CRL)证书层次结构LDAP:light weight directory access protocol 协议access matrix访问矩阵ACL:access control list访问列表reference monitor引用监控器course grained粗粒度访问控制medium grained中粒度访问控制fine grained细粒度访问控制CORBA面向对象的分布系统应用MQ报文队列VPN虚拟专网IPSEC:IP security安全IPSA:security association安全??encopulation security payload封装安全负载AH:authentication header鉴别报头IKE:Internet key exchange交换rogue programs捣乱程序IPSP:IP security protocol安全IKMP:internet key managemetn protocol 协议IESGInternet工程领导小组SHA安全散列算法MAC:message authentication code代码CBC密码块链接SSL安全套接层协议cerfificate verify证书检验报文PEM私用强化邮件PGP:pretty good privacy好的private保密authenticated已认证SEPP安全电子付费协议SET安全电子交易middleware中间件GSS-API通用安全服务SNP安全网络编程BWD:browser web database浏览WEBplugin插入件basic authentication scheme不知道digest authentication scheme摘要认证方法open group:the open group research institute研究所DCE:distributed computing environment分布式计算机环境SLP:secure local proxy安全局部代理SDG:secure domain proxy安全域代理OMG:object management group目标管理组CORBS:common object request broker architecture 不清楚authentication鉴别access control访问控制data confidnetiality保密data integrity数据完整性non-reputation防止否认enciphermant加密机制digital signature mechanisms数据完整性authentication mechanisms路由控制机制notarization mechanisms公证trusted function可信security labels安全标记event dectection事件检测security audit trail安全审计跟踪security recovery安全恢复TCSEC:trusted computer system evaluation criteria标准TCSEC TNI:trusted network interpretation of the TCSEC 标准TCSEC TDI:trusted database interpretation of the TCSEC 标准ITSEC:information technology security evaluation标准CC:command criteria for IT security evaluation安全classified criteria for secruity protection中国安全of computer information system中国安全GB17859-1999国标TCB:trusted computing baseSNMP:simple network management protocol网管ICMP:internet control message protocol互联网控制信息协议ARP:address resolution protocol地址解析协议TCP:transmission control protocol传输控制协议UDP:user datagram protocol用户数据报协议SMTP:simple mail transfer protocol简单邮件传输DNS:domain name service服务器NSP:name service protocol服务器TElnet:telcommunication networkTELEGP:exterior gateway protocol外部网关连接器协议IGP:inter gateway protocol内部网关连接器协议SLIP串行接口协议PPP点对点协议UNICAST单播地址cluster群集地址multicast组播地址scable model可伸缩模型integrated model集成模型OLAP联机分析工具NAS:network applications supportDEC公司的工具NWC:newwave computingHP工具OCCA:open cooperative computing architecture 开放合作计算体系结构DAA:distributed application architectureDG的分布应用体系结构COSE:common opensystem enviroment通用开放系统环境CDE:common desktop enviroment通用桌面环境DCE分布式计算环境RPC远程过程调用DME分布管理环境OSE/APP开放系统环境应用可移植框架ODA开放文件体系结构ODL开放文件语言。

计算机网络中英文对照外文翻译文献

中英文资料外文翻译计算机网络计算机网络，通常简单的被称作是一种网络，是一家集电脑和设备为一体的沟通渠道，便于用户之间的沟通交流和资源共享。

网络可以根据其多种特点来分类。

计算机网络允许资源和信息在互联设备中共享。

一．历史早期的计算机网络通信始于20世纪50年代末，包括军事雷达系统、半自动地面防空系统及其相关的商业航空订票系统、半自动商业研究环境。

1957年俄罗斯向太空发射人造卫星。

十八个月后，美国开始设立高级研究计划局(ARPA)并第一次发射人造卫星。

然后用阿帕网上的另外一台计算机分享了这个信息。

这一切的负责者是美国博士莱德里尔克。

阿帕网于来于自印度，1969年印度将其名字改为因特网。

上世纪60年代，高级研究计划局(ARPA)开始为美国国防部资助并设计高级研究计划局网(阿帕网)。

因特网的发展始于1969年，20世纪60年代起开始在此基础上设计开发，由此，阿帕网演变成现代互联网。

二．目的计算机网络可以被用于各种用途:为通信提供便利:使用网络，人们很容易通过电子邮件、即时信息、聊天室、电话、视频电话和视频会议来进行沟通和交流。

共享硬件:在网络环境下，每台计算机可以获取和使用网络硬件资源，例如打印一份文件可以通过网络打印机。

共享文件：数据和信息: 在网络环境中，授权用户可以访问存储在其他计算机上的网络数据和信息。

提供进入数据和信息共享存储设备的能力是许多网络的一个重要特征。

共享软件:用户可以连接到远程计算机的网络应用程序。

信息保存。

安全保证。

三．网络分类下面的列表显示用于网络分类：3．1连接方式计算机网络可以据硬件和软件技术分为用来连接个人设备的网络，如：光纤、局域网、无线局域网、家用网络设备、电缆通讯和G.hn（有线家庭网络标准）等等。

以太网的定义，它是由IEEE 802标准，并利用各种媒介，使设备之间进行通信的网络。

经常部署的设备包括网络集线器、交换机、网桥、路由器。

无线局域网技术是使用无线设备进行连接的。

网络工程专业外文翻译--网络

外文原文：The NetWorksBirth of the NetThe Internet has had a relatively brief, but explosive history so far. It grew out of an experiment begun in the 1960's by the U.S. Department of Defense. The DoD wanted to create a computer network that would continue to function in the event of a disaster, such as a nuclear war. If part of the network were damaged or destroyed, the rest of the system still had to work. That network was ARPANET, which linked U.S. scientific and academic researchers. It was the forerunner of today's Internet.In 1985, the National Science Foundation (NSF) created NSFNET, a series of networks for research and education communication. Based on ARPANET protocols, the NSFNET created a national backbone service, provided free to any U.S. research and educational institution. At the same time, regional networks were created to link individual institutions with the national backbone service.NSFNET grew rapidly as people discovered its potential, and as new software applications were created to make access easier. Corporations such as Sprint and MCI began to build their own networks, which they linked to NSFNET. As commercial firms and other regional network providers have taken over the operation of the major Internet arteries, NSF has withdrawn from the backbone business.NSF also coordinated a service called InterNIC, which registered all addresses on the Internet so that data could be routed to the right system. This service has now been taken over by Network Solutions, Inc., in cooperation with NSF.How the Web WorksThe World Wide Web, the graphical portion of the Internet, is the most popular part of the Internet by far. Once you spend time on the Web,you will begin to feel like there is no limit to what you can discover. The Web allows rich and diverse communication by displaying text, graphics, animation, photos, sound and video.So just what is this miraculous creation? The Web physically consists of your personal computer, web browser software, a connection to an Internet service provider, computers called servers that host digital data and routers and switches to direct the flow of information.The Web is known as a client-server system. Your computer is the client; the remote computers that store electronic files are the servers. Here's how it works:Let's say you want to pay a visit to the the Louvre museum website. First you enter the address or URL of the website in your web browser (more about this shortly). Then your browserrequests the web page from the web server that hosts the Louvre's site. The Louvre's server sends the data over the Internet to your computer. Your web browser interprets the data, displaying it on your computer screen.The Louvre's website also has links to the sites of other museums, such as the Vatican Museum. When you click your mouse on a link, you access the web server for the Vatican Museum.The "glue" that holds the Web together is called hypertext and hyperlinks. This feature allow electronic files on the Web to be linked so you can easily jump between them. On the Web, you navigate through pages of information based on what interests you at that particular moment, commonly known as browsing or surfing the Net.To access the Web you need web browser software, such as Netscape Navigator or Microsoft Internet Explorer. How does your web browser distinguish between web pages and other files on the Internet? Web pages are written in a computer language called Hypertext Markup Language or HTML.Some Web HistoryThe World Wide Web (WWW) was originally developed in 1990 at CERN, the European Laboratory for Particle Physics. It is now managed by The World Wide Web Consortium, also known as the World Wide Web Initiative.The WWW Consortium is funded by a large number of corporate members, including AT&T, Adobe Systems, Inc., Microsoft Corporation and Sun Microsystems, Inc. Its purpose is to promote the growth of the Web by developing technical specifications and reference software that will be freely available to everyone. The Consortium is run by MIT with INRIA (The French National Institute for Research in Computer Science) acting as European host, in collaboration with CERN.The National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign, was instrumental in the development of early graphical software utilizing the World Wide Web features created by CERN. NCSA focuses on improving the productivity of researchers by providing software for scientific modeling, analysis, and visualization. The World Wide Web was an obvious way to fulfill that mission. NCSA Mosaic, one of the earliest web browsers, was distributed free to the public. It led directly to the phenomenal growth of the World Wide Web.Understanding Web AddressesYou can think of the World Wide Web as a network of electronic files stored on computers all around the world. Hypertext links these resources together. Uniform Resource Locators or URLs are the addresses used to locate these files. The information contained in a URL gives you the ability to jump from one web page to another with just a click of your mouse. When you type aURL into your browser or click on a hypertext link, your browser is sending a request to a remote computer to download a file.What does a typical URL look like? Here are some examples:/The home page for study english.ftp:///pub/A directory of files at MIT* available for downloading.news:rec.gardens.rosesA newsgroup on rose gardening.The first part of a URL (before the two slashes* tells you the type of resource or method of access at that address. For example:·http - a hypertext document or directory·gopher - a gopher document or menu·ftp - a file available for downloading or a directory of such files·news - a newsgroup·telnet - a computer system that you can log into over the Internet·WAIS* - a database or document in a Wide Area Information Search database·file - a file located on a local drive (your hard drive)The second part is typically the address of the computer where the data or service is located. Additional parts may specify the names of files, the port to connect to, or the text to search for in a database.You can enter the URL of a site by typing it into the Location bar of your web browser, just under the toolbar.Most browsers record URLs that you want to use again, by adding them to a special menu. In Netscape Navigator, it's called Bookmarks. In Microsoft Explorer, it's called Favorites. Once you add a URL to your list, you can return to that web page simply by clicking on the name in your list, instead of retyping the entire URL.Most of the URLs you will be using start with http which stands for Hypertext Transfer Protocol*. http is the method by which HTML files are transferred over the Web. Here are some other important things to know about URLs:· A URL usually has no spaces.· A URL always uses forward slashes (//).If you enter a URL incorrectly, your browser will not be able to locate the site or resource you want. Should you get an error message or the wrong site, make sure you typed the address correctly.You can find the URL behind any link by passing your mouse cursor over the link. The pointer will turn into a hand and the URL will appear in the browser's status bar, usually located at the bottom of your screen.Domain NamesWhen you think of the Internet, you probably think of ".com." Just what do those three letters at the end of a World Wide Web address mean?Every computer that hosts data on the Internet has a unique numerical address. For example, the numerical address for the White House is 198.137.240.100. But since few people want to remember long strings of numbers, the Domain Name System (DNS)* was developed. DNS, a critical part of the Internet's technical infrastructure*, correlates* a numerical address to a word. To access the White House website, you could type its number into the address box of your web browser. But most people prefer to use "." In this case, the domain name is .In general, the three-letter domain name suffix* is known as a generic top-level domain and describes the type of organization. In the last few years, the lines have somewhat blurred* between these categories..com - business (commercial).edu - educational.org - non-profit.mil - military.net - network provider.gov - governmentA domain name always has two or more parts separated by dots and typically consists of some form of an organization's name and the three-letter suffix. For example, the domain name for IBM is ""; the United Nations is "."If a domain name is available, and provided it does not infringe* on an existing trademark, anyone can register the name for $35 a year through Network Solutions, Inc., which is authorized to register .com, .net and .org domains. You can use the box below to see if a name is a available. Don't be surprised if the .com name you want is already taken, however. Of the over 8 million domain names, 85% are .com domains.ICANN, the Internet Corporation for Assigned Names and Numbers, manages the Domain Name System. As of this writing, there are plans to add additional top-level domains, such as .web and .store. When that will actually happen is anybody's guess.To check for, or register a domain name, type it into the search box.It should take this form: In addition to the generic top-level domains, 244 national top-level domains were established for countries and territories*, for example:.au - Australia.ca - Canada.fr - France.de - Germany.uk - United KingdomFor US $275 per name, you can also register an international domain name with Net Names. Be aware that some countries have restrictions for registering names.If you plan to register your own domain name, whether it's a .com or not, keep these tips in mind: The shorter the name, the better. (But it should reflect your family name, interest or business.) The name should be easy to remember.It should be easy to type without making mistakes.Remember, the Internet is global. Ideally, a domain name will "read" in a language other than English.About ModemTelephone lines were designed to carry the human voice, not electronic data from a computer. Modems were invented to convert digital computer signals into a form that allows them to travel over the phone lines. Those are the scratchy sounds you hear from a modem's speaker. A modem on the other end of the line can understand it and convert the sounds back into digital information that the computer can understand. By the way, the word modem stands for MOdulator/DEModulator.Buying and using a modem used to be relatively easy. Not too long ago, almost all modems transferred data at a rate of 2400 Bps (bits per second). Today, modems not only run faster, they are also loaded with features like error control and data compression. So, in addition to converting and interpreting signals, modems also act like traffic cops, monitoring and regulating the flow of information. That way, one computer doesn't send information until the receiving computer is ready for it. Each of these features, modulation, error control, and data compression, requires a separate kind of protocol and that's what some of those terms you see like V.32, V.32bis, V.42bis and MNP5 refer to.If your computer didn't come with an internal modem, consider buying an external one, because it is much easier to install and operate. For example, when your modem gets stuck (not an unusual occurrence), you need to turn it off and on to get it working properly. With an internal modem, that means restarting your computer--a waste of time. With an external modem it's as easy as flipping a switch.Here's a tip for you: in most areas, if you have Call Waiting, you can disable it by inserting *70 in front of the number you dial to connect to the Internet (or any online service). This will prevent an incoming call from accidentally kicking you off the line.This table illustrates the relative difference in data transmission speeds for different types of files. A modem's speed is measured in bits per second (bps). A 14.4 modem sends data at 14,400 bits per second. A 28.8 modem is twice as fast, sending and receiving data at a rate of 28,800 bits per second.Until nearly the end of 1995, the conventional wisdom was that 28.8 Kbps was about the fastest speed you could squeeze out of a regular copper telephone line. Today, you can buy 33.6 Kbps modems, and modems that are capable of 56 Kbps. The key question for you, is knowing what speed modems your Internet service provider (ISP) has. If your ISP has only 28.8 Kbps modems on its end of the line, you could have the fastest modem in the world, and only be able to connect at 28.8 Kbps. Before you invest in a 33.6 Kbps or a 56 Kbps modem, make sure your ISP supports them.Speed It UpThere are faster ways to transmit data by using an ISDN or leased line. In many parts of the U.S., phone companies are offering home ISDN at less than $30 a month. ISDN requires a so-called ISDN adapter instead of a modem, and a phone line with a special connection that allows it to send and receive digital signals. You have to arrange with your phone company to have this equipment installed. For more about ISDN, visit Dan Kegel's ISDN Page.An ISDN line has a data transfer rate of between 57,600 bits per second and 128,000 bits per second, which is at least double the rate of a 28.8 Kbps modem. Leased lines come in two configurations: T1 and T3. A T1 line offers a data transfer rate of 1.54 million bits per second. Unlike ISDN, a T-1 line is a dedicated connection, meaning that it is permanently connected to the Internet. This is useful for web servers or other computers that need to be connected to the Internet all the time. It is possible to lease only a portion of a T-1 line using one of two systems: fractional T-1 or Frame Relay. You can lease them in blocks ranging from 128 Kbps to 1.5 Mbps. The differences are not worth going into in detail, but fractional T-1 will be more expensive at the slower available speeds and Frame Relay will be slightly more expensive as you approach the full T-1 speed of 1.5 Mbps. A T-3 line is significantly faster, at 45 million bits per second. The backbone of the Internet consists of T-3 lines.Leased lines are very expensive and are generally only used by companies whose business is built around the Internet or need to transfer massive amounts of data. ISDN, on the other hand, is available in some cities for a very reasonable price. Not all phone companies offer residential ISDN service. Check with your local phone company for availability in your area.Cable ModemsA relatively new development is a device that provides high-speed Internet access via a cable TV network. With speeds of up to 36 Mbps, cable modems can download data in seconds that might take fifty times longer with a dial-up connection. Because it works with your TV cable, it doesn't tie up a telephone line. Best of all, it's always on, so there is no need to connect--no more busy signals! This service is now available in some cities in the United States and Europe.The download times in the table above are relative and are meant to give you a general idea of how long it would take to download different sized files at different connection speeds, under the best of circumstances. Many things can interfere with the speed of your file transfer. These can range from excessive line noise on your telephone line and the speed of the web server from which you are downloading files, to the number of other people who are simultaneously trying to access the same file or other files in the same directory.DSLDSL (Digital Subscriber Line) is another high-speed technology that is becoming increasingly popular. DSL lines are always connected to the Internet, so you don't need to dial-up. Typically, data can be transferred at rates up to 1.544 Mbps downstream and about 128 Kbps upstream over ordinary telephone lines. Since a DSL line carries both voice and data, you don't have to install another phone line. You can use your existing line to establish DSL service, provided service is available in your area and you are within the specified distance from the telephone company's central switching office.DSL service requires a special modem. Prices for equipment, DSL installation and monthly service can vary considerably, so check with your local phone company and Internet service provider. The good news is that prices are coming down as competition heats up.WebsitesAnatomy of a Web PageA web page is an electronic document written in a computer language called HTML, short for Hypertext Markup Language. Each web page has a unique address, called a URL* or Uniform Resource Locator, which identifies its location on the network.A website has one or more related web pages, depending on how it's designed. Web pages on a site are linked together through a system of hyperlinks* , enabling you to jump between them by clicking on a link. On the Web, you navigate through pages of information according to your interests.Home Sweet Home PageWhen you browse the World Wide Web you'll see the term home page often. Think of a homepage as the starting point of a website. Like the table of contents of a book or magazine, the home page usually provides an overview of what you'll find at the website. A site can have one page, many pages or a few long ones, depending on how it's designed. If there isn't a lot of information, the home page may be the only page. But usually you will find at least a few other pages.Web pages vary wildly in design and content, but most use a traditional magazine format. At the top of the page is a masthead* or banner graphic*, then a list of items, such as articles, often with a brief description. The items in the list usually link to other pages on the website, or to other sites. Sometimes these links are highlighted* words in the body of the text, or are arranged in a list, like an index. They can also be a combination* of both. A web page can also have images that link to other content.How can you tell which text are links? Text links appear in a different color from the rest of the text--typically in blue and underlined. When you move your cursor over a text link or over a graphic link, it will change from an arrow to a hand. The hypertext words often hint* at what you will link to.When you return to a page with a link you've already visited, the hypertext words will often be in a different color, so you know you've already been there. But you can certainly go there again. Don't be surprised though, if the next time you visit a site, the page looks different and the information has changed. The Web is a dynamic* medium. To encourage visitors to return to a site, some web publishers change pages often. That's what makes browsing the Web so excitingA Home (Page) of Your OwnIn the 60s, people asked about your astrological* sign. In the 90s, they want to know your URL. These days, having a web address is almost as important as a street address. Your website is an electronic meeting place for your family, friends and potentially*, millions of people around the world. Building your digital domain can be easier than you may think. Best of all, you may not have to spend a cent. The Web brims with all kinds of free services, from tools to help you build your site, to free graphics, animation and site hosting. All it takes is some time and creativity. Think of your home page as the starting point of your website. Like the table of contents of a book or magazine, the home page is the front door. Your site can have one or more pages, depending on how you design it. If there isn't a lot of information just yet, your site will most likely have only a home page. But the site is sure to grow over time.While web pages vary dramatically* in their design and content, most use a traditional magazine layout. At the top of the page is a banner graphic. Next comes a greeting and a short description of the site. Pictures, text, and links to other websites follow.If the site has more than one page, there's typically a list of items--similar to an index--often with a brief description. The items in the list link to other pages on the website. Sometimes these linksare highlighted words in the body of the text. It can also be a combination of both. Additionally, a web page may have images that link to other content.Before you start building your site, do some planning. Think about whom the site is for and what you want to say. Next, gather up the material that you want to put on the site: write the copy, scan the photos, design or find the graphics. Draw a rough layout on a sheet of paper.While there are no rules you have to follow, there are a few things to keep in mind:·Start simply. If you are too ambitious at the beginning, you may never get the site off the ground. You can always add to your site.·Less is better. Most people don't like to read a lot of text online. Break it into small chunks. ·Use restraint. Although you can use wild colors and images for the background of your pages, make sure your visitors will be able to read the text easily.·Smaller is better. Most people connect to the Internet with a modem. Since it can take a long time to download large image files, keep the file sizes small.·Have the rights. Don't put any material on your site unless you are sure you can do it legally. Read Learn the Net's copyright article for more about this.Stake Your ClaimNow it's time to roll up your sleeves and start building. Learn the Net Communities provides tools to help you build your site, free web hosting, and a community of other homesteaders.Your Internet service provider may include free web hosting services with an account, one alternative to consider.Decoding Error MessagesAs you surf the Net, you will undoubtedly find that at times you can't access certain websites. Why, you make wonder? Error messages attempt to explain the reason. Unfortunately, these cryptic* messages baffle* most people. We've deciphered* the most common ones you may encounter.400 - Bad RequestProblem: There's something wrong with the address you entered. You may not be authorized* to access the web page, or maybe it no longer exists.Solution: Check the address carefully, especially if the address is long. Make sure that the slashes are correct (they should be forward slashes) and that all the names are properly spelled. Web addresses are case sensitive, so check that the names are capitalized in your entry as they are in the original reference to the website.401 - UnauthorizedProblem: You can't access a website, because you're not on the guest list, your password is invalid or you have entered your password incorrectly.Solution: If you think you have authorization, try typing your password again. Remember that passwords are case sensitive.403 - ForbiddenProblem: Essentially the same as a 401.Solution: Try entering your password again or move on to another site.404 - Not FoundProblem: Either the web page no longer exists on the server or it is nowhere to be found.Solution: Check the address carefully and try entering it again. You might also see if the site has a search engine and if so, use it to hunt for the document. (It's not uncommon for pages to change their addresses when a website is redesigned.) To get to the home page of the site, delete everything after the domain name and hit the Enter or Return key.503 - Service unavailableProblem: Your Internet service provider (ISP) or your company's Internet connection may be down.Solution: Take a stretch, wait a few minutes and try again. If you still have no luck, phone your ISP or system administrator.Bad file requestProblem: Your web browser may not be able to decipher the online form you want to access. There may also be a technical error in the form.Solution: Consider sending a message to the site's webmaster, providing any technical information you can, such as the browser and version you use.Connection refused by hostProblem: You don't have permission to access the page or your password is incorrect.Solution: Try typing your password again if you think you should have access.Failed DNS lookupProblem: DNS stands for the Domain Name System, which is the system that looks up the name of a website, finds a corresponding number (similar to a phone number), then directs your request to the appropriate web server on the Internet. When the lookup fails, the host server can't be located.Solution: Try clicking on the Reload or Refresh button on your browser toolbar. If this doesn't work, check the address and enter it again. If all else fails, try again later.File contains no dataProblem: The site has no web pages on it.Solution: Check the address and enter it again. If you get the same error message, try again later.Host unavailableProblem: The web server is down.Solution: Try clicking on the Reload or Refresh button. If this doesn't work, try again later.Host unknownProblem: The web server is down, the site may have moved, or you've been disconnected from the Net.Solution: Try clicking on the Reload or Refresh button and check to see that you are still online. If this fails, try using a search engine to find the site. It may have a new address.Network connection refused by the serverProblem: The web server is busy.Solution: Try again in a while.Unable to locate hostProblem: The web server is down or you've been disconnected from the Net.Solution: Try clicking on the Reload or Refresh button and check to see that you are still online.Unable to locate serverProblem: The web server is out-of-business or you may have entered the address incorrectly.Solution: Check the address and try typing it again.Web BrowsersA web browser is the software program you use to access the World Wide Web, the graphical portion of the Internet. The first browser, called NCSA Mosaic, was developed at the National Center for Supercomputing Applications in the early '90s. The easy-to-use point-and-click interface* helped popularize the Web, although few then could imagine the explosive growth that would soon occur.Although many different browsers are available, Microsoft Internet Explorer* and Netscape Navigator* are the two most popular ones. Netscape and Microsoft have put so much money into their browsers that the competition can't keep up. The pitched battle* between the two companies to dominate* the market has lead to continual improvements to the software. Version 4.0 and later releases of either browser are excellent choices. (By the way, both are based on NCSA Mosaic.) You can download Explorer and Navigator for free from each company's website. If you have one browser already, you can test out the other. Also note that there are slight differences between the Windows and MacIntosh* versions.You can surf to your heart's content, but it's easy to get lost in this electronic web. That's where your browser can really help. Browsers come loaded with all sorts of handy features. Fortunately, you can learn the basics in just a few minutes, then take the time to explore the。

计算机网络专业外语PPT

What is
the Computer Network Technically, Network is defined as "If at least one process in one computer is able to send/receive data to/from at least one process residing in a remote computer, then the two computers are said to be in network".
The Applications(应用应用) 应用
A usenet newsgroup（新闻组） is
a repository usually within the Usenet system, for messages posted from many users in different locations. The term may be confusing to some, because it is usually a discussion group. Newsgroups are technically distinct from, but functionally similar to, discussion forums on the World Wide Web. News reader software is used to read newsgroups.
The Applications(应用应用) 应用
---Video conferencing
The Applications(应用应用) 应用
Voice over IP (VoIP网络电话) is a family of

网络工程专业外文翻译--PLC基础知识简介

外文原文：PLC elementary knowledge synopsisIn the automated control domain, PLC is one kind of important control device. At present, in the world has more than 200 factories to produce more than 300 varieties PLC product, applies in the automobile (23%), the grain processing (16.4%), chemistry/drugs manufacture (14.6%), the metal/mine (11.5%), the paper pulp/papermaking (11.3%) and so on the profession. In order to make fellow beginners conveniently to understand PLC, this article to the PLC development, the basic structure, the disposition, using and so on the elementary knowledge makes a synopsis.First, PLC development courseIn the industrial production process, the massive switches quantity sequential control, it carries on the smooth movement according to the logical condition, and defers to the logical relations to carry on the chain-like protection movement the control, and massive data acquisition. In the tradition, these functions are realize through air operated or the electricity control system. In 1968 American GM (general automobile) the company proposed the substitution continues the electricity control device the request, the second year, the American numeral company developed based on the integrated circuit and the electronic technology control device, used sequenced the method to apply for the first time to the electrical control, this was the first generation of programmable foreword controller, called Programmable Controller (PC).After the personal computer (is called PC) to develop, in order to be convenient, also in order to reflect the programmable controller the function characteristic, the programmable foreword controller chooses a name is Programmable Logic Controller (PLC), now, still frequently was called PLC PC.The PLC definition has many kinds. The international electrician committee (IEC) to PLC the definition is: The programmable controller is one kind of digital operation operation electronic system, specially for applies under the industry environment designs. It uses the programmable foreword the memory, uses for to carry out the logic operation, the sequential control in its internal storage, fixed time, counts with operation the and so on arithmetic operation instruction, and through digital, the simulation input and the output, controls each kind of type the machineryor the production process. The programmable foreword controller and its the related equipment, all should according to easy form a whole with the industry control system, is easy to expand its function the principle design.On the century 80's to the 90's intermediate stages, are PLC develop the quickest time, the yearly rate continuously maintenance are 30-40%. In this time, PLC in the processing simulation quantity ability, the digital operation ability, the man-machine connection ability and the networking capability obtains the large scale enhancement, PLC gradually enters the process control domain, substituted in certain applications has been at the dominant position in the process control domain the DCS system.PLC has the versatility strongly, the easy to operate, the adaption surface broad, the reliability high, the antijamming ability strong, the programming is simple and so on the characteristic. PLC in the industrial automation control specially is in the sequential control status, in future which may foresee, is unable to substitute.Second, PLC constitutionFrom the structure the minute, PLC divides into the stationary type and the combined type (module type) two kinds. Stationary PLC including the CPU board, the I/O board, demonstrated the kneading board, the memory block, the power source and so on, these element groups synthesize a not dismantable whole. Module type PLC including the CPU module, the I/O module, the memory, the power source module, the ledger wall or the rack, these modules may defer to the certain rule combination disposition. Second, PLC constitution.Third, CPU constitutionCPU is the PLC core, plays nerve center's role, every time wraps PLC at least to have CPU, it function receive and storage user program and data which entrusts with according to the PLC system program, with scanning way gathering the condition or the data which sends by the scene input device, and stores the stipulation in the register, simultaneously, diagnoses the power source and in the PLC internal circuit active status and the programming process grammatical error and so on. After enters the movement, reads from the user program memory by the strip takes the instruction, the duty which stipulated according to the instruction produces the corresponding control signal again after the analysis, directs the related control circuit.CPU mainly by the logic unit, the controller, the register and realizes the data, the control and the condition main line constitution which between them relates, the CPU unit also includes the periphery chip, the main line connection and the related electric circuit. The memory mainly uses in the stored routine and the data, is the PLCessential composition unit.Looked like in the user, nonessential multianalysis CPU internal circuit, but or should have the enough understanding to each part of work mechanism. The CPU controller controls the CPU work, reads by it takes the instruction, the interpretive order and carries out the instruction. But the work rhythm by shakes the signal control. The logic unit uses in to carry on the numeral or the logic operation, works under the controller direction. The register participation operation, coexists stores the operation the intermediate result, it also is works under the controller direction.The CPU speed and the memory capacity are the PLC important parameter, they are deciding the PLC working speed, the IO quantity and the software capacity and so on, therefore is limiting the control scale.Fourth, I/O modulePLC and the electrical return route connection, is (I/O) completes through the input output unit. The I/O module integrated the PLC I/O electric circuit, its input temporary storage device reflection input signal condition, output point reflection output latch condition. The load module transforms the electrical signal the digital signal to enter the PLC system, the output module is opposite. I/O divides into the switch quantity input (DI), switch quantity output (DO), simulation quantity input (AI), simulation quantity output (AO) and so on module.The switch quantity is refers has and closes (or 1 and 0) two kind of conditions signals, the simulation quantity is only a quantity which refers continuously changes. Commonly used I/O classifies as follows:Switch quantity: Divides equally according to the voltage water, has 220V AC, 110V AC, 24VDC, divides according to the isolation way, has the relay isolation and the transistor isolation.Simulation quantity: Divides according to the signal type, has the electric current (4-20mA,0-20mA), the voltage (0-10V,0-5V, -10-10V) and so on, divides according to the precision, has 12bit,14bit,16bit and so on.Besides above general I/O, but also has the special I/O module, like module and so on thermal resistance, thermo-element, pulse.According to the I/O points determination module specification and the quantity, the I/O module may be many may be few, but its biggest number the basic disposition ability which can manage CPU, namely biggest ledger wall or rack Key slot number limit.Fifth, power source moduleThe PLC power source uses in is the PLC various modules integrated circuit provides the work power source. At the same time, some also provides 24V for the input circuit the work power source. The mains input type includes: (What the alternating current supply (220V AC or 110V AC), the direct-current power supply is commonly used is 24V AC).Sixth, ledger wall or rackThe majority module type PLC use ledger wall or the rack, its function is: On the electricity, realizes during various modules relation, enables CPU to visit on the ledger wall all modules, on the machinery, realizes during various modules connection, enable various modules to constitute a whole.Seventh, PLC system other equipment1st, programs the equipment: The programming is the PLC development application, the monitor movement, the inspection maintains the essential component, uses in to program, makes some hypotheses to the system, monitors the system working condition which PLC and PLC controls, but it not directly participates in the scene control movement. Small programming PLC generally has the grasping programming, at present generally (movement programming software) acts as the programming by the computer.2nd, man-machine contact surface: The simplest man-machine contact surface is the indicating lamp and the button, at present the liquid crystal screen (or touches screen) a formula writing style operator terminal application to be more and more widespread, (movement configuration software) acts as the man-machine contact surface by the computer extremely to popularize.3rd, input-output device: Uses in permanently the memory user data, like EPROM, EEPROM reading in, bar code microreader, input simulation quantity potentiometer, printer and so on.Eighth, PLC correspondence networkingDepends upon the advanced industry network technology to be allowed rapidly effectively to collect, the transmission produces and manages the data. Therefore, the network is more and more remarkable in the automated system integration project importance, even some people proposed the "network is the controller" viewpoint view.PLC has the correspondence networking the function, it causes between PLC and PLC, PLC and on between the position computer and all that intelligent equipment can exchange the information, forms a unified whole, the realization dispersercommon control. Most PLC has the RS-232 connection, but also has some in sets has supports respective correspondence agreement the connection.PLC correspondence, but also the realization mutually has not been operational, IEC had stipulated the many kinds of field bus standard, the PLC various factories have the use.(Specially is center large-scale control system) says regarding an automated project, the choice network count for much. First, the network will have to be open, facilitates the different equipment the integration and the future system scale expansion; Next, in view of the different network level transmission performance requirement, the choice network form, this must in thoroughly understand this network standard the agreement, under the mechanism premise carries on; Once more, the synthesis considered system cost, equipment compatibility, scene environment serviceable and so on concrete question, determined the different level uses network standard.中文译文：PLC基础知识简介在自动化控制领域，PLC是一种重要的控制设备。

计算机网络外文文献外文翻译英文文献新技术的计算机网络

文献来源：/Freepaper/Jisuanji/wangluo/200810/28156.html一、原文New technique of the computer networkAbstractThe 21 century is an ages of the information economy, being the computer network technique of representative techniques this ages, will be at very fast speed develop soon in continuously creatively, and will go deep into the people's work, life and study. Therefore, control this technique and then seem to be more to deliver the importance. Now I mainly introduce the new technique of a few networks in actuality live of application.keywordsInternet Digital Certificates Digital Wallets Grid Storage1. ForewordInternet turns 36, still a work in progressThirty-six years after computer scientists at UCLA linked two bulky computers using a 15-foot gray cable, testing a new way for exchanging data over networks, what would ultimately become the Internet remains a work in progress.University researchers are experimenting with ways to increase its capacity and speed. Programmers are trying to imbue Web pages with intelligence. And work is underway to re-engineer the network to reduce Spam (junk mail) and security troubles.All the while threats loom: Critics warn that commercial, legal and political pressures could hinder the types of innovations that made the Internet what it is today.Stephen Crocker and Vinton Cerf were among the graduate students who joined UCLA professor Len Klein rock in an engineering lab on Sept. 2, 1969, as bits of meaningless test data flowed silently between the two computers. By January, three other "nodes" joined the fledgling network.Then came e-mail a few years later, a core communications protocol called TCP/IP in the late 70s, the domain name system in the 80s and the World Wide Web - now thesecond most popular application behind e-mail - in 1990. The Internet expanded beyond its initial military and educational domain into businesses and homes around the world.Today, Crocker continues work on the Internet, designing better tools for collaboration. And as security chairman for the Internet's key oversight body, he is trying to defend the core addressing system from outside threats.He acknowledges the Internet he helped build is far from finished, and changes are in store to meet growing demands for multimedia. Network providers now make only "best efforts" at delivering data packets, and Crocker said better guarantees are needed to prevent the skips and stutters now common with video.Cerf, now at MCI Inc., said he wished he could have designed the Internet with security built-in. Microsoft Corp.Yahoo Inc. and America Online Inc., among others, are currently trying to retrofit the network so e-mail senders can be authenticated - a way to cut down on junk messages sent using spoofed addresses.Many features being developed today wouldn't have been possible at birth given the slower computing speeds and narrower Internet pipes, or bandwidth, Cerf said.2.Digital CertificatesDigital certificates are data files used to establish the identity of people and electronic assets on the Internet. They allow for secure, encrypted online communication and are often used to protect online transactions.Digital certificates are issued by a trusted third party known as a certification authority (CA). The CA validates the identity of a certificate holder and “signs” the certificate to attest that it hasn’t been forged or altered in any way.New Uses For Digital CertificatesDigital certificates are now being used to provide security and validation for wireless connections, and hardware manufacturers are one of the latest groups to use them. Not long ago, Version Inc. announced its Cable Modem Authentication Services, which allow hardware manufacturers to embed digital certificates into cable modems to help prevent the pirating of broadband services through device cloning.Using Version software, hardware makers can generate cryptographic keys and corresponding digital certificates those manufacturers or cable service providers can use to automatically identify individual modems.This ‘ast-mile’authentication not only protects the value of existing content and services but also positions cable system operators to bring a broad new range of content, applications and value-added services to market.When a CA digitally signs a certificate, its owner can use it as an electronic passport to prove his identity. It can be presented to Web sites, networks or individuals that require secure access.Identifying information embedded in the certificate includes the holder’ s name and e-mail address, the name of the CA, a serial number and any activation or expiration data for the certificate. When the CA verifies a user’s identity, the certificate uses the holder’s public encryption key to protect this data.Certificates that a Web server uses to confirm the authenticity of a Web site for a user’s browser also employ public keys. When a user wants to send confidential information to a Web server, such as a credit-card number for an online transaction, the browser will access the public key in the server’s digital certificate to verify its identity.Role of Public-Key CryptographyThe public key is one half of a pair of keys used in public-key cryptography, which provides the foundation for digital certificates.Public-key cryptography uses matched public and private keys for encryption and decryption. These keys have a numerical value that’s used by an algorithm to scramble information and make it readable only to users with the corresponding decryption key.Others to encrypt information meant only for that person use a person’s public key. When he receives the information, he uses his corresponding private key, which is kept secret, to decrypt the data. A person's public key can be distributed without damaging the private key. A Web server using a digital certificate can use its private key to make sure that only it can decrypt confidential information sent to it over the Internet.The Web serve r’s certificate is validated by a self-signed CA certificate that identifies the issuing CA. CA certificates are preinstalled on most major Web browsers, including Microsoft Internet Explorer and Netscape Navigator.The CA certificate tells users whether they can trust the Web server certificate when it’s presented to the browser. If the validity of the Web server certificate is affirmed, the certificate’s public key is used to secure information for the server using Secure Sockets Layer (SSL) technology.Digital certificates are used by the SSL security protocol to create a secure “pipe” between two parties that seek confidential communication. SSL is used in most major Web browsers and commercial Web servers.3. Digital Wallets----A digital wallet is software that enables users to pay for goods on the Web ．It holds credit-card numbers and other personal information such as a shipping address ．Once entered，the data automatically populates order fields at merchant sites ．----When using a digital wallet，consumers don’t need to fill out order forms on each site when they purchase an item because the information has already been stored and is automatically updated and entered into the order fields across merchant sites ．Consumers also benefit when using digital wallets because their information is encrypted or protected by a private software code ．And merchants benefit by receiving protection against fraud ．----Digital wallets are available to consumers free of charge，and they’re fairly easy to obtain ．For example，when a consumer makes a purchase at a merchant site that’s set up to handle server-side digital wallets，he types his name and payment and shipping information into the merchant’s own form ．At the end of the purchase，one consumer is asked to sign up for a wallet of his choice by entering a user name and password for future purchases ．Users can also acquire wallets at a wallet vendor’s site ．----Although a wallet is free for consumers，vendors charge merchants for wallets ．----Digital wallets come in two main types: client-side and server- side ．Within those divisions are wallets that work only on specific merchant sites and those that are merchant agnostic ．----Client-based digital wallets，the older of the two types，are falling by the wayside，according to analysts，because they require users to download and install software ．A user downloads the wallet application and inputs payment and mailing information ．At that point，the information is secured and encrypted on the user’s hard drive ．The user retains control of his credit card and personal information locally ．----With a server-based wallet，a user fills out his personal information，and a cookie is automatically downloaded ．(A cookie is a text file that contains information about the user ．）In this scenario，the consumer information resides on the server of a financial institution or a digital wallet vendor rather than on the user’s PC ．----Server-side wallets provide assurance against merchant fraud because they use certificates to verify the identity of all parties ．When a party makes a transaction，it presents its certificate to the other parties involved ．A certificate is an attachment to an electronic message used to verify the identity of the party and to provide the receiver with the means to encode a reply ．----Furthermore，the cardholder’s sensitive data is typically housed at a financial institution，so there’s an extra sense of security because financial environments generally provide the highest degree of security ．----But even though wallets provide easy shopping online，adoption hasn’t been widespread ．----Standards are pivotal to the success of digital wallets ．----Last month，major vendors，including Microsoft Corp ．，Sun Microsystems Inc ．and America Online Inc ．announced their endorsement of a new standard called EMCL，or E-Commerce Modeling Language，to give Web merchants a standardized way to collect electronic data for shipping，billing and payment ．4. Grid StorageDefinition: Grid storage, analogous to grid computing, is a new model for deploying and managing storage distributed across multiple systems and networks, making efficient use of available storage capacity without requiring a large, centralized switching system.A grid is, in fact, a meshed network in which no single centralized switch or hub controls routing. Grids offer almost unlimited scalability in size and performance because they aren’t constrained by the need for ever-larger central switches. Grid networks thus reduce component costs and produce a reliable and resilient structure.Applying the grid concept to a computer network lets us harness available but unused resources by dynamically allocating and deal locating capacity, bandwidth and processing among numerous distributed computers. A computing grid can span locations, organizations, machine architectures and software boundaries, offering power, collaboration and information access to connected users. Universities and research facilities are using grids to build what amounts to supercomputer capability from PCs, Macintoshes and Linux boxes.After grid computing came into being, it was only a matter of time before a similar model would emerge for making use of distributed data storage. Most storage networks are built in star configurations, where all servers and storage devices are connected to a single central switch. In contrast, grid topology is built with a network of interconnected smaller switches that can scale as bandwidth increases and continue to deliver improved reliability and higher performance and connectivity.Based on current and proposed products, it appears that a grid storage system should include the following:Modular storage arrays: These systems are connected across a storage network using serial ATA disks. The systems can be block-oriented storage arrays or network-attached storage gateways and servers.Common virtualization layer: Storage must be organized as a single logical pool of resources available to users.Data redundancy and availability: Multiple copies of data should exist across nodes in the grid, creating redundant data access and availability in case of a component failure.Common management: A single level of management across all nodes should cover the areas of data security, mobility and migration, capacity on demand, and provisioning.Simplified platform/management architecture: Because common management is so important, the tasks involved in administration should be organized in modularfashion, allowing the auto discovery of new nodes in the grid and automating volume and file management.Three Basic BenefitsApplying grid topology to a storage network provides several benefits, including the following:Reliability. A well-designed grid network is extremely resilient. Rather than providing just two paths between any two nodes, the grid offers multiple paths between each storage node. This makes it easy to service and replace components in case of failure, with minimal impact on system availability or downtime.Performance. The same factors that lead to reliability also can improve performance. Not requiring a centralized switch with many ports eliminates a potential performance bottleneck, and applying load-balancing techniques to the multiple paths available offers consistent performance for the entire network.Scalability. It’s easy to expand a grid network using inexpensive switches with low port counts to accommodate additional servers for increased performance, bandwidth and capacity. In essence, grid storage is a way to scale out rather than up, using relatively inexpensive storage building blocks.四、译文新技术的计算机网络摘要：21世纪是信息经济的时代，作为这个时代的代表技术，计算机网络技术将在非常快的速度发展很快，不断创造性地将进入人们的工作，学习和生活中深。

网络工程专业外文翻译--GSM无线网络规划与网络优化

外文原文：GSM network planning and network optimizationBetween the fast growth mobile communication network capacity demand and the limited frequency resources contradiction seriously is puzzling the mobile communication operation business, the network planning and the network optimizes receives day by day takes. The network planning is in the mobile communication network construction important link, it all has the very important influence regarding the network construction cost and the movement quality. In overseas, the majority GSM network camp conveyance all extremely takes to the network constructions, invested the massive manpower, the physical resource and the financial resource in the network planning and the optimization. At present, the domestic various provinces mobile communication company and the association pass the company in its mobile communication equipment tender process also the equipment supplier's network planning and the optimized technology took an important inspection target object, from this is worthy of looking at the network planning and the optimization in the mobile communication network construction vital significance. First, network planning key contentFirst is to plans the region earlier period survey, including to the terrain, the landform, the building distribution, the transportation and the commercial development situation, inhabitant's living standard as well as their habits and customs and so on various aspects situation carries on the generalized analysis, thus forecast at present and future locality potential user group number. According to camp merchant grade of service, thus determined in entire region main part traffic load distribution and cloth station strategy, station disposition, stand number, investment scale and so on, fully considered the local high-rise building and the tower distribution, basically determines the stand distribution and the number. Regarding the stand position choice and the cover radius, must consider the telephone traffic demand quantity, the dissemination environment, about the good signal balance and so on to BTS the cover radius limit as well as the station construction comprehensive cost and so on many factors.The network planning goal will be constructs by the lowest cost conforms to the near future and the forward telephone traffic demand, has the certain grade of service the mobile communication network, thus will provide the formidable strut for the service development.The network planning is a more complex project, it receives the various factors the restriction, and therefore, it not merely is the simple technical question. Must especially point out in here is the radio wave propagation performance test, it is in the network planning process a not allow to neglect important aspect. It uses in the radio wave propagation model adjustment, thus forecasts the stand cover radius. To stand cover radius forecast is whether accurate, directly will affect the network construction quality and the cost, therefore, the overseas GSM operation businessman all very much will take to the network dissemination performance test.Second, the network optimizes fault analysis and countermeasureOnce after when the network completes, because the earlier period plan and actual userdevelopment existence certain deviation, creates the busy area resources tense and the idle area resources surplus situation, as well as the user like the voice which bumps into in the middle of the telephone conversation process off and on, the jam, wireless falls the speech and so on many phenomena, these all do not favor the service the development.In view of these situations, Engineer GSM must carry on the optimization to the network, while meets the general consumer need, causes the existing network to obtain the best economic efficiency, it is one item important moreover the long-term work.Because the network optimizes the plan is more complex than, on the one hand in this, our motion signal battalion salt merchants, specially is engaged in engineers who the network optimizes all to have the profound experience and the lesson, moreover network optimization and network planning close correlation, therefore many battalions of salt merchants in to had system dilatancy perhaps time the newly built system, but all without one exception optimizes and plans two parts when to carry on as the network construction important link the equipment tenders alone lists it, thus it can be seen the network optimization and the network planning are similarly important.1. fault analyses(1) pair plans the area cover, the frequency neighbouring frequency disturbs the plot to carry on the survey and the analysis, thus proposes to the plot antenna direction, the antenna angle of pitch, base-station system biggest emissive power (MAX_TX_BTS), biggest handset emissive power (MAX_TX_MS) as well as handset permission turning on time system network parameter and so on lowest turning on level (RXLEV_ACCESS_MIN) adjustment plans.(2) pair plans the area voice quality, the plot cut, the plot choice, the plot gravity separation, the jam, falls the speech and so on to carry on the survey and the analysis, discovers the question, proposes the solution.(3) basis plan area each base depot telephone traffic statistics, the cut and fall situations and so on speech to carry on the generalized analysis, carries on the adjustment to the plot radio frequency parameter and the network parameter, thus the appropriate readjustment each plot direction detection separates by gravity the boundary; Cuts the boundary to the plot to carry on the adjustment, causes the network various plots the telephone traffic load to be as far as possible balanced, and causes the network the cover and the disturbance situation can improve.The network optimizes the goal is analyzes the system the actual movement situation, discovers question which the existing network possibly exists, determined the solution, enhances the network performance stably, the guarantee network, the good movement.2. system optimization data origin(1)OMC telephone traffic statistical analysisIn the network various nets Yuan network performance statistical data, may carry on gathering through the OMC_R terminal.The OMC telephone traffic statistics are understood the network performance index the important way, it has the comprehensive network performance data, through the telephone traffic statistics, may understand each plot the traffic load, the channel availability factor, the TCH voice dropout rate, the TCH jam rate, the cut success ratio, the call completing rate and so on each target, thus understood various plots TCH, SDCCH, RACH and so on the channel takes with thesignaling load bearing situation, grasps the entire net the telephone traffic and the signaling current capacity, carries on the analysis to the existence question and the latent question, provides the important basis for the network optimization.The OMC telephone traffic statistics result all has the primary data result, the statistical analysis result, the graph form generally and so on several display modes, the optimized work should act according to the target generally which must inspect item of and the analysis demand, chooses the appropriate data display way, carries on the statistics and the analysis to each target.(2)CQT, DT testWith tests the handset to carry on the test to various plots cover field intensity, and makes the CQT test regularly; When to the plot jam, the cut, falls the speech, the voice quality and so on carries on the test, then has a part of outstanding test backstage analysis software to be able to provide to the test data demonstration, labelling, the statistical analysis and so on.Mainly is completes this advancement in the MOTOROLA system using the TEMS software, also is the data acquisition process.Lu Ce (DRIVE TEST) the goal lies in the appraisal network whole grade of service, understood various plots field intensity distribution, connection quality whether satisfies requests.When test, the road measured the equipment report user in the position, the base depot distance, the receive signal strength, the received signal quality rxqual, the switching point, the neighboring plot basic condition, the entire frequency band scan result and so on, and may record each test data completely, is advantageous for carries on the backstage analysis.The test data may according to the map statistical distribution, reflect effectively the wireless plot the cover scope, RXLEV, RXQUAL and the interference region, are advantageous for the analysis noise source position, the definite frequency allocation is whether reasonable, inspects the neighbouring area relations and the observation cut, falls the speech event the occurrence.In addition, but also whether can inspect the day to feed the system actual installment and the performance meets the anticipated design requirements.According to the test result, to the system parameter, the antenna condition carries on the corresponding adjustment, in which system parameter adjustment mainly includes: The adjustment base depot emissive power, the change frequency disposition plan, the cut level adjustment, the neighboring plot parameter establishment adjustment, the telephone traffic load adjustment as well as SDCCH and the TCH disposition number and the adjustment and so on, adjust the antenna condition to improve the cover, to reduce the disturbance to have the vital role.(3) pair of user's suit careful analysisAs a result of handset user distribution randomness, has possibly spread the network each quoin unit.Whether does the handset shout normally into and exhales, they often are the network quality quality first the feeling.Such as upward link random access channel rach RACH number disposition, downlink paging channel PCH and access grant channel AGCH number disposition, independent dedicated control channel SDCCH number disposition, plot telephone traffic whether has the jam, whether has the blind spot, whether between the plot has area cover and so on, we all may gain the first material from user's suit.中文译文：GSM无线网络规划与网络优化快速增长的移动通信网络容量需求与有限的频率资源之间的矛盾正严重困扰着移动通信运营商，网络规划和网络优化日益受到重视。

网络工程专业外文翻译--博客系统

外文原文：Blog systemWhat is a blog？Chinese "blog", derived from English words Blog / Blogger. Blog, short for a Weblog. Weblog, and the Web Log is actually a combination of words. Web, referring to World Wide Web, of course, refers to the Internet; Log of the original meaning is "logs", after referring to any type of flow records. Together to understand, Weblog on the network is a form of water or record referred to as "Web log." Blogger or Weblogger, is accustomed to daily records and use the tools of Weblog. Although earlier in the mainland or Taiwan, the translation of this concept of different (some known as "blog", some call it "recorded net", etc.), but has basically into "blog" Of the word. The term was first in the August 8, 2002 by the famous critic of the network Fang Xingdong and Wang Junxiu jointly put forward by the author. Blog, or blog all right, it is only a name, its original meaning or scope of the Weblog can not escape. But usually what we call the "blog" is the term can be used as Blogger or weblogger - refer to a blog of a class of people can also be used for the verb (the equivalent of the English Weblog or blog), referring to blog To reflect the behavior of a blog, is a third party can use the visual sense, that is, their blog written by the Blog. Therefore, "he / she is a blog, his / her blog every day" and "blog off what Bo»"in Chinese grammar and logic is correct. Only the use of different occasions only. What is a Blog » Said a long time, in fact, a Blog is a Web page, it is usually short and frequently updated by the Post (Post) posed by these posts in accordance with the year and date reverse order. Blog content and purpose are quite different, Blog of the content and purpose are quite different from other sites on the hyperlinks and comments on companies, individuals,the idea of the press to diaries, photos, poetry, prose, and even science fiction The publication or are posted. Blogs recorded many of the personal blog see, hear, think, there are some Blogs are a group of people based on a specific topic or area of common interests of the collective creativity. Weblog, or Blog to write these people is called Blogger or Blog writer. The blog, generally fall into three categories: First, hosted blog, do not have their own domain name registration, rental of space and the preparation of the page, as long as the blog are free to apply for registration to have their own blog space, is the most " Duokuaihaoxing "approach. Second, the blog site itself independent, have their own domain name, space and style pages, needs certain conditions. Fang Xingdong such as the establishment of the third is the subsidiary blog, their blog as a part of a Web site (such as a tab, a channel or an address). This could be between three categories of evolution, or even have both, one with a variety of blog sites.The distinction between hackers and blogThe term blog Mr. Fang Xingdong, founder of the blog and the distinction between hackers have such a section on: ① blog and, like hackers, but also "knowledge workers" of a type (Note: here said the hackers is that Like Linux, as members of the community rather than the production of destructive hackers). Hackers not so much from the strength of his own as a "self-employed knowledge" of intelligence, rather than from an organizational mechanism. This organizational mechanism - open, self-organization, self-optimization, it is precisely by the full knowledge sharing - the open source code - to guarantee. In this sense, the hacker is not so much that, rather than refer to a brand-new production methods and knowledge exchange methods. And the hackers do not like is that the first blog from the beginning is that a network communication modes - Following Email, BBS, IM (instant messaging) after the fourthexchange network, a form of media - from the media (We media, or "personal media"). In other words, only literally speaking, the first blog is a group of people, followed by the means of a personal, first of all is that "we", followed by the mean "I" - through a multi-link, "Overture - Introduction" - Web log, "I" become "us" and let more people into the "we" in the past "me." Knowledge Community "is their common blood. Blog and hackers in the world, borrowing Dunn's poem," Nobody is an island, "everyone is a vast land with a part of the blog is not a singleSelf-contained, but a knowledge network of nodes. Relatively speaking, the blog more obvious than the hackers demonstrated "nodes" to the nature.② compared with the hackers, the blog is much lower threshold of knowledge. Anyone can In a few minutes, such rapid growth was a blog - as long as he can have this interest. Blog the text provided a lot of information, but I often could not blog author (copyright holders), he has done , May provide the only link some of it. In addition, blog readers can also add their own links. Therefore, the traditional media and not the same, blog is often not the reader's attention toward their own, but has been adopted or Potential (may be with other people) links, one to focus attention toward "the Other." Most important thing is that blog readers to lead readers through their own so that the reader gradually become the author. From the knowledge and information Consumers become providers.The history of the development blogBlog history of the development of a long and tortuous, from the Internet at the beginning of a blog that is in some form. In fact, a website and blog early in the form of very similar - Administrator Tim • Lee Bonaventure (Tim Berners-Lee, inventor of the Internet) regularly update the site and a series of other sites (at that time only the number of 10). Later, the blog evolved into a share personal experiences and otherpersonal information that is useful manner. From the beginning of development, with a double feature on the blog, on the one hand it is great to write logs of online tools, on the other hand is also an excellent communication tool. Then the 1993-1996 year, NCSA and Netscape's "What's New" section, also has a blog site prototype. Blog from the real history in the late 1990s. Jesse James Garrett in 1998 published in the network Camworld travel diary blog community is lit the fuse for the fire, from this blog become a new trend. August 1999, Para ( is now, the predecessor of) the Internet for free, the Blogger software. Previously, the blog be called on only a few people probably still playing it. The results this way, as Ganchai run into the fire, many people use this software as a weapon, entered the blog team. Blog ranks began to open and multiply rapidly. By 2000, tens of thousands of blog started emerging, and become a hot concept. September 11, 2001: the World Trade Center terrorist attacks encountered, the blog has become an important information and disaster first-hand experience of an important source. Since then, the blog officially entered the mainstream of society perspective. It is precisely the terrorist attacks, so that the lives of vulnerable people, people to communicate important and most immediately the most effective way of transmitting information, a new awareness. 2004 is crucial for the development of the blog, thinking pioneer enterprises, such as management master •Tom Peters (Tom Peters), entrepreneurs built Kawasaki (Guy Kawaski), and others are beginning to experience the power of blog, in fact, now Economic class readers must work to set up blog to be complete, "wealth", "Business 2.0", and other global business magazine blog have also felt the effects of the world's enterprises have started to pay attention to this area. By the year 2005 around the world have 50 million more people to join the ranks of blog writing. By 2007, the number of global blog breakthrough 100 million. Although more than 1.3 billion compared to the netizens, is trivial. However, these blog's influence, has already exceeded his as anindividual, even as its original scope of the industry. Begun to attract the mainstream media's strong concern and obvious rise of the blog to feel the impact of traditional media. In addition to the United States, Britain, Hungary, Germany and other European countries also formed the blog momentum. Asia, including China's blog also started to feel the pulse. In 2002, the blog was to introduce the concept of China's rapid development and, in 2005, blog by the scale of growth in 2006, Chinese netizens registered blog space is more than 33 million. As of the end of November 2007, the Chinese blog space has reached 72.82 million, the number of blog author of 47 million, an average of nearly every four Internet users out of a blog author. Along with the increase in the number of registered, the blog to fast speed into the social life, gradually popular as Internet-based infrastructure services. And then bring about a series of new applications, such as the blog ads, blog search, corporate blog, mobile blog, blog publishing, an independent domain name blog, and other innovative business model, in the next few years, as a new The media phenomenon, the blog's influence may go beyond traditional media.Blog for the futureBecause the blog is published by the individual finishing Therefore, its individual elements, the style is the one to the relative. This feature can be used for classification and then in the blog articles and a link between the blog. (Node-use classification, are not necessarily have been classified, you can use as programming, inheritance and polymorphism, the article may belong to any major node, from this node, has its own unique classification. Here can be used more Method to the blog article classified as accurate. Such as: the more accurate the more detailed classification to the seizure by the time the easier it is to have found, and those on the classification of the more ambiguous it in more places to be found by, but its ranking Quegeng backward) use thisblog link between the formation of a wealth of information on the group, but is accurate and orderly, which will network all the blog articles accurate classification, will be a lot of Lingluan to focus on the blog 一起. When the blog long enough to organize managers can aggregate boost to a specific page. This blog based on the information exchange platform is created. But this time to allow the blog has more energy to the blog can also modular. These modules are additional. At this time when a sufficient number of novels published information platform generated when people can subscribe to this novel module. At this time the module can be integrated on the release of novels, subscription collection. Of course, not all and must be free of charge. For example, in a novel module is part of subscription fees, which justified the charges will be part of the novel to the publisher. This interest will be driven by more people writing novels and take advantage of this module release. Tigong and modules are not necessarily the blog managers, but according to some kind of agreement (such as: http) caused. Tigong module can also integrated in the module on the text of ads, fees can also use the module. Even QQ / msn This is also the ICQ instant messaging software can be integrated into the blog.At this time when the Internet blog in a network favorites module, the music and listen to music module, the film module, chat modules, the modules, novels module. . . . . At this time the blog has beenall-encompassing, but the blog style, style, the modules are tailor their users, is their own favorite.Blog periphery - to pick networkExtraction, also known as Web bookmarks, the English name is Social Bookmark, literal translation is "social bookmarks." The world's first network to pick the site founder Joshua invented the net to pick. Tongsudeshuo, the network is picking on the network on a massivefavorites. It provides is a collection, classification, sort and share the way the Internet information resources. Web site and use it to store information about the list, the use of labels (Tag) index so that the URL address classification and indexing resources in an orderly manner so that the web site and related social sharing of information possible. The majority interest in part of the WIKI from Wikipedia (Wikipedia) The success of Wikipedia is a free online encyclopedia, which relies on many contributors to increase and amend its entry. Since its inception in 2001, the English version of Wikipedia continued to expand, now contains 480,000 entries, and already have many other languages. Wikipedia is perhaps the most famous wiki, but it is not the first one. The world's first wiki is a knowledge base model is called the Portland (Portland Pattern Repository) computer programming site, •by Ward Cunningham (Ward Cunningham) was founded in 1995. What's the difference between wiki and blog » wiki has "edit this page" link, allowing visitors to revise the pages. The existence of this link is different from the wiki and blog's Web log, the latter two to allow readers to comment on specific feedback information, but in addition to edit the content on their own, can not modify any other things. blog can be used to establish a common interest-loving people of the community. The wiki on this basis more step forward a step, you can build consensus (consensus-building). Imagine: a group of people sitting in front of a whiteboard, anyone can add in the above ideas, to amend, or even obliterating little things, you can have a wiki on the general impression. Where are the advantages of wiki » To today's fast-paced commercial work as an example, the distance between good communication and the exchange of ideas to share(idea-sharing) will be the corporate competitive edge. Wiki visit to the requirements of only Internet connection and a Web browser, than some other collaborative applications and components easy to deploy and use. To let people share information on the wiki page can also reduce the load inbox, the staff reduction synergies between the number of e-mail sent.Why enterprises to wiki? Since the success of Wikipedia, the wiki on the discussion more and more, and this media with the collective potential is far from being developed. There is no doubt, wiki can be used for the internal and external applications. For some in-house network to update information in the presence of the company, wiki makes employees and customers to update their own to do. wiki can help adjust the internal development projects in this field has begun to do a wiki. wiki also can be used to build online customer communities, to provide advice and support. Some companies in the company open to the public on the site may also feel some fear, but with customer loyalty and satisfaction with the continuous upgrading, in return for their trust in the company will also continue to expand. Who controls the content of the wiki »Theoretically speaking, no one can control, and everyone can control. Every reader of the content on wiki have modify, add, delete and the right, as long as he feels fit. For some organizations, accept such a lack of centralized control of the state need to have more on the concept of a big change. looks like a wiki into the world without the invitation of the Government - of online vandalism of the people, they can arbitrarily change and even delete some important elements - but in reality, this almost does not happen. Instant case, the use of the wiki some of the basic set of rules is necessary. In order to prevent important information has been changed or deleted, the system administrator can be certain pages of "protection" so that it can not be modified. In fact, even if an important page has been deleted or modified, do not have to worry about. wiki is an online information database for each of its amendments will be recorded and is recoverable. How to get started wiki tour » A number of open source software can be downloaded for free, including TWiki. Other mainframe applications, such as Socialtext and JotSpot (in the testing phase) can also be downloaded to the Internet.Corporate blogBo Enterprise Network blog will be the latest technology and businessmen and the actual demand for the integration of businessmen and enterprises based on the practical application, launched a business blog of personalized service. It made up for the traditional model ofe-commerce in the business applications of the defects, at the same time integrate into the Western mode of application of the blog success stories and experiences, will be launched marketing (Marketing) as the core content of the blog services to enterprises and business enterprises . Corporate blog is different from the general blog, but also broke through the conventional e-commerce services, providing enterprises and businessmen in line with the actual needs of business applications, it is not simply in the original e-commerce sites in the Forum to increase a "blog "Function or become a" businessman's Collected Works ", but ground-breaking" blog "and the concept of organic combination ofe-commerce for enterprises to build a true sense of the Internet portal business and office, which covers the enterprises of all online business activities , Is not just limited to "Published articles and logs," but the coverage and business activities related to various aspects, is a veritable "one-stop" business commerce portal.Blog subscription serviceIn contrast to the traditional understanding of the subscribers, because the development of network technology, the more in-depth subscribe to subscribe to blog daily life, most of the news sites and blog sites offer RSS subscription feature more. RSS is a content-sharing easy way (also known as polymerization, Really Simple Syndication). Usually in the timeliness of the content and strong on the use of RSS subscriptions to more rapid access to information and sites that offerRSS output, to allow users access to the latest update site content. Internet users can help support the client in the polymerization RSS tools, content pages do not open the case to support reading RSS output site content. You generally need to download and install an RSS reader to manage the news, online is now more popular, do not have to install additional software, in any place on the Internet access you want to know the content without the need to do any of the data migration , Subscription, you will receive timely subscribe to the latest content.中文译文：博客系统什么是博客？中文“博客”一词，源于英文单词Blog/Blogger。

计算机网络简称英语词汇

ATU-C ADSL transmission Unit-Central 处于中心位置的ADSL Modem
ATI-R ADSL transmission Unit-Remote 用户ADSL Modem
CEPT 欧洲邮电委员会
CCK Complementary code keying
CLNP Connectionless network protocol 无连接的网络协议
CIDR Classless inter-domain routing 无类别的域间路由
ASE Application service element 应用服务元素
ASK 幅度键控
ACK 应答信号
ARQ Automatic repeat request 自动重发请求
ASN.1 Abstract syntax notation one 抽象语法符号1
ADSL Asymmetric digital subscriber line 非对称数字用户线路
ADSI Active directory scripting interface
CAU Controlled access unit 中央访问单元
CDDI Copper distributed data interface
CDPD Celluar digital packet data 单元数字分组数据
ATM Asynchronous transfer mode 异步传输模式
ABM Asynchronous balanced ronous response mode 异步响应方式
CS Convergence sublayer 汇集子层
CDMA Code division multiple access 码分多址

网络工程专业外文翻译--PLC控制系统设计的要点

外文原文：Plc control system design elementsOriginally, the PLC was represented by the acronym PC. There was some confusion with using this acronym as it is commonly accepted to represent personal computer. Therefore, PLC is now commonly accepted to mean programmable logic contoller.A PLC is a user-friendly, microprocessor-based specialized computer that carries out control functions of many types and leves of complexity. Its purpose is to monitor crucial process parameters and adjust process operations accordingly. It can be programmed, controlled, and operated by a person unskilled in operating computer. Essentially, a PLC’s operator draws the lines and devices of ladder diagrams with a keyboard onto a display screen. The resulting drawing is converted into computer machine language and run as a user program.The computer takes the place of much of the external wiring required for control of a process. The PLC will operate any system that has output devices that go on and off (known as discrete, or digital, outputs). It can also operate any system with variable (analog) outputs. The PLC can be operated on the input side by on-off devices (discrete, or digital) or by variable (analog) input devices.Today, the big unit growth in the PLC industy is at the low end-where small keeps getting smaller. When a few years ago the micro PLC entered the market, some thougt that these devices had “bottomed out”. Now,nano PLCs-generally defined as those with 16 or fewer I/O-are spreading. Some can fit into your shirt pocket, being no larger than a deck of cards and at the time of this writing, PLC Direct plants to introduce a PLC the size of a box of Tic-Tac candy that will include many features of current micro models.The first PLC systems evolved from conventional computers in the late 1960s and early 1970s. These first PLCs were installed primarily in automotive plants. Traditionally, The auto plants had to be shut down for up to a month at model changeover time. The early PLCs were used along with other new automation techniques to shorten the changeover time. One of the major time-consuming changeover procedures had been the wiring of new or revised relay and control panels. The PLC keyboard reprogramming procedure replaced the rewiring of a panel full of wires, relays, timers and other components. The new PLCs helped reduce changeover time to a matter of few days.There was a major problem with these early 1970s computer/PLC reprogramming procedures. Theprograms were complicated and required a highly trained programmer to make the changes. Through the late 1970s, improvements were made in PLC programs to make them somewhat more user friendly; in 1978, the introduction of the microprocessor chip increased computer power for all kinds of automotion systems and lowered the computing cost. Robotics, automotion devices, and computers of all types, including the PLC, consequently underwent many improvements. PLC programs, written in high-level language, became more understandable to more people, and PLCs became more affordable.In the 1980s, with more computer power per dollar available, the PLC came into exponentially increasing use. Some large electronics and computer companies and some diverse corporate electronics divisions found that the PLC had become their greatest volume product. The market for PLCs grew from a volume of $80 million in 1978 to $1 billion per year by 1990 and is still growing. Even the machine tool industry, where compute numerical controls (CNCs) have been used in the past, is using PLCs. PLCs are also used extensively in building energy and security control systems. Other nontraditional uses of PLCs, such as in the home and in medical equipment, haved exploded in the 1990s and will increase as we enter the new millennium.A person knowledgeable in relay logic systems can master the major PLC functions in a few hours, These functions might include coils, contacts, timers and counters. The same is true for a person with a digital logic background. For persons unfamiliar with ladder diagrams or digital principles, howere, the learning process takes more time.A person knowledgeable in relay logic can master advanced PLC functions in a few days with proper instruction. Company schools and operating manuals are very helpful in mastering these advanced functions. Advanced functions in order of learning might include sequence/drum controller, register bit use, and more functions.Following are 8 major advantages of using a programmable controller.①Flexibility. In the past, each different electronically controlled production machine required own controller; 15 machines might require 15 different controllers. Now it is possible to use just one model of a PLC to run any one of the 15 machines.②Implementing Change and Correcting Errors. With a wired relay-type panel, any program alterations require time for rewriting of panels and devices. When a PLC program circuit or sequence design change is made, the PLC program can be changed from a keyboard sequence in a metter of minutes.No rewiring is required for a PLC-controlled system.③Large quantities of contacts. The PLC has a large number of contacts for each coil available in its programming.suppose that a panel-wired relay has four contacts and all are in use when a design change requiring three more contacts is made. Time would have to be taken to procure and install a new relay or relay contact block. Using a PLC, howere, only three more contacts would be typed in. the three contact would be automatically available in the PLC. Indeed, a hundred contacts can be used from one relay-if sufficient computer memory is available.④Lower cost. Increased technology makes it possible to condense more functions into smaller and less expensive packages. Now you can purchase a PLC with numerous relays, timers and counters, a sequencer, and other function for a few hundred dollars.⑤Pilot Running. A PLC programmed circuit can be evaluated in the office or lab. The program can be typed in, tested, observed, and modified if needed, saving valuable factory time. In contrast, conventional relay systems have been tested on the factory floor, which can be very time consuming.⑥Visual Observation. A PLC circuit’s operation can be seen during operation directly on a CRT screen. The operation or misoperation of a circuit can be observed as it happens. Logic paths light up on the screen as they are energized. Troubleshooting can be done more quickly during visual observation. In advanced PLC systems, an operator message can be programmed for each possible malfunction.In advanced PLC systems, an operator message can be programmed for each possible malfunction. The malfunction description appears on the screen when the malfunction is detected by the PLC logic. Advanced PLC systems also may have descriptions of the function of each circuit component.⑦Speed of Operation. Relays can take an unacceptable amount of time to actuate. The operational speed for the PLC program is very fast. The speed for the PLC logic operation is determined by scan time, which is a matter of milliseconds.⑧Ladder or Boolean Programming Method. The PLC programming can be accomplished in the ladder mode by an electrician or technician. Alternatively, a PLC programmer who works in digital or Boolean control systems can also easily perform PLC programming.In modern industrial production equipment, and large numbers of simulations of the control devices, such as the cease electrical, electromagnetic devices to turn, the number of products, temperature, Ap power, and set the flow control, the automatic control of the industrial site, If a programmable controller(PLC) to resolve the issue has become a cybernetic one of the most effective tools, this article describes Plc control system design should be noted. Hardware purchase many products currently on the market Plc, with the exception of domestic brands, foreign : Japan Omron, Mitsubishi, FUJJ, ANASONIC, Germany Siemens, Korean LG. In recent years, Plc greater decline in the prices of products, increasing its performance cost rate.This is a technical staff chosen Plc important reasons. Then, how to purchase Plc products?First, the system should first determine the size of single control system with Plc or using Plc networking, thus calculating Plc importing, exporting. Few, and in some Plc to be in real need have a certain cushionSecond, determine the type of load under Plc export-led type of load is the DC or exchange-type, big or small currents, and Plc export points such as the frequency of movements, the use of relays to determine export-export, or transistor output, or goods of export gates. Different load choose different ways to export to the operating system's stability is very important.Third, the storage capacity and speed while foreign manufacturers of Plc products essentially the same, but there are some differences. Currently the company has not yet found full compatibility between products. The development of software companies are not the same, and users of storage capacity and procedures to implement the Directive speed are two important indicators. General greater storage capacity, faster speed on the Plc higher prices, but should be based on system size reasonable choice Plc products.Fourth, programming devices Plc programming can purchase three ways : Using hand-held programming device programming in general, it can provide businesses phrases programming language table. This approach inefficient, but the capacity of small systems, the products more suitable for small consumption, and small size, ease of debugging scene, but also lower costs. Using graphical programming device programming, the programming device used Trapezoid Chart programming for visual and general electrical personnel shortly be applied easily, but the programming device prices higher. Using IBM personal computers and software packages using Plc programming, this approach is the most efficient way, but most of the company's Plc development software packages expensive, and that means not at the scene debugging. Therefore, the system should be based on the size and level of difficulty, the length of the development cycle and reasonable funding of the purchase Plc products.Fifth, And large companies to choose their quality guaranteed products, and good technical support,after sales services are generally better, but also help expand your product and software upgrades.For small systems, such as 80 points within the system. Generally do not need expansion; When a larger system, we must expand. Different companies products to the total points system and the expansion of the number of modules have limitations when expansion can not meet the requirements, can network structure; At the same time, some manufacturers of individual products do not support the expansion module directives, in software development, we must pay attention to. When using such simulation module temperature, some of the manufacturers, see related technical manuals. Many types of companies expansion modules, such as single-input modules, single output modules, input output modules, temperature modules, high-speed input module. This modular design Plc product development provided for the convenience of users.When using a Plc network design, its much more difficult to control than single Plc. First you should choose their own more familiar type, its basic instructions and a more in-depth understanding of the functional commands, and the speed and direction of the implementation of storage capacity users should also be careful about the procedure. Otherwise, you can not adapt to the real-time requirements, resulting in the collapse of the system. In addition to communications interfaces, communication protocols, data transmission speed should also be considered. Finally, we must seek to Plc businessmen network design and software technical support and detailed technical information for the selection of several workstations in your system size.In the preparation of the software, should first become familiar with the use of Plc software products specification, the question skilled later programming. If using graphical programming device or software package programming may direct programming, if using hand-held programming device programming, should be painted Trapezoid Chart before programming, so can less mistakes speed was fast. After the first air conditioning programming procedures to be normal functioning of all, again in equipment debugging.中文译文：PLC控制系统设计的要点可编程序控制器 (可设计的控制器) 本来应简称个人计算机，为了与个人计算机的简称个人计算机相区别,一般将它简称为 PLC(可设计的逻辑控制器)。

计算机与网络英汉对照词典（二）_计算机英语词汇

[f]file server 文件服务器fcc & bcc 转发与密送flash 动画制作软件failback 自动恢复fat 文件分配表ftp server 文件传输服务器fax modem 传真调制解调器fddi 光纤分布式数据接口fat 文件分配表flash 动感网页制作工具ftp 文件传输协议fat32 32位文件分配表firewall 防火墙flash flashfull－duplex transmissions 全双工传输front－end system 前端（台）系统front－end processor 前端（台）处理机frequency division multiplexing 频分多路复用frames in communication 通信帧frame relay 帧中继fractional t1/fractional t3 部分t1/部分t3forwarding 转发flow control methods 流控方法finger finger实用程序filtering 筛选，过滤file transfer protocol 文件传输协议file transfer access and management 文件传输访问和管理file systems in the network environment 网络环境中的文件系统file systems，distributed 分布式文件系统filesharing 文件共享file server 文件服务器fileand directory permissions，windows nt windows nt的文件和目录许file and directory attributes，netware netware的文件和目录属性fiber channel 光纤通道fiber－optic cable 光缆fiber distributed data interface 光纤分布式数据接口federated naming services，sunsoft onc sunsoft onc的联合命名服务federated database 联合数据库federal information processing standards 联邦信息处理标准fax servers 传真服务器 [g]gprs 通用分组无线业务gprs 通用分组无线业务3g 第三代移动通信gui 图形用户界面gateway 网关groupware 群件groups 组grounding problems 接地问题government osi profile 政府osi框架文件glue，oracle oracle的glue解决方法global naming services 全局命名服务gateway－to－gateway protocol 网关对网关协议gateway 网关，信关[h]hdf 层次型数据格式hardware 硬件http 超文本传输协议hacker 黑客html 超文本标记语言hub 集线器http 超文本传输协议html 超文本链接标示语言hard disk 硬盘hubs hub，集线器，集中器hub management interface hub管理接口hot fix，novell netware novell netware的热修复host 主机horizontal wiring system 水平布线系统hop 跳跃（计）数，过路数，中继数homogeneous network environments 同构网络环境home directory 私人目录high－speed serial interface 高速串行接口high－speed networking 高速联网高速网包括传输速度高于在1990年前占主导地位的传统传输速度的lan和whigh performance routing（hpr），ibm ibm 的高性能路由选择high performance parallel interface 高性能并行接口high performance file system 高性能文件系统high－level data link control 高级数据链路控制（规程）high capacity storage system（hcss），novell netware novell netware的大容量存储系统high－bit－rate digital subscriber line 高位速率数字用户专用线heterogeneous network environments 异构网络环境hermes，microsoft microsoft的企业网管理系统handshaking 握手，联络，信号交换half－duplex transmission 半双工传输[i]imap4 信息访问协议4insert mode 插入模式ipaq pocket pciis internet信息服务器ib 智能大厦irda 红外线传输装置iis 网络信息服务器ia 信息家电inf file 适配器安装信息文件instructions cache 指令缓存inf file 信息文件internet backbone internet骨干网interface 界面icon 图标icon 图标icon 图标icon 图标icon 图标it 信息技术产业internal bus 内部总线iis internet信息服务器it 信息技术ide 集成驱动电子设备ip 网络协议irc 互联网中转聊天icp 互联网内容提供商icp 互联网内容提供商isohronous service 等时服务is－is interdomain routing protocol is－is域间路由选择协议isdn/b－isdn 综合业务数字网/宽带综合业务数字网iridium system 铱系统interrupts 中断interprocess communication 进程间通信interoperability 互操作性，互用性internetwork routing 网间路由选择internetwork packet exchange 网间分组交换internetworking 网络互联internet protocol internet网络协议，因特网协议internet engineering task force internet工程任务组internet internet网因特网[j]jpeg 联合图像专家组规范jsp 网页控制技术java 编程语言jukebox optical storage device 自动换盘光盘存储设备jabber 超时传输，jabber传输。

网络工程师术语中英文对照

网络术语中英对照1。

ADSL （Asymmetric Digital Subscriber Line) 非对称数字环路2。

ANSI (American National Standard Institute) 美国国家标准协会3。

APIPA (Automatic Private IP Addressing) 自动私有IP寻址4. AppleTalk 由Apple公司推出的一种多层协议,一种可路由协议组5。

ARP （Address Resolution Protocol）地址解析协议6。

ARQ （Automatic Repeat Request) 自动重发请求7。

ASIC (Specific Integrated Circuit（Chip)）专用集成电路芯片8。

ASN。

1 (Abstract Syntax Notation One）一种用于描述结构化客体的结构和内容的语言. 抽象语法定义9. ATM （Asynchronous Transfer Mode) 异步传输模式10. BBS （Bulletin Board System）电子公告板11. BGP （Border Gateway Protocol）边界网关协议12. B-ISDN （Broadband Integrated Services Digital Network）宽带综合业务数字网13. BOOTP (BOOTstrapping Protocol) 引导协议14. BRI （Basic Rate Interface) ISDN基本速率15。

Bridge 网桥16。

BUS (Broadcast/Unknown Server) 广播和未知服务器17。

CA Communication Automatization 通信自动化18。

Cable Modem 电缆调制解调器19。

CATV 公用天线电视20。

CCITT 国际电话电报咨询委员会21。

网络工程师英语词汇

网络工程师英语词汇网络工程师英语词汇为题网络工程师是负责设计、开发和维护计算机网络系统的专业人士。

他们需要熟悉各种网络技术和协议，并且具备良好的英语能力，因为英语是网络领域的主要工作语言之一。

下面将介绍一些与网络工程师相关的英语词汇。

1. Network（网络）- 一组相互连接的计算机和设备，通过数据链路进行通信和共享资源。

2. Router（路由器）- 连接多个网络的设备，能够根据规则将数据包转发到目标网络。

3. Switch（交换机）- 用于在局域网内传输数据的设备，能够根据MAC地址将数据包转发到目标设备。

4. Firewall（防火墙）- 用于保护计算机网络免受未经授权的访问和网络攻击。

5. Protocol（协议）- 规定了计算机网络中设备之间通信的规则和标准，如TCP/IP协议。

6. IP Address（IP地址）- 用于标识计算机或设备在网络中的唯一地址，可以是IPv4或IPv6地址。

7. DNS（Domain Name System）- 用于将域名转换为对应的IP 地址的系统。

8. VPN（Virtual Private Network）- 用于在公共网络上建立私密连接的安全通信方法。

9. LAN（Local Area Network）- 局域网，用于连接在小范围内的计算机和设备。

10. WAN（Wide Area Network）- 广域网，用于连接较大范围内的计算机和设备。

11. Bandwidth（带宽）- 网络传输速度的衡量单位，表示单位时间内能够传输的数据量。

12. Latency（延迟）- 网络传输中的时延，表示数据从发送到接收所需要的时间。

13. VPN（Virtual Private Network）- 虚拟专用网络，用于在公共网络上建立私密连接的安全通信方法。

14. DHCP（Dynamic Host Configuration Protocol）- 动态主机配置协议，用于自动分配IP地址和其他网络配置。

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外文原文：COMPUTER NETWORKSDATE COMMUNICATIONSOne of the functions of the host computer is to store the applications programs for the various secondaries.The end equipment which either generates the digital information for transmission or uses the received digital data can be computer ,printers ,keyboards, CRTs, and so on. This equipment generally manipulates digital information internally in word units—all the bits that make up a word in a particular piece of equipment are transferred in parallel. Digital data, when transmitted, are in serial form. Parallel transmission of an 8-bit word require eight pairs of transmission lines—not at all cost-effective. Data terminal (DTE) is a general phrase encompassing all of the circuitry necessary to perform parallel-to-serial and serial-to-parallel conversions for transmission and reception respectively and for data link management. The UART (Universal Asynchronous Receiver/Transmitter) and USART (Universal Asynchronous/Asynchronous Receiver/Transmitter) are the devices that perform the parallel-to-serial and serial-to-parallel conversions. The primary DTE includes a line control unit (LCU or LinCo) which controls the flow of information in a multipoint data link system. A station controller (STACO) is the corresponding that belonged to the subscriber in a data link system. Between the DTEs, starting with the modems, was communications equipment owned and maintained by Telco property.Data communications equipment (DCE) accepts the serial data stream from the DTE and converts it to some form of analog signal suitable for transmission on voice-grade lined. At the receive end, the DCE performs the reverse function of converting 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 considered a form of analog-to-digital converter. The most common of modulation by modems are frequency shift keying (FSK), phase shift keying (PSK), and quadrature amplitude modulation (QAM). This is a typically data transmission mode using the analog telephone lines. If you transmit data bydigital channel (sometimes it is called “Digital T-carrier”), a pulse Code Modulation (PCM) equipment must be used. A microwave transmission system can also be used for the data communication. Finally, you can use the satellite communication system for data transmission.If the cables and signal levels used to interconnect the DTE and DCE were left unregulated, the variations generated would probably be proportional to the number of manufacturers. Electronics industries Association (EIA) , an organization of manufactures with establishing the DTE and modem. This is a 25-pincable whose pins have designated functions and specified signal levels. The RS-232C is anticipated to be replaced by an update standard.ARCHITECTURE OF COMPUTER NETWORKSComputer network is a complex consisting of two or more conned computing units, it is used for the purpose of data communication and resource resource sharing. Design of a network and its logical structure should comply with a set of design principles, including the organization of functions and the description of data formats and procedure. This is the network architecture and so called as a set of layers and protocols, because the architecture is a layer-based.In the next 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 model is shown in Fig.14-2(minus the physical medium). This model is based on a proposal developed by the International Standards Organizations (OSI) as the first step toward international standardization of the protocols used in the various layers. The model is called the ISO OSI (Open System Interconnection) Reference Model because it deals with connecting open systems--that is, systems that are open for communication with other systems, We will usually just call it the OSI model for short.The OSI model has seven has seven layers. Note that the OSI model itself is not a network architecture because it does not specify the exact services and protocols to be used in each layer. It just tells what each layer should do. However , However, ISO has also produced standards for all the layers, although these are not part of the reference model itself. Each one has been published as a separate international standard.2.The TCP/IP Reference ModelThe TCP/IP reference model is an early transport protocol which was designed by the US Department of Defence (DOD) around in 1978. It is often claimed that it gave rise the OSI “connectionless”mode of operation. TCP/IP is still used extensively and is called as a industrial standard of internet work in fact, TCP/IP has two parts: TCP and IP. TCP means it is on the transport layer and IP means it is on the network layer separately.(1)There are two end-to-end protocols in the transport layer, one of which is TCP(Transmission Control Protocol) , another is UDP (User Datagram Protocol).TCP is a connection-oriented protocol that allows a byte stream originating onone machine to be delivered without error on any other machine in the internet.UDP is an unreliable, connectionless protocol for application that do not wantTCP’s sequencing of flows control flow control and wish to provide their own.(2)The network layer defines an official packet format and protocol called IP(Internet protocol). The job of the network layer is to deliver IP packets wherethey are supposed to go.The TCP/IP Reference Model is shown in Fig.14.3. On top of the transport layer is the application layer, It contains all the higher-level protocols. The early ones included virtual terminal (TELNET), (FTP), electronic mail (SMTP) and domain name service(DNS).WIDE AREA NETWORKA wide area network, or WAN, spans a large geographical area, often a country or continent . It contains a collection of machines intended for running user (i. e. , application) programs. We will follow traditional usage and call these machines hosts. By a communication subnet, or just subnet for short. The job of the subnet is to carry messages from host to host, just as the telephone system carries words from speaker to listener. By separating the pure communication aspects of the network (the subnet) from the application aspects (the hosts), the complete network design is greatly simplified. Relation between hosts and the subnet is shown in Fig.14-4.One of many methods that can be used to categorize wide area networks is with respect to the flow of information on a transmission facility. If we use this method to categorize wide area networks, we can group them into three basic types: circuit switched, leased line and packet switched.1.CIRCUIT SWITCHED NETWORKSThe most popular type of network and the one almost all readers use on a daily basis is a circuit switched network. The public switched telephone network, however, is not limited to the telephone company, By purchasing appropriate switching equipment, any organization can construct their own internal circuit switched network and, if desired, provide one or more interfaces to the public switched network to allow voice and data transmission to flow between the public network and their private internal network2．LEASED LINE NETWORKSThis is a dedicated network connected by leased lines. Leased line is a communications line reserved for the exclusive use of a leasing customer without inter-exchange switching arrangements. Leased or private lines are dedicated to the user. This advantage is that the terminal or computer is a always physically connected to the line. Very short response times are met with service.3.PACKET SWITCHING NETWORKSA packet network is constructed through the use of equipment that assembles and disassembles packets, equipment that routes packet, and transmission facilities used to route packets from the originator to the destination device. Some types of data terminal equipment (DTE) can create their own packets, while other types of DTE require the conversion of their protocol into packets through the use of a packet assembler / disassemble (PAD). Packets are routed through the network by packet switches. Packet switches examine the destination of packets as they flow through the network and transfer the packets onto trunks interconnecting switches based upon the packet destination destination and network activity.Many older pubic networks follow a standard called X.25. It was developed during 1970s by CCITT to provide an interface between public packet-switched network and their customers.CCITT Recommendation X.25 controls the access from a packet mode DTE, such as aterminal device or computer system capable of forming packets, to the DCE at a packet mode. CCITT Recommendation X.28 controls the interface between non-packet mode devices that cannot interface between the PAD and the host computer. CCITT Recommendation X.3 specifies the parameter settings on the PAD and X.75 specifies the interface between packet network.LOCAL AREA NETWORKLocal area data network , normally referred to simply as local area network or LANs, are used to interconnect distributed communities of computer-based DTEs located within a building or localized group of building. 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. Alternatively, it may be complex. Since all the equipment is located within a single establishment, however, LANs are normally installed and maintained by the organization. Hence they are also referred to as private data networks.The main difference between a communication path established using a LAN and a connection made through a public data network is that a LAN normally offers much higher date transmission rates because of the relatively short physical separations involved. In the context of the ISO Reference Model for OSI, however, this difference manifests itself only at the lower network dependent layers. In many instances the higher protocol layers in the reference model are the same for both types of network.Before describing the structure and operation of the different types of LAN, it is perhaps helpful to first identify some of the selection issues that must be considered. It should be stressed that this is only a summary; there are also many possible links between the tips of the branches associated with the figure.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, which is a variation a variation of the bus and ring. Sometimes it is called hub/tree topology.2. Transmission mediaTwisted pair, coaxial cable and optical fiber are the three main type 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. They are carrier-sense-multiple-access with collision detection (CSMA/CD), for bus network topologies, and control token, for use with either bus or ring networks.CSMA/CD is used to control multiple-access networks. Each on the network “listens”before attempting to send a message, waiting for the “traffic” to clear. If two stations try to sent their messages at exactly the same time, a “collision” is detected, and both stations are required to “step back” and try later.Control token is another way of controlling access to a shared transmission medium that is by the use of a control (permission) token. This token is passed form one DTE to another according to a defined set of rules understood and adhered to by all DTEs connected to the medium. ADTE may only transmit a frame when it is in possession of the token and, after it has transmitted the frame, it passed the token on to allow another DTE to access the transmission medium.中文译文：计算机网络14.1 数据通信图14-1是数据通信链路的简化框图。