计算机网络中英文对照外文翻译文献
网络工程局域网中英文对照外文翻译文献
中英文对照外文翻译(文档含英文原文和中文翻译)PUTER NETWORKSDATE COMMUNICATIONSThe 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 by digital 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.2.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 usedextensively 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 on one machine to be delivered without error on any other machine in the internet. UDP is an unreliable, connectionless protocol for application that do not want TCP’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 where they 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), file transfer (FTP), electronic mail (SMTP) and domain name service(DNS).3.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 a terminal 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.4.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.1．计算机网络数据通信端设备可以是计算机、打印机、键盘、CRT等，它们可以产生要发送的数字信息，也可使用所接收的数字数据。
计算机网络体系结构论文外文翻译
附录AWith the new network technology and application of the continuous rapid development of the computer network should. Use of becoming increasingly widespread, the role played by the increasingly important computer networks and human. More inseparable from the lives of the community's reliance on them will keep growing.In order for computers to communicate, they must speak the same language or protocol. In the early days of networking, networks were disorganized in many ways. Companies developed proprietary network technologies that had great difficulties in exchanging information with other or existing technologies; so network interconnections were very hard to build. To solve this problem, the International Organization for Standardization（ISO）created a network model that helps vendors to create networks compatible with each other.Finding the best software is not easy. A better understanding of what you need and asking the right questions makes it easier. The software should be capable of handling challenges specific to your company. If you operate multiple distribution centers, it may be beneficial to create routes with product originating from more than one depot. Few software providers though, are capable of optimizing routes using multiple depots. The provider should be able to support installation of its product. Make sure to clearly understand what training and software maintenance is offered.Obviously, selecting the right routing/scheduling software is critically important. Unfortunately, some companies are using software that may not be best suited to their operation. Logistics actives with responsibility for approving the software ought to be comfortable they've made the right decision. It is important to realize that not all routing/scheduling software is alike！There questions to ask are： Which operating system is used？ How easy is the software to use？ Here is a good way to tell. Ask if its graphical user interface（GUI）is flexible. Find out about installation speed - how long does it take？ Is the software able to route third party customers with your core business？When was the software originally released and when was it last upgraded？In 1984, ISO released the Open Systems Interconnection（OSI）reference model, which is a well-defined set of specifications that ensures greater compatibility among various technologies. In fact, OSI is a description of network communication that everyone refers to. It is not the only network model, but it has become the primary model for network communication. You will see further in this chapter, that the TCP/IP model is only a reduced version of the OSI model. The OSI model consists of seven layers, each illustrating a particular network function.meanwhile, ASP continues to evolve. With the arrival of the millennium came the arrival of ASP version 3. 0. Version 3. 0 was released along with Internet Information Server（IIS）version 5. 0 as part of the highly anticipated Microsoft Windows 2000. By far, the most important new feature of version 3.0 is the addition of a seventh, intrinsic object called ASP Error which should greatly simplify error handling. Other new features include the addition of three new methods to the Server object, and two new methods to both the Application object and the Session object.When programmers design an image editor for example, they don't have to think about adding OSI Layer 7 capabilities to that software, because it has no need for communication with other computers. On the other hand, when creating an FTP client, they must add communication capabilities to that software. At Layer 7 we usually find Telnet, FTP, HTTP, SMTP, SNMP, or SSH. When we say, For Example, Layer 7 filtering, we refer to filtering application data, regardless of what port or computer it may come from.OSI will be a computer network architecture（architecture）is divided into the following seven：The first layer：physical layer（Physical Layer）, provides communications equipment for the mechanical, electrical and functional characteristics and process for the establishment, maintenance and removal of the physical link connection. Specifically, the provisions of the mechanical properties required for network connectivity connector dimensions, pin number and order situation, etc. ;the provisions of the electrical characteristics of the physical connection in the bit stream transmission line signal level of the size, impedance matching , transfer rate from the constraints; features refers to the distribution of the various signals to the exact meaning of the signal, that is the definition of the DTE and DCE function between the various lines; order characteristics of the definition of the use of bit stream signal transmission lines for a group of rules refers to the physical connection of the establishment, maintenance, exchange of information, DTE and DCE on the circuit on double-action series. In this layer, data units known as bits （bit）. Belong to the typical definition of the physical layer specification included： EIA / TIA RS-232, EIA / TIA RS-449, V. 35, RJ-45 and so on.The second layer： data link layer（Data Link Layer）： in the physical layer bit stream to provide services based on adjacent node between the data link, through the provision of error control data frame（Frame）in the channel error-free transmission, and the action of the series circuit. Data link layer in the physical media is not reliable to provide reliable transmission. The role of this layer include： addressing the physical address, data framing, flow control, data error, such as re-issued. In this layer, data units known as the frame（frame）. Data link layer protocol, including representatives of： SDLC, HDLC, PPP, STP, such as frame relay.The third layer is the network layerIn the computer network to communicate between two computers may be a lot of data link may also go through a lot of communication subnet. Network layer of the task is to choose a suitable inter-network routing and switching nodes, to ensure timely delivery of data. Network layer will provide the data link layer packet frame components, including network layer in the package header, which contains the logical address information - - the source site and destination site address of the network address. If you're talking about an IP address, then you are in dealing with the problem of Layer 3, which is “data packets”, rather than layer 2 of the “frame. ” IP is layer 3 part of the problem, in addition to a number of routing protocols and ARP（ARP）. All things related to routing in Layer 3 processing. Address resolution and routing is an important objective of Level 3. Network layer can also achieve congestion control features such as Internet interconnection. In this layer, data packets as the unit（packet）. Representatives of the network layer protocol, including: IP, IPX, RIP, OSPF, etc…The fourth tier is the transport layer process information. At fourth floor unit, also known as data packets（packets）. However, when you talk about TCP protocol, such as concrete and specific when the name, TCP data unit known as paragraph（segments）and the UDP protocol data unit referred to as “datagram （data grams）”. This layer is responsible for obtaining all the information, therefore, it must be tracking data cell debris, out-of-order packets arrive in the transfer process and other possible risk. No. 4 for the upper layer to provide end-to-end（the end-user to end-users）of a transparent and reliable data transmission services. Transparent by means of transmission is transmitted in the communication process of the upper layer shielding the communication transmission system details. Representatives of the Transport Protocol： TCP, UDP, SPX, etc…The fifth layer is the session layerThis layer can also be known as the dialogue meeting between layers or layer, in the session layer and above the high-level, the data transmission is no longer the other named units, known collectively as the message. Session layer does not participate in specific transmission, It provides, including access to authentication and session management, including the establishment and maintenance of mechanisms for communication between applications. If the server to verify user login is completed by the session layer.The sixth layer is Presentation LayerThe main solution to support this level of information that the problem of syntax. For the exchange of data will be suitable for a user from the abstract syntax, into a system suitable for the use of OSI transfer syntax. To provide formatting and conversion of that data services. Data compression and decompression, encryption and decryption so that the layers are responsible for.The seventh layer application layer, application layer for the operating system, applications or network services access the network interface. Agreement on behalf of the application layer, including: Telnet, FTP, HTTP, SNMP, etc. .Through the OSI layers, information from a computer software application for transfer to another application. For example, computer A on the application to send information to the computer application B, then A computer application in information need to be sent to the Application Layer（seventh layer）, and then this layer will be sent to that level of information（sixth floor）, indicating that the data layer will be transferred to the session layer（fifth layer）, and so continue until the physical layer（first layer）. In the physical layer, data is placed in the physical network media and sent to computer B. The physical layer of computer B to receive data from the physical media, and then send information up to data link layer（second layer）, data link layer and then to the network layer, until the information in order to arrive at the application layer of computer B. Finally, the application layer of computer B and then the application information to the receiving end, thus completing the communication process. The following describes the icons in the process.OSI's seven control the use of a wide range of information and other computer systems to communicate the corresponding layer. Control information contained in these special requests, and show that they correspond to the OSI layer exchange. Data at every level of the head and tail to bring the two basic forms of control information.For one to send down from the previous data, additional control information in the front as the head, attached to the back of the end of the control information is called. However, data from one level to increase the agreement and the agreement the end of the first of a OSI layer is not necessary.When the data transmission between each floor, each level in the data can be added to the head and tail, and these data have been included to increase the level of the head and tail. Agreement includes the first layer and the communication of information between layers. Head and tail as well as the data is associated with the concept, they depend on the analysis of the protocol layer module. For example, the transport layer header includes only the transport layer can be seen the information, the transport layer of the other layers below this only the first part of a data transmission. For the network layer, an information unit from the third layer composed of the first and data. The data link layer, network layer by passing down all the information that is the first and third data layer is seen as data. In other words, a given OSI layer, the information unit that contains the data from all parts of the upper head and tail, as well as data, referred to as packaging. For example, if computer A to a certain application data sent to computer B, the first data sent to the application layer. A computer in the application layer protocol data to add up and the application layer of computer B communications. Formed by the first information unit includes an agreement, data, and possibly the end of the agreement was sent to that layer, that layer of computer B and then add that layer of the control information to understand the agreement first. Information on the size of units in each level in agreement with the agreement the end of the first and add the increase in the first of these agreements and agreements contained in the computer B the end of the corresponding layers of control information to be used. In the physical layer, the entire information unit through the network transmission medium.Computer B in the physical layer unit of information received and sent to the data link layer; and B data link layer in computer A to read the data link layer protocol header added to the control of information;and then remove the agreement and the end of the first agreement, sent to the remainder of the network layer. Perform the same at every level of action： from the corresponding first layer to read the agreement and protocol tail, and remove, and then send the remaining first floor. End of application-layer implementation of these actions, the data sent to computer B on the application, the data and computer applications A is exactly the same as sent.An OSI layer and another layer of communication between the second layer is the use of the services completed. Services provided by adjacent layers help a OSI layer with another layer corresponds to the computer system to communicate. A particular layer of the OSI model is often associated with three other OSI layers contact: with the layer directly adjacent to and under the floor, as well as the objectives of the corresponding computer systems networking layer. For example, computer A's data link layer should be with the network layer, physical layer of computer B, as well as the data link layer communication.附录B为了让电脑来沟通，就必须讲同样的语言或议定书。
英语科普文选-中英文对照(计算机,互联网,通信)
英语科普文选（中英对照）计算机与因特网插件指南Life on-line can be a much richer experience when you aren't restricted to just written words and still pictures. Even if you're new to the Net, you've probably heard aobut multimediaon-line--listening to audio, watching animations and videos, even playing inthree-dimensional space. Sound and movement make information come alive.To experience it, you'll need special pieces of software called plug-ins. The term "plug-in" refers to a small, add-on piece of software which extends the capabilities of your web browser, like Netscape Navigator or Microsoft Explorer, turning your computer into a radio or TV.When you arrive at a web page which contains a file requiring a plug-in which you don't have, you will usually receive a message asking if you want to get it by downloading it and installing it into your computer. Most of the time, the installation will be automatic.Occasionally, you'll run into a downloaded file which needs to be decompressed orun-zipped before installation. Once installed, plug-ins run automatically, without you having to do anything.Many multimedia controls still need to be obtained from the developer but are installed automatically.Shockwave is a good example of this. All you need to do is go to the Macromedia site and click on the link to install the ActiveX control. The rest happens automatically. The next time you go to a "Shocked" website, the Shockwave control loads and plays the movie.Most plug-ins and controls can be downloaded for free on the Internet, although not all will work with every system. Some of them, for instance, only work with windows95.当你不再仅仅限于文字和静止图片时，网上生活会丰富多彩得多。
计算机网络外文翻译
附录一、英文原文：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 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 webbrowser 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 VaticanMuseum. When you click your mouse on a link, you access the web server for the VaticanMuseum.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 NationalCenter 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 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 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.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 thereason. 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 addressincorrectly.Solution: Check the address and try typing it again.二、英文翻译：网络网络的诞生迄今为止，因特网的历史虽比较简短，但仍然是突破性的。
计算机英文文献加翻译
Management Information System Overview Management Information System is that we often say that the MIS, is a human, computers and other information can be composed of the collection, transmission, storage, maintenance and use of the system, system, emphasizing emphasizing the the management, management, management, stressed stressed stressed that that the modern information society In the increasingly popular. MIS is a new subject, it across a number of areas, such as scientific scientific management management management and and and system system system science, science, science, operations operations operations research, research, research, statistics statistics statistics and and and computer computer science. In these subjects on the basis of formation of information-gathering and processing methods, thereby forming a vertical and horizontal weaving, and systems. The 20th century, along with the vigorous development of the global economy, many economists have proposed a new management theory. In the 1950s, Simon made dependent on information management and decision-making ideas. Wiener published the same period of the control theory, that he is a management control process. 1958, Gail wrote: "The management will lower the cost of timely and accurate information to b etter control." During better control." During this period, accounting for the beginning of the computer, data processing in the term.1970, Walter T . Kenova just to the management information system under a definition of the . Kenova just to the management information system under a definition of the term: "verbal or written form, at the right time to managers, staff and outside staff for the past, present, the projection of future Enterprise and its environment-related information 原文请找腾讯3249114六,维^论~文.网 no no application application application model, model, model, no no mention mention of of computer applications. 1985, management information systems, the founder of the University of Minnesota professor of management at the Gordon B. Davis to a management information system a more complete definition of "management information system is a computer hardware and software resources, manual operations, analysis, planning , Control and decision -making model and the database - System. System. It It provides information to to support support enterprises enterprises or or organizations organizations of of the operation, management and decision-making function. "Comprehensive definition of this Explained Explained that that that the the the goal goal goal of of of management management management information information information system, system, system, functions functions functions and and and composition, composition, composition, but but also reflects the management information system at the time of level.With the continuous improvement of science and technology, computer science increasingly mature, the computer has to be our study and work on the run along. Today, computers are already already very low price, performance, but great progress, and it was used in many areas, the very low price, performance, but great progress, and it was used in many areas, the computer computer was was was so so so popular popular popular mainly mainly mainly because because because of of of the the the following following following aspects: aspects: aspects: First, First, First, the the the computer computer computer can can substitute for many of the complex Labor. Second, the computer can greatly enhance people's work work efficiency. efficiency. efficiency. Third, Third, Third, the the the computer computer computer can can can save save save a a a lot lot lot of of of resources. resources. resources. Fourth, Fourth, Fourth, the the the computer computer computer can can make sensitive documents more secure.Computer application and popularization of economic and social life in various fields. So that the original old management methods are not suited now more and social development. Many people still remain in the previous manual. This greatly hindered the economic development of mankind. mankind. In recent years, with the University of sponsoring scale is In recent years, with the University of sponsoring scale is growing, the number of students students in in in the the the school school school also also also have have have increased, increased, increased, resulting resulting resulting in in in educational educational educational administration administration administration is is is the the growing complexity of the heavy work, to spend a lot of manpower, material resources, and the existing management of student achievement levels are not high, People have been usin g the traditional method of document management student achievement, the management there are many shortcomings, such as: low efficiency, confidentiality of the poor, and Shijianyichang, will have a large number of of documents documents documents and and data, which is is useful useful for finding, finding, updating updating and maintaining Have brought a lot of difficulties. Such a mechanism has been unable to meet the development of the times, schools have become more and more day -to-day management of a bottleneck. bottleneck. In In In the the the information information information age age age this this this traditional traditional traditional management management management methods methods methods will will will inevitably inevitably inevitably be be computer-based information management replaced. As As part part part of of of the the the computer computer computer application, application, application, the the the use use use of of of computers computers computers to to to students students students student student student performance performance information for management, with a manual management of the incomparable advantages for example: example: rapid rapid rapid retrieval, retrieval, retrieval, to to to find find find convenient, convenient, convenient, high high high reliability reliability reliability and and and large large large capacity capacity capacity storage, storage, storage, the the confidentiality confidentiality of of of good, good, good, long long long life, life, life, cost cost cost Low. Low. Low. These These These advantages advantages advantages can can can greatly greatly greatly improve improve improve student student performance management students the efficiency of enterprises is also a scientific, standardized standardized management, management, management, and and and an an an important important important condition condition condition for for for connecting connecting connecting the the the world. world. world. Therefore, Therefore, the development of such a set of management software as it is very necessary thing.Design ideas are all for the sake of users, the interface nice, clear and simple operation as far as possible, but also as a practical operating system a good fault-tolerant, the user can misuse a timely manner as possible are given a warning, so that users timely correction . T o take full advantage advantage of the of the functions of visual FoxPro, design p owerful software powerful software at the same time, as much as possible to reduce the occupiers system resources. Visual FoxPro the command structure and working methods: Visual FoxPro was originally originally called called FoxBASE, FoxBASE, the the U.S. U.S. Fox Fox Software has introduced introduced a a database products, products, in in the run on DOS, compatible with the abase family. Fox Fox Software Software Microsoft acquisition, to be developed so that it can run on Windows, and changed its name to Visual FoxPro. Visual FoxPro is a powerful relational database rapid application development tool, tool, the the the use use use of of of Visual Visual Visual FoxPro FoxPro FoxPro can can can create create create a a a desktop desktop desktop database database database applications, applications, applications, client client client / / / server server applications applications and and and Web Web Web services services services component-based component-based component-based procedures, procedures, procedures, while while while also also also can can can use use use ActiveX ActiveX controls or API function, and so on Ways to expand the functions of Visual FoxPro.1651First, work methods 1. Interactive mode of operation (1) order operation VF in the order window, through an order from the keyboard input of all kinds of ways to complete the operation order. (2) menu operation VF use menus, windows, dialog to achieve the graphical interface features an interactive operation. (3) aid operation VF in the system provides a wide range of user-friendly operation of tools, such as the wizard, design, production, etc.. 2. Procedure means of implementation VF in the implementation of the procedures is to form a group of orders and programming language, an extension to save. PRG procedures in the document, and then run through the automatic implementation of this order documents and award results are displayed. Second, the structure of command 1. Command structure 2. VF orders are usually composed of two parts: The first part is the verb order, also known as keywords, for the operation of the designated order functions; second part of the order clause, for an order that the operation targets, operating conditions and other information . VF order form are as follows: 3. <Order verb> "<order clause>" 4. Order in the format agreed symbols 5. 5. VF in the order form and function of the use of the symbol of the unity agreement, the meaning of VF in the order form and function of the use of the symbol of the unity agreement, the meaning of these symbols are as follows: 6. Than that option, angle brackets within the parameters must be based on their format input parameters. 7. That may be options, put in brackets the parameters under specific requ ests from users choose to enter its parameters. 8. Third, the project manager 9. Create a method 10. command window: CREA T PROJECT <file name> T PROJECT <file name> 11. Project Manager 12. tab 13. All - can display and project management applications of all types of docume nts, "All" tab contains five of its right of the tab in its entirety . 14. Data - management application projects in various types of data files, databases, free form, view, query documents. 15. Documentation - display 原文请找腾讯原文请找腾讯3249114六,维^论~文.网 , statements, documents, labels and other documents. 16. Category - the tab display and project management applications used in the class library documents, including VF's class library system and the user's own design of the library. 17. Code - used in the project management procedures code documents, such as: program files (. PRG), API library and the use of project management for generation of applications (. APP). 18. (2) the work area 19. The project management work area is displayed and management of all types of document window. 20. (3) order button 21. Project Manager button to the right of the order of the work area of the document window to provide command. 22. 4, project management for the use of 23. 1. Order button function 24. New - in the work area window selected certain documents, with new orders button on the new document added to the project management window. 25. Add - can be used VF "file" menu under the "new" order and the "T ools" menu under the "Wizard" order to create the various independent paper added to the project manager, unified organization with management. 26. Laws - may amend the project has been in existence in the various documents, is still to use such documents to modify the design interface. 27. Sports - in the work area window to highlight a specific document, will run the paper.28. Mobile - to check the documents removed from the project. 29. 29. Even Even Even the the the series series series - - - put put put the the the item item item in in in the the the relevant relevant relevant documents documents documents and and and even even even into into into the the the application application executable file. Database System Design :Database design is the logical database design, according to a forthcoming data classification system and the logic of division-level organizations, is user-oriented. Database design needs of various departments of the integrated enterprise archive data and data needs analysis of the relationship between the various data, in accordance with the DBMS. 管理信息系统概要管理信息系统概要管理信息系统就是我们常说的MIS （Management Information System ），是一个由人、计算机等组成的能进行信息的收集、传送、储存、维护和使用的系统，在强调管理，强调信息的现代社会中它越来越得到普及。
计算机外文文献及翻译(SSH)
附录AHistoryDuke, the Java mascotJames Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. Java was originally designed for interactive television, but it was too advanced for the digital cable television industry at the time. The language was initially called Oak after an oak tree that stood outside Gosling's office; it went by the name Green later, and was later renamed Java, from a list of random words.Gosling aimed to implement a virtual machine and a language that had a familiar C/C++ style of notation.Sun Microsystems released the first public implementation as Java 1.0 in 1995. It promised "Write Once, Run Anywhere" (WORA), providing no-cost run-times on popular platforms. Fairly secure and featuring configurable security, it allowed network- and file-access restrictions. Major web browsers soon incorporated the ability to run Java applets within web pages, and Java quickly became popular. With the advent of Java 2 (released initially as J2SE 1.2 in December 1998–1999), new versions had multiple configurations built for different types of platforms. For example, J2EE targeted enterprise applications and the greatly stripped-down version J2ME for mobile applications (Mobile Java). J2SE designated the Standard Edition. In 2006, for marketing purposes, Sun renamed new J2 versions as Java EE, Java ME, and Java SE, respectively.In 1997, Sun Microsystems approached the ISO/IEC JTC1 standards body and later the Ecma International to formalize Java, but it soon withdrew from the process. Java remains a de facto standard, controlled through the Java Community Process. At one time, Sun made most of its Java implementations available without charge, despite their proprietary software status. Sun generated revenue from Java through the selling of licenses for specialized products such as the Java Enterprise System. Sun distinguishes between its Software Development Kit (SDK) and Runtime Environment (JRE) (a subset of the SDK); the primary distinction involves the JRE's lack of the compiler, utility programs, and header files.On November 13, 2006, Sun released much of Java as open source software under the terms of the GNU General Public License (GPL). On May 8, 2007, Sun finished the process, making all of Java's core code available under free software/open-source distribution terms, aside from a small portion of code to which Sun did not hold the copyright.Sun's vice-president Rich Green has said that Sun's ideal role with regards to Java is as an "evangelist." Following Oracle Corporation's acquisition of Sun Microsystems in 2009–2010, Oracle has described itself as the "steward of Java technology with a relentless commitment to fostering a community of participation and transparency".PrinciplesThere were five primary goals in the creation of the Java language:1.It should be "simple, object oriented, and familiar"、2.It should be "robust and secure".3.It should be "architecture neutral and portable"、4.It should execute with "high performance"、5.It should be "interpreted, threaded, and dynamic".Java PlatformMain articles: Java (software platform) and Java Virtual Machine One characteristic of Java is portability, which means that computer programs written in the Java language must run similarly on any supported hardware/operating-system platform. This is achieved by compiling the Java language code to an intermediate representation called Java bytecode, instead of directly to platform-specific machine code. Java bytecode instructions are analogous to machine code, but are intended to be interpreted by a virtual machine (VM) written specifically for the host hardware. End-users commonly use a Java Runtime Environment (JRE) installed on their own machine for standalone Java applications, or in a Web browser for Java applets. Standardized libraries provide a generic way to access host-specific features such as graphics, threading, and networking.A major benefit of using bytecode is porting. However, the overhead of interpretation means that interpreted programs almost always run more slowly than programs compiled to native executables would. Just-in-Time compilers were introduced from an early stage that compile bytecodes to machine code during runtime.ImplementationsSun Microsystems officially licenses the Java Standard Edition platform for Linux, Mac OS X, and Solaris. Although in the past Sun has licensed Java to Microsoft, the license has expired and has not been renewed. Through a network of third-party vendors and licensees, alternative Java environments are available for these and other platforms.Sun's trademark license for usage of the Java brand insists that all implementations be "compatible". This resulted in a legal dispute with Microsoft after Sun claimed that the Microsoft implementation did not support RMI or JNI and had added platform-specific features of their own. Sun sued in 1997, and in 2001 won a settlement of US$20 million, as well as a court order enforcing the terms of the license from Sun. As a result, Microsoft no longer ships Java with Windows, and in recent versions of Windows, Internet Explorer cannot support Java applets without a third-party plugin. Sun, and others, have made available free Java run-time systems for those and other versions of Windows.Platform-independent Java is essential to the Java EE strategy, and an even more rigorous validation is required to certify an implementation. This environment enables portable server-side applications, such as Web services, Java Servlets, and Enterprise JavaBeans, as well as with embedded systems based on OSGi, using Embedded Java environments. Through the new GlassFish project, Sun is working to create a fully functional, unified open source implementation of the Java EE technologies.Sun also distributes a superset of the JRE called the Java Development Kit (commonly known as theJDK), which includes development tools such as the Java compiler, Javadoc, Jar, and debugger.Java performance and garbage collectorsPrograms written in Java have a reputation for being slower and requiring more memory than those written in C. However, Java programs' execution speed improved significantly with the introduction of Just-in-time compilation in 1997/1998 for Java1.1, the addition of language features supporting better code analysis (such as inner classes, StringBuffer class, optional assertions, etc.), and optimizations in the Java Virtual Machine itself, such as HotSpot becoming the default for Sun's JVM in 2000. Currently, Java code has approximately half the performance of C code.Some platforms offer direct hardware support for Java; there are microcontrollers that can run java in hardware instead of a software JVM, and ARM based processors can have hardware support for executing Java bytecode through its Jazelle option. Automatic memory managementJava uses an automatic garbage collector to manage memory in the object lifecycle. The programmer determines when objects are created, and the Java runtime is responsible for recovering the memory once objects are no longer in use. Once no references to an object remain, the unreachable memory becomes eligible to be freed automatically by the garbage collector. Something similar to a memory leak may still occur if a programmer's code holds a reference to an object that is no longer needed, typically when objects that are no longer needed are stored in containers that are still in use. If methods for a nonexistent object are called, a "null pointer exception" is thrown.One of the ideas behind Java's automatic memory management model is that programmers can be spared the burden of having to perform manual memory management. In some languages, memory for the creation of objects is implicitly allocated on the stack, or explicitly allocated and deallocated from the heap. In the latter case the responsibility of managing memory resides with the programmer. If the program does not deallocate an object, a memory leak occurs. If the program attempts to access or deallocate memory that has already been deallocated, the result is undefined and difficult to predict, and the program is likely to become unstable and/or crash. This can be partially remedied by the use of smart pointers, but these add overhead and complexity. Note that garbage collection does not prevent "logical" memory leaks, i.e. those where the memory is still referenced but never used.Garbage collection may happen at any time. Ideally, it will occur when a program is idle. It is guaranteed to be triggered if there is insufficient free memory on the heap to allocate a new object; this can cause a program to stall momentarily. Explicit memory management is not possible in Java.Java does not support C/C++ style pointer arithmetic, where object addresses and unsigned integers (usually long integers) can be used interchangeably. This allows the garbage collector to relocate referencedobjects and ensures type safety and security. As in C++ and some other object-oriented languages, variables of Java's primitive data types are not objects. Values of primitive types are either stored directly in fields (for objects) or on the stack (for methods) rather than on the heap, as commonly true for objects (but see Escape analysis). This was a conscious decision by Java's designers for performance reasons. Because of this, Java was not considered to be a pure object-oriented programming language. However, as of Java 5.0, autoboxing enables programmers to proceed as if primitive types were instances of their wrapper class. Java contains multiple types of garbage collectors. By default, HotSpot uses the Concurrent Mark Sweep collector, also known as the CMS Garbage Collector. However, there are also several other garbage collectors that can be used to manage the Heap. For 90% of applications in Java, the CMS Garbage Collector is good enough.A class that is not declared public may be stored in any .java file. The compiler will generate a class file for each class defined in the source file. The name of the class file is the name of the class, with .class appended. For class file generation, anonymous classes are treated as if their name were the concatenation of the name of their enclosing class, a $, and an integer.The keyword public denotes that a method can be called from code in other classes, or that a class may be used by classes outside the class hierarchy. The class hierarchy is related to the name of the directory in which the .java file is located.The keyword static in front of a method indicates a static method, which is associated only with the class and not with any specific instance of that class. Only static methods can be invoked without a reference to an object. Static methods cannot access any method variables that are not static.The keyword void indicates that the main method does not return any value to the caller. If a Java program is to exit with an error code, it must call System.exit() explicitly.The method name "main" is not a keyword in the Java language. It is simply the name of the method the Java launcher calls to pass control to the program. Java classes that run in managed environments such as applets and Enterprise JavaBean do not use or need a main() method. A java program may contain multiple classes that have main methods, which means that the VM needs to be explicitly told which class to launch from.The main method must accept an array of String objects. By convention, it is referenced as args although any other legal identifier name can be used. Since Java 5, the main method can also use variable arguments, in the form of public static void main(String... args), allowing the main method to be invoked with an arbitrary number of String arguments. The effect of this alternate declaration is semantically identical (the args parameter is still an array of String objects), but allows an alternative syntax for creating and passing the array.The Java launcher launches Java by loading a given class (specified on the command line or as an attribute in a JAR) and starting its public static void main(String[]) method. Stand-alone programs must declare this method explicitly. The String[] args parameter is an array of String objects containing any arguments passed to the class. The parameters to main are often passed by means of a command line.Criticism of JavaA number of criticisms have been leveled at Java programming language for various design choices in the language and platform. Such criticisms include the implementation of generics, the handling of unsigned numbers, the implementation of floating-point arithmetic, and security vulnerabilities.Class librariesJava Platform and Class libraries diagramJava libraries are the compiled bytecodes of source code developed by the JRE implementor to support application development in Java. Examples of these libraries are: The core libraries, which include:Collection libraries that implement data structures such as lists, dictionaries, trees, sets, queues and double-ended queue, or stacksXML Processing (Parsing, Transforming, Validating) librariesSecurityInternationalization and localization librariesThe integration libraries, which allow the application writer to communicate with external systems. These libraries include:The Java Database Connectivity (JDBC) API for database accessJava Naming and Directory Interface (JNDI) for lookup and discoveryRMI and CORBA for distributed application developmentJMX for managing and monitoring applicationsUser interface libraries, which include:The (heavyweight, or native) Abstract Window Toolkit (AWT), which provides GUI components, the means for laying out those components and the means for handling events from those componentsThe (lightweight) Swing libraries, which are built on AWT but provide (non-native) implementations of the AWT widgetryAPIs for audio capture, processing, and playbackA platform dependent implementation of Java Virtual Machine (JVM) that is the means by which the byte codes of the Java libraries and third party applications are executedPlugins, which enable applets to be run in Web browsersJava Web Start, which allows Java applications to be efficiently distributed to end-users across the InternetLicensing and documentation.DocumentationMain article: JavadocJavadoc is a comprehensive documentation system, created by Sun Microsystems, used by many Java developers. It provides developers with anorganized system for documenting their code. Javadoc comments have an extra asterisk at the beginning, i.e. the tags are /** and */, whereas the normal multi-line comment tags comments in Java and C are set off with /* and */.Sun has defined and supports four editions of Java targeting different application environments and segmented many of its APIs so that they belong to one of the platforms. The platforms are:Java Card for smartcards.、Java Platform, Micro Edition(Java ME) —targeting environments with limited resources、Java Platform, Standard Edition (Java SE) — targeting workstation environments、Java Platform, Enterprise Edition (Java EE) — targeting large distributed enterprise or Internet environments. The classes in the Java APIs are organized into separate groups called packages. Each package contains a set of related interfaces, classes and exceptions. Refer to the separate platforms for a description of the packages available.The set of APIs is controlled by Sun Microsystems in cooperation with others through the Java Community Process program. Companies or individuals participating in this process can influence the design and development of the APIs. This process has been a subject of controversy. Sun also provided an edition called PersonalJava that has been superseded by later, standards-based Java ME configuration-profile pairings.JSP ProfileJSP (JavaServer Pages) is initiated by Sun Microsystems, Inc., with many companies to participate in the establishment of a dynamic web page technical standards. JSP technology somewhat similar to ASP technology, it is in the traditional HTML web page document (*. htm, *. html) to insert the Java programming paragraph (Scriptlet) and JSP tag (tag), thus JSP documents (*. jsp). Using JSP development of the Web application is cross-platform that can run on Linux, is also available for other operating systems.JSP technology to use the Java programming language prepared by the category of XML tags and scriptlets, to produce dynamic pages package processing logic. Page also visit by tags and scriptlets exist in the services side of the resources of logic. JSP page logic and web page design and display separation, support reusable component-based design, Web-based application development is rapid and easy.Web server in the face of visits JSP page request, the first implementation of the procedures of, and then together with the results of the implementation of JSP documents in HTML code with the return to the customer. Insert the Java programming operation of the database can be re-oriented websites, in order to achieve the establishment of dynamic pages needed to function.JSP and Java Servlet, is in the implementation of the server, usually returned to the client is an HTML text, as long as the client browser will be able to visit.JSP 1.0 specification of the final version is launched in September 1999, December has introduced 1.1 specifications. At present relatively new is JSP1.2 norms, JSP2.0 norms of the draft has also been introduced.JSP pages from HTML code and Java code embedded in one of the components.The server was in the pages of client requests after the Java code and then will generate the HTML pages to return to the client browser. Java Servlet JSP is the technical foundation and large-scale Web application development needs of Java Servlet and JSP support to complete. JSP with the Java technology easy to use, fully object-oriented, and a platform-independent and secure, mainly for all the characteristics of the Internet. JSP technology strength：(1) time to prepare, run everywhere. At this point Java better than PHP, in addition to systems, the code not to make any changes.(2) the multi-platform support. Basically on all platforms of any development environment, in any environment for deployment in any environment in the expansion. Compared ASP / PHP limitations are obvious. (3) a strong scalability. From only a small Jar documents can run Servlet / JSP, to the multiple servers clustering and load balancing, to multiple Application for transaction processing, information processing, a server to numerous servers, Java shows a tremendous Vitality. (4) diversification and powerful development tools support. This is similar to the ASP, Java already have many very good development tools, and many can be free, and many of them have been able to run on a variety of platforms under. JSP technology vulnerable：(1) and the same ASP, Java is the advantage of some of its fatal problem. It is precisely because in order to cross-platform functionality, in order to extreme stretching capacity, greatly increasing the complexity of the product. (2) Java's speed is class to complete the permanent memory, so in some cases by the use of memory compared to the number of users is indeed a "minimum cost performance." On the other hand, it also needs disk space to store a series of. Java documents and. Class, as well as the corresponding versions of documents.Spring:It all started with a bean.In 1996, the Java programming language was still a young, exciting, up-and- coming platform. Many developers flocked to the language because t hey’d seen how to create rich and dynamic web applications using applets. They soon learned that there was more to this strange new language than animated juggling cartoon characters. Unlike any language before it, Java made it possible to write complex applications made up of discrete parts. They came for the applets, but they stayed for the components. In December of that year, Sun Microsystems published the JavaBeans 1.00-A spec- ification. JavaBeans defined a software component model for Java. This specification defined a set of coding policies that enabled simple Java objects to be reusable and easily composed into more complex applications. Although JavaBeans were intended as a general-purpose means of defining reusable application components they were primarily used as a model for building user interface widgets. They seemed too simple to be capable of any “real” work.Enterprise developers wanted more. Sophisticated applications often require services such as transaction support, secu-rity, and distributed computing—services not directly provided by the JavaBeans spec- ification. So in March 1998, Sun published version 1.0 of the Enterprise JavaBeans (EJB) specification. This specification extended the notion of Java components to the server side, providing much-needed enterprise services, but failed to continue the simplicity of the original JavaBeans specification. Except in name, EJB bears little resemblance to the original JavaBeans specification.Despite the fact that many successful applications have been built based on EJB, EJB never achieved its intended purpose: to simplify enterprise application develop- ment. It’s true that EJB’s declarative programming model simplifies many infrastruc-tural aspects of development, such as transactions and security. But in a different way, EJBs complicate development by mandating deployment descriptors and plumbing code (home and remote/local interfaces). Over time, many developers became disen- chanted with EJB. As a result, its popularity has waned in recent years, leaving many developers looking for an easier way.Today, Java component development has returned to its roots. New programming techniques, including aspect-oriented programming (AOP) and dependency injection (DI), are giving JavaBeans much of the power previously reserved for EJBs. These tech- niques furnish plain-old Java objects (POJOs) with a declarative programming model reminiscent of EJB, but without all of EJB’s complexity. No longer must you resort to writing an unwieldy EJB component when a simple JavaBean will suffice. In fairness, even EJBs have evolved to promote a POJO-based programming model. Employing ideas such as DI and AOP, the latest EJB specification is significantly sim- pler than its predecessors. But for many developers, this move is too little, too late. By the time the EJB 3 specification had entered the scene, other POJO-based develop- ment frameworks had already established themselves as de facto standards in the Java community..Leading the charge for lightweight POJO-based development is the Spring Frame- work。
信息与计算科学中英文对照外文翻译文献
中英文对照外文翻译文献(文档含英文原文和中文翻译)【Abstract】Under the network environment the library information resource altogether constructs sharing is refers to all levels of each kind of library basis user to the social information demand, through network use computer, correspondence, electron, multimedia and so on advanced information technology, the high idealization carries on the synthesis cooperation development and the use activity to various collections information resource and the network resources . The market economy swift and violent development, the networking unceasing renewal, the information age arrival, had decided the future library trend of development will be implements the information resource altogether to construct sharing, already achieved the social mutual recognition about this point.This is because:libraries implement the information resource altogether to construct sharing are solve the knowledge information explosion and the collection strength insufficient this contradictory important way..【Key Words】Network; libraries implement: information: construction；work environment the libraryUnder the network environment the library information resource altogether constructs sharing is refers to all levels of each kind of library basis user to the social information demand, through network use computer, correspondence, electron, multimedia and so on advanced information technology, the high idealization carries on the synthesis cooperation development and the use activity to various collections information resource and the network resources.1、 information resource altogether will construct sharing is the future library development and the use information resource way that must be taken.The market economy swift and violent development, the networking unceasing renewal, the information age arrival, had decided the future library trend of development will be implements the information resource altogether to construct sharing, already achieved the social mutual recognition about this point.This is because: 。
外文文献—计算机网络
英文原文：Computer networkA computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources. Networks may be classified according to a wide variety of characteristics. A computer network allows sharing of resources and information among interconnected devices.History ：Early networks of communicating computers included the military radar system Semi-Automatic Ground Environment (SAGE) and its relative the commercial airline reservation system Semi-Automatic Business Research Environment (SABRE),started in the late 1950s.[1][2]When Russia launched His SPUTNIK Satellite in Space In 1957.The American Started Agency Names ADV ANCE RESEARCH PROJECT AGENCY (ARPA) & launched THis 1st Satellite Within 18 Month After Establishment.Then Sharing Of TheInformation InAnother Computer They Use ARPANET.And This All Responsibility On America's Dr.LIED LIEDER.Then in 1969,ARPANET Comes in INDIA And INDIAN Switched This Name To NETWORK. In the 1960s, the Advanced Research Projects Agency (ARPA) started funding the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. Development of the network began in 1969, based on designs developed during the1960s.[3] The ARPANET evolved into the modern Internet.Purpose ：Computer networks can be used for a variety of purposes: Facilitating communications. Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.Sharing hardware.：In a networked environment, each computer on a network may access and use hardware resources on the network, such as printing a document on a shared network printer.Sharing files, data, and information. In a network environment, authorized user may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.Sharing software.：Users connected to a network may run application programs on remote computers.information preservationSecurityNetwork classification The following list presents categories used for classifying networks.Connection method ：Computer networks can be classified according to thehardware and software technology that is used to interconnect the individual devices in the network, such as optical fiber, Ethernet, wireless LAN, HomePNA, power line communication or G.hn.Ethernet as it is defined by IEEE 802 utilizes various standards and mediums that enable communication between devices. Frequently deployed devices include hubs, switches, bridges, or routers. Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium. ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network.Wired technologies ：Twisted pair wire is the most widely used medium for telecommunication.Twisted-pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer networking cabling consist of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 million bits per second to 100 million bits per second. Twisted pair cabling comes in two forms which are Unshielded Twisted Pair (UTP) and Shielded twisted-pair (STP) which are rated in categories which are manufactured in different increments for various scenarios.Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmissionspeed range from 200 million to more than 500 million bits per second.Optical fiber cable consists of one or more filaments of glass fiber wrapped in protective layers. It transmits light which can travel over extended distances.Fiber-optic cables are not affected by electromagnetic radiation. Transmission speedmay reach trillions of bits per second. The transmission speed of fiber optics is hundreds of times faster than for coaxial cables and thousands of times faster than atwisted-pair wire.[citation needed]Wireless technologies ：Terrestrial microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment looks similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx, 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.Communications satellites –The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relayingvoice, data, and TV signals.Cellular and PCS systems – Use several radio communications technologies. The systems are divided to different geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.Wireless LANs –Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. An example of open-standards wireless radio-wave technology is IEEE.Infrared communication , which can transmit signals between devices within small distances not more than 10 meters peer to peer or ( face to face ) without any body in the line of transmitting.Scale：Networks are often classified as local area network (LAN), wide area network (WAN), metropolitan area network (MAN), personal area network (PAN), virtual private network (VPN), campus area network (CAN), storage area network (SAN), and others, depending on their scale, scope and purpose, e.g., controller area network (CAN) usage, trust level, and access right often differ between these types of networks. LANs tend to be designed for internal use by an organization's internal systems and employees in individual physical locations, such as a building, while WANs may connect physically separate parts of an organization and may include connections to third parties.Functional relationship (network architecture) ：Computer networks may be classified according to the functional relationships which exist amongthe elements of the network,e.g., active networking, client–server, Wireless ad hoc network andpeer-to-peer (workgroup) architecture.Network topology ：Main article: Network topology Computer networks may be classified according to the network topology upon which the network is based, such as bus network, star network, ring network, mesh network.Network topology is the coordination by which devices in the network are arranged in their logical relations to one another, independent of physical arrangement. Even if networked computers are physically placed in a linear arrangement and are connected to a hub, the network has a star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.Types of networks based on physical scopeCommon types of computer networks may be identified by their scale.Local area network：A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on Ethernettechnology, although new standards like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines).[4]Typical library network, in a branching tree topology and controlled access to resources All interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router thatconnects to the Internet and academic networks' customer access routers.The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and no need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 40 and 100 Gbit/s.[5]Personal area network :A personal area network (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters.[6] A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.Home area network :A home area network (HAN) is a residential LAN which is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a CATV or Digital Subscriber Line (DSL) provider. It can also be referred to as an office area network (OAN).Wide area network :A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.Campus network :A campus network is a computer network made up of an interconnection of local area networks (LAN's) within a limited geographical area. The networkingequipments (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc.).In the case of a university campus-based campus network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls.Metropolitan area network:A Metropolitan area network is a large computer network that usually spans a city or alarge campus. Sample EPN made of Frame relay WAN connections and dialup remote access.Enterprise private network :An enterprise private network is a network build by an enterprise to interconnect various company sites, e.g., production sites, head offices, remote offices, shops, in order to share computer resources.Virtual private network :A virtual private network (VPN) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through thelarger network when this is the case. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features.VPN may have best-effort performance, or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point.Internetwork :An internetwork is the connection of two or more private computer networks via a common routing technology (OSI Layer 3) using routers. The Internet is an aggregation of many internetworks, hence its name was shortened to Internet.Backbone network :A Backbone network (BBN) A backbone network or network backbone is part of a computer network infrastructure that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnetworks.[1][2] A backbone can tie together diverse networks in the same building, in different buildings in a campus environment, or over wide areas. Normally, the backbone's capacity is greater than the networks connected to it.A large corporation that has many locations may have a backbone network that ties all of the locations together, for example, if a server cluster needs to be accessed by different departments of a company that are located at different geographical locations.The pieces of the network connections (for example: ethernet, wireless) that bring these departments together is often mentioned as network backbone. Networkcongestion is often taken into consideration while designing backbones. Backbone networks should not be confused with the Internet backbone.Global area network:A global area network (GAN) is a network used for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial wireless LANs.[7]Internet :The Internet is a global system of interconnected governmental, academic, corporate, public, and private computer networks. It is based on the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research ProjectsAgency Network (ARPANET) developed by DARPA of the United States Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW).Intranets and extranets :Intranets and extranets are parts or extensions of a computer network, usually a local area network. An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.An extranet is a network that is limited in scope to a single organization or entity and also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities—a company's customers may be given access to some part of its intranet—while at the same time the customers may not be considered trusted from a security standpoint. Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although an extranet cannot consist of a single LAN; it must have at least one connection with an external network.Overlay network:An overlay network is a virtual computer network that is built on top of another network. Nodes in the overlay are connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network.中文译文：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。
网络设计与规划中英文对照外文翻译文献
网络设计与规划中英文对照外文翻译文献现代企业面临的挑战尽管企业进行了大量的IT资本投资，但许多公司发现，大部分关键网络资源和信息资产仍处于自由状态。
实际上，许多"孤立"的应用程序和数据库无法相互通信，这是一种常见的商业现象。
2.The n: Service-Oriented ork Architecture (SONA)___'___(SONA) ___ is based on a service-oriented architecture (SOA) approach。
___.解决方案：面向服务的网络架构（SONA）___的面向服务的网络架构（SONA）是一个全面的框架，帮助企业克服网络设计和规划的挑战。
SONA基于面向服务的架构（SOA）方法，使企业能够将不同的应用程序和数据库集成到一个统一的网络中。
3.___ SONABy implementing SONA。
businesses ___ of benefits。
___。
increased security。
___。
___ security features。
such as identity and access management。
to protect critical n assets。
Finally。
___.SONA的好处通过实施SONA，企业可以获得许多好处，包括提高网络敏捷性、增加安全性和降低成本。
SONA通过提供灵活和可扩展的网络架构，使企业能够快速适应不断变化的业务需求。
此外，SONA提供了增强的安全功能，如身份和访问管理，以保护关键信息资产。
最后，SONA通过简化网络管理和减少对额外硬件和软件的需求，帮助企业降低成本。
4.nIn today's fast-paced business environment。
it is essential for ___。
secure。
and cost-effective ork architecture.结论在今天快节奏的商业环境中，企业必须拥有一个可以快速适应不断变化的业务需求的网络基础设施。
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。
Internet中英文资料对照外文翻译文献综述
中英文资料对照外文翻译文献综述Internet的历史起源——ARPAnetInternet是被美国政府作为一项工程进行开发的。
这项工程的目的，是为了建立远距离之间点与点的通信，以便处理国家军事范围内的紧急事件，例如核战争。
这项工程被命名为ARPAnet，它就是Internet的前身。
建立此工程的主要应用对象就是军事通讯，那些负责ARPAnet的工程师们当时也没有想到它将成为“Internet”。
根据定义，一个“Internet”应该由四或者更多的计算机连接起来的网络。
ARPAnet是通过一种叫TCP/IP的协议实现连网工作的。
此协议最基础的工作原理是：如果信息在网络中的一条路径发送失败，那么它将找到其他路径进行发送，就好象建立一种语言以便一台计算机与其他计算机“交谈”一样，但不注意它是PC，或是Macintosh。
到了20世纪80年代，ARPAnet已经开始变成目前更为有名的Internet了，它拥有200台在线主机。
国防部很满意ARPAnets的成果，于是决定全力将它培养为能够联系很多军事主机，资源共享的服务网络。
到了1984年，它就已经超过1000台主机在线了。
在1986年ARPAnet关闭了，但仅仅是建立它的机构关闭了，而网络继续存在与超过1000台的主机之间。
由于使用NSF连接失败，ARPAnet才被关闭。
NSF是将5个国家范围内的超级计算机连入ARPAnet。
随着NSF的建立，新的高速的传输介质被成功的使用，在1988年，用户能通过56k的电话线上网。
在那个时候有28，174台主机连入Internet。
到了1989年有80，000台主机连入Internet。
到1989年末，就有290，000台主机连入了。
另外还有其他网络被建立，并支持用户以惊人的数量接入。
于1992年正式建立。
现状——Internet如今，Internet已经成为人类历史上最先进技术的一种。
每个人都想“上网”去体验一下Internet中的信息财富。
计算机网络技术中英文对照外文翻译文献
中英文资料外文翻译网站建设技术1.介绍网络技术的发展,为今天全球性的信息交流与资在建立源共享和交往提供了更多的途径和可能。
足不出户便可以知晓天下大事,按几下键盘或点几下鼠标可以与远在千里之外的朋友交流,网上通信、网上浏览、网上交互、网上电子商务已成为现代人们生活的一部分。
Internet 时代, 造就了人们新的工作和生活方式,其互联性、开放性和共享信息的模式,打破了传统信息传播方式的重重壁垒,为人们带来了新的机遇。
随着计算机和信息时代的到来,人类社会前进的脚步在逐渐加快。
近几年网页设计发展,快得人目不暇接。
随着网页设计技术的发展,丰富多彩的网页成为网上一道亮丽的风景线。
要想设计美观实用的网页就应该深入掌握网站建设技术。
在建立网站时,我们分析了网站建立的目的、内容、功能、结构,应用了更多的网页设计技术。
2、网站的定义2.1 如何定义网站确定网站的任务和目标,是建设网站所面临的最重要的问题。
为什么人们会来到你的网站? 你有独特的服务吗? 人们第一次到你的网站是为了什么? 他们还会再来吗? 这些问题都是定义网站时必须考虑的问题。
要定义网站,首先,必须对整个网站有一个清晰认识,弄清到底要设计什么、主要的目的与任务、如何对任务进行组织与规划。
其次,保持网站的高品质。
在众多网站的激烈竞争中,高品质的产品是长期竞争的最大优势。
一个优秀的网站应具备：（1）用户访问网站的速度要快；（2）注意反馈与更新。
及时更新网站内容、及时反馈用户的要求；（3）首页设计要合理。
首页给访问者留下的第一印象很重要,设计务必精美,以求产生良好的视觉效果。
2.2 网站的内容和功能在网站的内容方面,就是要做到新、快、全三面。
网站内容的类型包括静态的、动态的、功能的和事物处理的。
确定网站的内容是根据网站的性质决定的,在设计政府网站、商业网站、科普性网站、公司介绍网站、教学交流网站等的内容和风格时各有不同。
我们建立的网站同这些类型的网站性质均不相同。
外文翻译--计算机网络1
外文原文Computer NetworksNetwork GoalsSome reasons are causing centralized computer systems to give way to networks.The first one is that many organizations already have a substantial number of computers in operation, often located far apart .Initially, each of these computers may have worked in isolation from the other ones, but at a certain time, and management may have decided to connect them to be able to correlate information about the entire organization. Generally speaking, the goal is to make all programs, data, and other resources available to anyone on the network without regard to the physical location of the resource and the user.The second one is to provider high reliability by having alternative sources of supply. With a network, the temporary loss of a single computer is much less serious, because its users can often be accommodated elsewhere until the service is restored.Another important reason for distributing computing power has to do with the relative price of computing versus communication. Now the cost of a small computer is negligible, so it becomes attractive to analyze the data at where it is captured, and only to send occasional summaries back to the computer center, to reduce the communication cost, which now represents a larger percentage of the total cost than it used to.Yet another reason of setting up a computer network is that a computer network can provider a powerful communication medium among widely separated people.Application of NetworksOne of the main areas of potential network use is access to remote data bases. It may someday be easy for people sitting at their terminalsat home to make reservations for airplanes, trains, bused, boats, restaurants, theaters, hotels, and so on, at anywhere in the world with instant confirmation. Home banking, automated newspaper and fully automated library also fall in this category.Computer aided education is another possible field for using network, with many different coursed being offered.Teleconferencing is a whole new form of communication. With it, widely separated people can conduct a meeting by typing messages at their terminals. Attendees may leave at will, and find out what they missed when they come back. International contacts by human being may be greatly enhanced by network based communication facilities.Network StructureIn any network exists a collection of machines intended to running user (i.e., application) program. These machines are called hosts. The hosts are connected by the communication subnet. The job of the subnet is to carry messages from host to host.The subnet consists of two basic components: nodes and channels. Nodes are specialized computers. All traffic to or from the host goes via its node. Channels are transmission lines.Broadly speaking, there are two general types of designs for the communication subnet:(1)Point-to-point channels(2Broadcast channelsIn the first one, the network contains numerous cables or leased telephone lines, each one connecting a pair of nodes. If two nodes that do not share a cable wish to communicate, they must do this indirectly via other nodes. When a message is sent from one node to another via one or more inter mediate nodes, each intermediate node will receive the message and store it until the required output line is free so that itcan transmit the message forward. The subnet using this principle is called a point-to-point or store-and-forward subnet.When a point-to-point subset is used, the important problem is how to design the interconnected topology between the nodes.The second kind of communication architecture uses broadcasting. In this design there is a single communication channel shared by all nodes. The inherence in broadcast system is that messages sent by any node are received by all other nodes.Protocol HierarchiesTo reduce their design complexity, most networks are organized as a series of layers or levels, each one built upon its predecessor. Layer n on one machine carries on a conversation with layer n on another machine. The rules and conventions used in this conversation are collectively called the layer n protocol. In reality, no data are directly transferred from layer n on one machine to layer n on another machine (except in the lowest layer).Instead, each layer passes data and control information to the following layer immediately, until the lowest layer is reached. At the lowest layer there is one physical communication with the other machine, as opposed to the virtual communication used by the higher layers.Between each pair of adjacent layers there is an interface. The interface defines which primitive operations and services the lower offers to the upper one.The set of layers and protocols is called network architecture. Design Issues for the LayersOne set of design decisions are the rules for data transfer. Do data only travel in one direction, called simplex communication, or travel in either direction, but not simultaneously, called half-duplex communication, or travel in both directions at once, call full-duplexcommunicative?Error control is an important issue when the physical communication circuits are not perfect. Many error-detecting and error-correcting codes are known, but both ends of the connection must agree on what kind of code is being used. In addition, the receiver must have some way of telling the sender which messages have been correctly received and which has not. When there are multiple paths between source and destination, at some points in the hierarchy, a routing decision must be made.The ISO Reference ModelThe Reference Model of Open System Interconnection (OSI), as ISO calls it, has seven layers. The major ones of the principles, from which ISO applied to get the seven layers, are as follows:(1) A layer should be created where a different level of abstractions is needed.(2) Each layer should perform a well defined function.(3) The function of each layer should be chosen with an eye toward defining internationally standardized protocols.(4) The layer boundaries should be chosen to minimize the information flow across the interfaces.(5) The number of layers should be large enough so that distinct functions need not be put together in the same layer without necessity, and small enough so that the architecture will not become out of control. The Physical LayerThe physical layer is concerned with transmitting raw bits over a communication channel. Typical questions here are how many volts should be used to represent an 1 and how many a 0, how many microseconds a bit occupies, whether transmission may proceed simultaneously in both directions, how to establish the initial connection and how to tear town the connection when both sides are finished, how many pins the networkconnector has and what kind of function each pin has. The design issues here largely deal with mechanical, electrical and procedural interfacing to the subnet.The Data Link LayerThe task of the data link layer is to obtain a raw transmission facility and to transform it into a line that appears free of transmission errors to the network layer. It accomplishes this task by breaking the input data up into data frames, transmitting the frames sequentially, and processing the acknowledgment frames sent back by the receiver.Since the physical layer merely accepts and transmits a stream of bits without any regard to meaning or structure, it can create and recognize frame boundaries until the data link layer. This can be accomplished by attaching special bits patterns to the beginning and the end of the frame. But it may produce two problems: one is a noise burst on the line can destroy a frame completely. In this case, the software on the source machine must retransmit the frame. The other is that some mechanism must be employed to let the transmitter know much buffer space the receiver has at the moment.The Network LayerThe network layer controls the operation of subnet. It determines the chief characteristics of the node-host interface, and how packets, the units of information exchanged in this layer, are routed within the subnet.What this layer of software does, basically, is to accept messages from the source host, convert them to packets, and observe the packets to get to the destination. The key design issue is how the route is determined. It could not only base on static table, which are "wired into" the network and rarely changed, but else adopt highly dynamic manner, which can determine each packet again to reflect the current network load.The Transport LayerThe basic function of transport layer is to accept data from the session layer, split it up into smaller units, if necessary, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end.This layer is a true end-to-end layer. In other words, a program on the source machine carries on a conversation with a similar program on the destination machine, using the message headers and control messages. The Session LayerWith the session layer, the user must negotiate to establish a connection with a process on another machine. The connection is usually called a session. A session might be used to allow a user to log into a remote time-sharing system or to transfer a file between two machines. The operation of setting up a session between two processes is often called binding.Another function of the session layer is to manage the session once it has been set up.The Presentation LayerThe presentation layer could be designed to accept ASCII strings as input and produce compressed bit patterns as output. This function of the presentation layer is called text compression.In addition, this layer can also perform other transformations. Encryption to provide security is one possibility. Conversion between character codes, such as ASCII to EBCDIC, might often be useful. More generally, different computer usually have incompatible file formats, so a file conversion option might be useful at times.计算机网络网络目标：第一是许多机构已拥有大量正在工作的计算机，这些计算机通常相距较远。
计算机专业中英文翻译外文翻译文献翻译
英文参考文献及翻译Linux - Operating system of cybertimes Though for a lot of people , regard Linux as the main operating system to make up huge work station group, finish special effects of " Titanic " make , already can be regarded as and show talent fully. But for Linux, this only numerous news one of. Recently, the manufacturers concerned have announced that support the news of Linux to increase day by day, users' enthusiasm to Linux runs high unprecedentedly too. Then, Linux only have operating system not free more than on earth on 7 year this piece what glamour, get the favors of such numerous important software and hardware manufacturers as the masses of users and Orac le , Informix , HP , Sybase , Corel , Intel , Netscape , Dell ,etc. , OK?1.The background of Linux and characteristicLinux is a kind of " free (Free ) software ": What is called free,mean users can obtain the procedure and source code freely , and can use them freely , including revise or copy etc.. It is a result of cybertimes, numerous technical staff finish its research and development together through Inte rnet, countless user is it test and except fault , can add user expansion function that oneself make conveniently to participate in. As the most outstanding one in free software, Linux has characteristic of the following:(1)Totally follow POSLX standard, expand the network operatingsystem of supporting all AT&T and BSD Unix characteristic. Because of inheritting Unix outstanding design philosophy , and there are clean , stalwart , high-efficient and steady kernels, their all key codes are finished by Li nus Torvalds and other outstanding programmers, without any Unix code of AT&T or Berkeley, so Linu x is not Unix, but Linux and Unix are totally compatible.(2)Real many tasks, multi-user's system, the built-in networksupports, can be with such seamless links as NetWare , Windows NT , OS/2 ,Unix ,etc.. Network in various kinds of Unix it tests to be fastest in comparing and assess efficiency. Support such many kinds of files systems as FAT16 , FAT32 , NTFS , Ex t2FS , ISO9600 ,etc. at the same time .(3) Can operate it in many kinds of hardwares platform , including such processors as Alpha , SunSparc , PowerPC , MIPS ,etc., to various kinds of new-type peripheral hardwares, can from distribute on global numerous programmer there getting support rapidly too.(4) To that the hardware requires lower, can obtain very good performance on more low-grade machine , what deserves particular mention is Linux outstanding stability , permitted " year " count often its running times.2.Main application of Linux At present,Now, the application of Linux mainly includes:(1) Internet/Intranet: This is one that Linux was used most at present, it can offer and include Web server , all such Inter net services as Ftp server , Gopher server , SMTP/POP3 mail server , Proxy/Cache server , DNS server ,etc.. Linux kernel supports IPalias , PPP and IPtunneling, these functions can be used for setting up fictitious host computer , fictitious service , VPN (fictitious special-purpose network ) ,etc.. Operating Apache Web server on Linux mainly, the occupation rate of market in 1998 is 49%, far exceeds the sum of such several big companies as Microsoft , Netscape ,etc..(2) Because Linux has outstanding networking ability , it can be usedin calculating distributedly large-scaly, for instance cartoon making , scientific caculation , database and file server ,etc..(3) As realization that is can under low platform fullness of Unix that operate , apply at all levels teaching and research work of universities and colleges extensively, if Mexico government announce middle and primary schools in the whole country dispose Linux and offer Internet service for student already.(4) Tabletop and handling official business appliedly. Application number of people of in this respect at present not so good as Windows of Microsoft far also, reason its lie in Lin ux quantity , desk-top of application software not so good as Windows application far not merely, because the characteristic of the freedom software makes it not almost have advertisement thatsupport (though the function of Star Office is not second to MS Office at the same time, but there are actually few people knowing).3.Can Linux become a kind of major operating system?In the face of the pressure of coming from users that is strengthened day by day, more and more commercial companies transplant its application to Linux platform, comparatively important incident was as follows, in 1998 ①Compaq and HP determine to put forward user of requirement truss up Linux at their servers , IBM and Dell promise to offer customized Linux system to user too. ②Lotus announce, Notes the next edition include one special-purpose edition in Linux. ③Corel Company transplants its famous WordPerfect to on Linux, and free issue. Corel also plans to move the other figure pattern process products to Linux platform completely.④Main database producer: Sybase , Informix , Oracle , CA , IBM have already been transplanted one's own database products to on Linux, or has finished Beta edition, among them Oracle and Informix also offer technical support to their products.4.The gratifying one is, some farsighted domestic corporations have begun to try hard to change this kind of current situation already. Stone Co. not long ago is it invest a huge sum of money to claim , regard Linux as platform develop a Internet/Intranet solution, regard this as the core and launch Stone's system integration business , plan to set up nationwide Linux technical support organization at the same time , take the lead to promote the freedom software application and development in China. In addition domestic computer Company , person who win of China , devoted to Linux relevant software and hardware application of system popularize too. Is it to intensification that Linux know , will have more and more enterprises accede to the ranks that Linux will be used with domestic every enterprise to believe, more software will be planted in Linux platform. Meanwhile, the domestic university should regard Linux as the original version and upgrade already existing Unix content of courses , start with analysing the source code and revising the kernel and train a large number of senior Linux talents, improve our country's own operating system. Having only really grasped the operating system, the software industry of our country could be got rid of and aped sedulously at present, the passive state led by the nose by others, create conditions for revitalizing the software industry of our country fundamentally.中文翻译Linux—网络时代的操作系统虽然对许多人来说，以Linux作为主要的操作系统组成庞大的工作站群，完成了《泰坦尼克号》的特技制作，已经算是出尽了风头。
计算机毕业论文外文文献翻译中英文：IEEE802.11媒体接入控制
计算机毕业论⽂外⽂⽂献翻译中英⽂：IEEE802.11媒体接⼊控制英⽂资料与中⽂翻译IEEE 802.11 MEDIUM ACCESS CONTROLThe IEEE 802.11 MAC layer covers three functional areas：reliable data delivery, medium access control, and security. This section covers the first two topics.Reliable Data DeliveryAs with any wireless network, a wireless LAN using the IEEE 802.11 physical and MAC layers is subject to considerable unreliability. Noise, interference, and other propagation effects result in the loss of a significant number of frames. Even with error-correction codes, a number of MAC frames may not successfully be received. This situation can be dealt with by reliability mechanisms at a higher layer. such as TCP. However, timers used for retransmission at higher layers are typically on the order of seconds. It is therefore more efficient to deal with errors at the MAC level. For this purpose, IEEE 802.11 includes a frame exchange protocol. When a station receives a data frame from another station. It returns an acknowledgment (ACK) frame to the source station. This exchange is treated as an atomic unit, not to be interrupted by a transmission from any other station. If the source does not receive an ACK within a short period of time, either because its data frame was damaged or because the returning ACK was damaged, the source retransmits the frame.Thus, the basic data transfer mechanism in IEEE802.11 involves an exchange of two frames. To further enhance reliability, a four-frame exchange may be used. In this scheme, a source first issues a request to send (RTS) frame to the destination. The destination then responds with a clear to send (CTS). After receiving the CTS, the source transmits the data frame, and the destination responds with an ACK. The RTS alerts all stations that are within reception range of the source that an exchange is under way; these stations refrain from transmission in order to avoid a collision between two frames transmitted at the same time. Similarly, the CTS alerts all stations that are within reception range of the destination that an exchange is under way. The RTS/CTS portion of the exchange is a required function of the MAC but may be disabled.Medium Access ControlThe 802.11 working group considered two types of proposals for a MAC algorithm: distributed access protocols, which, like Ethernet, distribute the decision to transmit over all the nodes using a carrier-sense mechanism; and centralized access protocols, which involve regulation of transmission by a centralized decision maker. A distributed access protocol makes sense for an ad hoc network of peer workstations (typically an IBSS) and may also be attractive in other wireless LAN configurations that consist primarily of burst traffic. A centralized access protocol is natural for configurations in which a umber of wireless stations are interconnected with each other and some sort of base station that attaches to a backbone wired LAN: it is especially useful if some of the data is time sensitive or high priority.The end result for 802.11 is a MAC algorithm called DFWMAC (distributed foundation wireless MAC) that provides a distributed access control mechanism with an optional centralized control built on top of that. Figure 14.5 illustrates the architecture. The lower sub-layer of the MAC layer is the distributed coordination function (DCF). DCF uses a contention algorithm to provide access to all traffic. Ordinary asynchronous traffic directly uses DCE. The point coordination function (PCF) is a centralized MAC algorithm used to provide contention-free service. PCF is built on top of DCF and exploits features of DCF to assure access for its users. Let us consider these two sub-layers in turn.MAClayerFigure 14.5 IEEE 802.11 Protocol ArchitectureDistributed Coordination FunctionThe DCF sub-layer makes use of a simple CSMA (carrier sense multiple access) algorithm, which functions as follows. If a station has a MAC frame to transmit, it listens to the medium. If the medium is idle, the station may transmit; otherwise the station must wait until the current transmission is complete before transmitting. The DCF does not include a collision detection function (i.e. CSMA/CD) because collision detection is not practical on a wireless network. The dynamic range ofthe signals on the medium is very large, so that a transmitting station cannot effectively distinguish incoming weak signals from noise and the effects of its own transmission.To ensure the smooth and fair functioning of this algorithm, DCF includes a set of delays that amounts to a priority scheme. Let us start by considering a single delay known as an inter-frame space (IFS). In fact, there are three different IFS values, but the algorithm is best explained by initially ignoring this detail. Using an IFS, the rules for CSMA access are as follows (Figure 14.6):Figure 14.6 IEEE 802.11 Medium Access Control Logic1. A station with a frame to transmit senses the medium. If the medium is idle. It waits to see if the medium remains idle for a time equal to IFS. If so , the station may transmit immediately.2. If the medium is busy (either because the station initially finds the medium busy or because the medium becomes busy during the IFS idle time), the station defers transmission and continues to monitor the medium until the current transmission is over.3. Once the current transmission is over, the station delays another IFS. If the medium remains idle for this period, then the station backs off a random amount of time and again senses the medium. If the medium is still idle, the station may transmit. During the back-off time, if the medium becomes busy, the back-off timer is halted and resumes when the medium becomes idle.4. If the transmission is unsuccessful, which is determined by the absence of an acknowledgement, then it is assumed that a collision has occurred.To ensure that back-off maintains stability, a technique known as binary exponential back-off is used. A station will attempt to transmit repeatedly in the face of repeated collisions, but after each collision, the mean value of the random delay is doubled up to some maximum value. The binary exponential back-off provides a means of handling a heavy load. Repeated failed attempts to transmit result in longer and longer back-off times, which helps to smooth out the load. Without such a back-off, the following situation could occur. Two or more stations attempt to transmit at the same time, causing a collision. These stations then immediately attempt to retransmit, causing a new collision.The preceding scheme is refined for DCF to provide priority-based access by the simple expedient of using three values for IFS:●SIFS (short IFS):The shortest IFS, used for all immediate responseactions，as explained in the following discussion●PIFS (point coordination function IFS):A mid-length IFS, used by thecentralized controller in the PCF scheme when issuing polls●DIFS (distributed coordination function IFS): The longest IFS, used as aminimum delay for asynchronous frames contending for access Figure 14.7a illustrates the use of these time values. Consider first the SIFS.Any station using SIFS to determine transmission opportunity has, in effect, the highest priority, because it will always gain access in preference to a stationwaiting an amount of time equal to PIFS or DIFS. The SIFS is used in the following circumstances：●Acknowledgment (ACK): When a station receives a frame addressed onlyto itself (not multicast or broadcast) it responds with an ACK frame after, waiting on1y for an SIFS gap. This has two desirable effects. First, because collision detection IS not used, the likelihood of collisions is greater than with CSMA/CD, and the MAC-level ACK provides for efficient collision recovery. Second, the SIFS can be used to provide efficient delivery of an LLC protocol data unit (PDU) that requires multiple MAC frames. In this case, the following scenario occurs. A station with a multi-frame LLC PDU to transmit sends out the MAC frames one at a time. Each frame is acknowledged after SIFS by the recipient. When the source receives an ACK, it immediately (after SIFS) sends the next frame in the sequence. The result is that once a station has contended for the channel, it will maintain control of the channel until it has sent all of the fragments of an LLC PDU.●Clear to Send (CTS):A station can ensure that its data frame will getthrough by first issuing a small. Request to Send (RTS) frame. The station to which this frame is addressed should immediately respond with a CTS frame if it is ready to receive. All other stations receive the RTS and defer using the medium.●Poll response: This is explained in the following discussion of PCF.longer than DIFS(a) Basic access methoddefers(b) PCF super-frame constructionFigure 14.7 IEEE 802.11 MAC TimingThe next longest IFS interval is the: PIFS. This is used by the centralized controller in issuing polls and takes precedence over normal contention traffic. However, those frames transmitted using SIFS have precedence over a PCF poll.Finally, the DIFS interval is used for all ordinary asynchronous traffic.Point C00rdination Function PCF is an alternative access method implemented on top of the DCE. The operation consists of polling by the centralized polling master (point coordinator). The point coordinator makes use of PIFS when issuing polls. Because PI FS is smaller than DIFS, the point coordinator call seize the medium and lock out all asynchronous traffic while it issues polls and receives responses.As an extreme, consider the following possible scenario. A wireless network is configured so that a number of stations with time, sensitive traffic are controlled by the point coordinator while remaining traffic contends for access using CSMA. The point coordinator could issue polls in a round—robin fashion to all stations configured for polling. When a poll is issued, the polled station may respond using SIFS. If the point coordinator receives a response, it issues another poll using PIFS. If no response is received during the expected turnaround time, the coordinator issues a poll．If the discipline of the preceding paragraph were implemented, the point coordinator would lock out all asynchronous traffic by repeatedly issuing polls. To prevent this, an interval known as the super-frame is defined. During the first part of this interval, the point coordinator issues polls in a round, robin fashion to all stations configured for polling. The point coordinator then idles for the remainder of the super-frame, allowing a contention period for asynchronous access.Figure l4.7 b illustrates the use of the super-frame. At the beginning of a super-frame, the point coordinator may optionally seize control and issues polls for a give period of time. This interval varies because of the variable frame size issued by responding stations. The remainder of the super-frame is available for contention based access. At the end of the super-frame interval, the point coordinator contends for access to the medium using PIFS. If the medium is idle. the point coordinator gains immediate access and a full super-frame period follows. However, the medium may be busy at the end of a super-frame. In this case, the point coordinator must wait until the medium is idle to gain access: this result in a foreshortened super-frame period for the next cycle.OctetsFC=frame control SC=sequence controlD/I=duration/connection ID FCS=frame check sequence（a ） MAC frameBitsDS=distribution systemMD=more data MF=more fragmentsW=wired equivalent privacy RT=retryO=orderPM=power management (b) Frame control filedFigure 14.8 IEEE 802.11 MAC Frame FormatMAC FrameFigure 14.8a shows the 802.11 frame format when no security features are used. This general format is used for all data and control frames, but not all fields are used in all contexts. The fields are as follows:● Frame Control: Indicates the type of frame and provides contr01information, as explained presently.● Duration/Connection ID: If used as a duration field, indicates the time(in-microseconds) the channel will be allocated for successful transmission of a MAC frame. In some control frames, this field contains an association, or connection, identifier.●Addresses: The number and meaning of the 48-bit address fields dependon context. The transmitter address and receiver address are the MAC addresses of stations joined to the BSS that are transmitting and receiving frames over the wireless LAN. The service set ID (SSID) identifies the wireless LAN over which a frame is transmitted. For an IBSS, the SSID isa random number generated at the time the network is formed. For awireless LAN that is part of a larger configuration the SSID identifies the BSS over which the frame is transmitted: specifically, the SSID is the MAC-level address of the AP for this BSS (Figure 14.4). Finally the source address and destination address are the MAC addresses of stations, wireless or otherwise, that are the ultimate source and destination of this frame. The source address may be identical to the transmitter address and the destination address may be identical to the receiver address.●Sequence Control: Contains a 4-bit fragment number subfield used forfragmentation and reassembly, and a l2-bit sequence number used to number frames sent between a given transmitter and receiver.●Frame Body: Contains an MSDU or a fragment of an MSDU. The MSDUis a LLC protocol data unit or MAC control information.●Frame Check Sequence: A 32-bit cyclic redundancy check. The framecontrol filed, shown in Figure 14.8b, consists of the following fields.●Protocol Version: 802.11 version, current version 0.●Type: Identifies the frame as control, management, or data.●Subtype: Further identifies the function of frame. Table 14.4 defines thevalid combinations of type and subtype.●To DS: The MAC coordination sets this bit to 1 in a frame destined to thedistribution system.●From DS: The MAC coordination sets this bit to 1 in a frame leaving thedistribution system.●More Fragments: Set to 1 if more fragments follow this one.●Retry: Set to 1 if this is a retransmission of a previous frame.●Power Management: Set to]if the transmitting station is in a sleep mode.●More Data: Indicates that a station has additional data to send. Each blockof data may be sent as one frame or a group of fragments in multiple frames.●WEP：Set to 1 if the optional wired equivalent protocol is implemented.WEP is used in the exchange of encryption keys for secure data exchange.This bit also is set if the newer WPA security mechanism is employed, as described in Section 14.6.●Order：Set to 1 in any data frame sent using the Strictly Ordered service,which tells the receiving station that frames must be processed in order. We now look at the various MAC frame types. Control Frames Control frames assist in the reliable delivery of data frames. There are six control frame subtypes:●Power Save-Poll (PS-Poll): This frame is sent by any station to the stationthat includes the AP (access point). Its purpose is to request that the AP transmit a frame that has been buffered for this station while the station was in power saving mode.●Request to Send (RTS):This is the first frame in the four-way frameexchange discussed under the subsection on reliable data delivery at the beginning of Section 14.3.The station sending this message is alerting a potential destination, and all other stations within reception range, that it intends to send a data frame to that destination.●Clear to Send (CTS): This is the second frame in the four-way exchange.It is sent by the destination station to the source station to grant permission to send a data frame.●Acknowledgment:Provides an acknowledgment from the destination tothe source that the immediately preceding data, management, or PS-Poll frame was received correctly.●Contention-Free (CF)-End: Announces the end of a contention-freeperiod that is part of the point coordination function.●CF-End+CF-Ack:Acknowledges the CF-End. This frame ends thecontention-free period and releases stations from the restrictions associated with that period.Data Frames There are eight data frame subtypes, organized into two groups. The first four subtypes define frames that carry upper-level data from the source station to the destination station. The four data-carrying frames are as follows: ●Data: This is the simplest data frame. It may be used in both a contentionperiod and a contention-free period.●Data+CF-Ack: May only be sent during a contention-free period. Inaddition to carrying data, this frame acknowledges previously received data.●Data+CF-Poll: Used by a point coordinator to deliver data to a mobilestation and also to request that the mobile station send a data frame that it may have buffered.●Data+CF-Ack+CF-Poll: Combines the functions of the Data+CF-Ack andData+CF-Poll into a single frame.The remaining four subtypes of data frames do not in fact carry any user data. The Null Function data frame carries no data, polls, or acknowledgments. It is used only to carry the power management bit in the frame control field to the AP, to indicate that the station is changing to a low-power operating state. The remaining three frames (CF-Ack, CF-Poll,CF-Ack+CF-Poll) have the same functionality as the corresponding data frame subtypes in the preceding list (Data+CF-Ack, Data+CF-Poll,Data+CF-Ack+CF-Poll) but withotit the data. Management FramesManagement frames are used to manage communications between stations and APs. The following subtypes are included:●Association Request：Sent by a station to an AP to request an association,with this BSS. This frame includes capability information, such as whether encryption is to be used and whether this station is pollable.●Association Response:Returned by the AP to the station to indicatewhether it is accepting this association request.●Reassociation Request: Sent by a station when it moves from one BSS toanother and needs to make an association with tire AP in the new BSS. The station uses reassociation rather than simply association so that the new AP knows to negotiate with the old AP for the forwarding of data frames.●Reassociation Response:Returned by the AP to the station to indicatewhether it is accepting this reassociation request.●Probe Request: Used by a station to obtain information from anotherstation or AP. This frame is used to locate an IEEE 802.11 BSS.●Probe Response: Response to a probe request.●Beacon: Transmitted periodically to allow mobile stations to locate andidentify a BSS.●Announcement Traffic Indication Message: Sent by a mobile station toalert other mobile stations that may have been in low power mode that this station has frames buffered and waiting to be delivered to the station addressed in this frame.●Dissociation: Used by a station to terminate an association.●Authentication：Multiple authentication frames are used in an exchange toauthenticate one station to another.●Deauthentication:Sent by a station to another station or AP to indicatethat it is terminating secure communications.IEEE802.11 媒体接⼊控制IEEE 802．11 MAC层覆盖了三个功能区：可靠的数据传送、接⼊控制以及安全。
计算机专业b-s模式 外文翻译 外文文献 英文文献 中英对照
外文翻译ENGLISHE：Develop Web application program using ASP the architecture that must first establish Web application. Now in application frequently with to have two: The architecture of C/S and the architecture of B/S.Client/server and customer end / server hold the architecture of C/S.The customer / server structure of two floor.Customer / server ( Client/Server ) model is a kind of good software architecture, it is the one of best application pattern of network. From technology, see that it is a logic concept, denote will a application many tasks of decomposing difference carry out , common completion is entire to apply the function of task. On each network main computer of web site, resource ( hardware, software and data ) divide into step, is not balanced, under customer / server structure, without the client computer of resource through sending request to the server that has resource , get resource request, so meet the resource distribution in network not balancedness. With this kind of structure, can synthesize various computers to cooperate with work, let it each can, realize the scale for the system of computer optimization ( Rightsizing ) with scale reduce to melt ( Downsizing ). Picture is as follows:It is most of to divide into computer network application into two, in which the resource and function that part supports many users to share , it is realized by server; Another part faces every user , is realized by client computer, also namely, client computer is usual to carry out proscenium function , realizes man-machine interaction through user interface , or is the application program of specific conducted user. And server usually carries out the function of backstage supporter , manages the outside request concerning seting up, accepting and replying user that shared. For a computer, it can have double function , is being certain and momentary to carve to act as server , and again becomes client computer in another time.Customer / server type computer divide into two kinds, one side who offers service is called as server , asks one side of service to be called as customer. To be able to offer service, server one side must have certain hardware and corresponding server software; Also, customer one side mustalso have certain hardware and corresponding customer software.There must be a agreement between server and customer, both sides communicate according to this agreement.Apply customer / server model in Internet service , the relation between customer and server is not immutable. Some Internet node offers service on the one hand , also gets service on the other hand from other node; It is even in one time dialogue course, mutual role also exchanges probably. As in carry out file transmission , if be called as one side who offers file server, is called as one side who gets file customer, when using get or mget order since another node takes file, can think that what self use and it is client computer , is using put or mput order to another node dispatch file can again think the machine that used self is server.Multilayer customer / server structureAlong with the development of enterprise application, recently, have again arisen a kind of new multilayer architecture, it applies customer end to divide into two minutes: Customer application and server apply. Customer application is the part of original customer application , is another and partial to have been transfered to server to apply. New customer application takes the responsibility for user interface and simple regular business logic and new server application resident core , changeable business logic. Therefore its structure has become new ( Client application + Server application )/Server structure. Following picture shows:This kind of structure has solved traditional Client/Server can expand problem, have reduced customer end business logic , and have reduced the requirement of customer end for hardware. At the same time because of a lot of business logic concentrations have gone to unitary application server on, the maintenance work of application system had been also concentrated together, have eliminated the problem in the traditional structure of Client/Server that software distributes. This kind of structure is called as the architecture of B/S.Browser/Server and browser / server hold the architecture of B/S. Onessence, Browser/Server is also a kind of structure of Client/Server, it is a kind of from the traditional two levels of structural development of Client/Server come to the three-layer structural special case of Client/Server that applied on Web.In the system of Browser/Server, user can pass through browser to a lot of servers that spread on network to send request. The structure of Browser/Server is maximum to have simplified the work of client computer, on client computer, need to install and deploy few customer end software only , server will bear more work, for database visit and apply program carry out will in server finish.Under the three-layer architecture of Browser/Server, express layer ( Presentatioon ) , function layer ( Business Logic ) , data layer ( Data Service ) have been cut the unit of 3 relative independences: It is the first layer of to express layer: Web browser.In expressing layer contain system show logic, locate in customer end. It's task is to suggest by Web browser to the certain a Web server on network that service is asked , after verifying for user identity, Web server delivers needed homepage with HTTP agreement to customer end, client computer accept the homepage file that passed , and show it in Web browser on.Second layer function layer: Have the Web server of the application function of program extension.In function layer contain the systematic handling of general affairs logic, locate in Web server end. It's task is the request concerning accepting user , need to be first conducted and corresponding to expand application program and database to carry out connection , passes through the waies such as SQL to database server to put forward data handling to apply for, then etc. database server the result of handling data submit to Web server, deliver again by Web server to return customer end.The number of plies of 3th according to layer: Database server.In data layer contain systematic data handling logic, locate in database server end. It's task is to accept the request that Web server controls for database, realization is inquired and modified for database , update etc. function, submit operation result to Web server.Careful analysis is been easy to see , the architecture of Browser/Server of three-layer is the handling of general affairs of the two levels of structure of Client/Server logic modular from the task of client computer in split , from the first floor of individual composition bear the pressure of its task and such client computer have alleviated greatly, distribute load balancedly and have given Web server, so from the structural change of Client/server of original two floor the structure of Browser/Server of three-layer. This kind of three-layer architecture following picture shows.This kind of structure not only client computer from heavy burden andthe requirement of performance that rises continuously for it in liberation come out , also defend technology people from heavy maintenance upgrading work in free oneself. Since client computer handles general affairs , logic partial minutes have given function server, make client computer right off " slender " a lot of, do not take the responsibility for handling complex calculation and data again visit etc. crucial general affairs, is responsible to show part, so, maintenance people do not rush about again for the maintenance work of program between every client computer, and put major energy in the program on function server update work. Between this kind of three-layer structural layer and layer, the mutually independent change of any first floor does not affect the function of other layer. It has changed the defect of the two levels of architecture of Client/Server of tradition from foundation, it is the transform with deep once in application systematic architecture.The contrast of two architecturesThe architecture of Browser/Server and the architecture ofClient/Server compare with all advantages that not only have the architecture of Client/Server and also have the architecture ofClinet/Server the unique advantage that place does not have: Open standard: The standard adopted by Client/Server only in department unification for but, it's application is often for special purpose.It is lower to develop and defend cost: It need to be implemented on all client computers that the application of Client/Server must develop the customer end software for special purpose, no matter installation and disposition escalate still, have wasted manpower and material resources maximumly. The application of Browser/Server need in customer end have general browser , defend and escalate to work in server end go on , need not carry out any change as customer holds , have reduced the cost of development and maintenance so greatly.It is simple to use , interface friendly: The interface of the user of Client/Server is decided by customer end software, interface and the method of its use are not identical each, per popularize a system of Client/Server ask user study from the beginning, is hard to use. The interface of the user of Browser/Server is unified on browser, browser is easy to use , interface friendly, must not study use again other software, the use of a Lao Yong Yi that has solved user problem.Customer end detumescence: The customer end of Client/Server has the function that shows and handles data , as the requirement of customer end is a client computer " it is fat " very high. The customer of Browser/Server holds the access that not takes the responsibility for database again and the etc. task of complex data calculation, need it only show , the powerful role that has played server fully is so large to have reduced the requirement for customer end, customer end become very " thin ".System is flexible: The 3 minutes of the system of Client/Server, in modular, have the part that need to change to want relation to the change of other modular, make system very difficult upgrading. The 3 minutes of the system of Browser/Server modular relative independence, in which a part of modular change, other modular does not get influence, it is very easy that system improve to become, and can form the system with much better performance with the product of different manufacturer.Ensure systematic safety: In the system of Client/Server, directly join with database server because of client computer, user can very easily change the data on server, can not guarantee systematic safety. The system of Browser/Server has increased a level of Web server between client computer and database server , makes two not to be directly linked again, client computer can not be directly controled for database, prevent user efficiently invade illegally.The architecture of Browser/Server of three-layer has the advantage that a lot of traditional architectures of Client/Server does not have , and is close to have combined the technology of Internet/Intranet, is that the tendency of technical development tends to , it application system tape into one brand-new develop times. From this us option the configuration of B/S the architecture that develops as system.what are C/S with B/SFor " C/S " with the technology of " B/S " develop change know , first,must make it clear that 3 problems.( 1 ) What is the structure of C/S.C/S ( Client/Server ) structure, the server structure and client computer that all know well. It is software systematic architecture, through it can hold hardware environment fully using two advantage, realize task reasonable distribution to Client end and Server end , have reduced systematic communication expense. Now, the most systems of application software are the two levels of structure of the form of Client/Server , are developing to the Web application of distribution type since current software application is systematic, Web and the application of Client/Server can carry out same business handling , apply different modular to share logic assembly; Therefore it is systematic that built-in and external user can visit new and existing application , through the logic in existing application system, can expand new application system. This is also present application system develop direction. Traditional C ／S architecture though adopting is open pattern, but this is the openness that system develops a level , in specific application no matter Client end orServer end the software that need to still specify support. Because of the software software that need to develop different edition according to the different system of operating system that can not offer the structure of C/S and the open environment of user genuine expectation , besides, the renovation of product is very rapid, is nearly impossible to already meet the 100 computer above users of local area network at the same time use. Price has low efficiency high. If my courtyard uses , Shanghai exceed the orchid company's management software " statistics of law case" is typical C ／S architecture management software.( 2 ) What is the structure of B/S.B/S ( Browser/Server ) structure browser and server structure. It is along with the technology of Internet spring up , it is for the structure of improvement or a kind of change of the structure of C/S. Under this kind of structure, user working interface is to realize through WWW browser, lose the logic of general affairs very much in front( Browser) realization, but the major logic of general affairs in server end( Server) realization, form the three-layer claimed 3-tier structure. So, have simplified customer end computer load greatly , have alleviated system to defend workload and the cost with upgrading , have reduced the overall cost of user ( TCO ). With present technology see , local area network the network application that establishes the structure of B/S , and under the pattern of Internet/Intranet, database application is easy to hold relatively , cost also is lower. It is that oneness goes to the development of position , can realize different people, never same place, with difference receive the way of entering ( for example LAN, WAN, Internet/Intranet etc.) visit and operate common database; It can protect data platform efficiently with management visit limits of authority, server database is also safe. Now in my courtyard, net ( Intranet ) , outer net ( Internet ) with Beijing eastern clear big company " law case and the management software of official business " is the structural management software of B/S , policemen each working station in local area network pass through WWW browser can realize working business. Especially in JAVA step platform language appearance after, the configuration management software of B/S is more facilitated , is shortcut, efficient.( 3 ) The management software technology of main stream.The technology of main stream of management software technology is as management thought , have also gone through 3 develop period. First, interface technology goes to Windows graph interface ( or graph user interface GUI ) from last century DOS character interface, till Browser browser interface 3 differences develop period. Secondly, today own the browser interface of computer, is not only visual and is easy to use , what is more major is that any its style of application software based on browser platform is as, make the requirement of choosing a person for the job for operating training not high and software operability is strong , is easy to distinguish; Moreover platform architecture the file that also goes to today from past single user development ／server ( F ／S ) system and client computer ／server ( C ／S ) system and browser ／server ( B ／S ) system.The comparison of C/S and B/SC/S and B/S is the now world two technologies of main stream of developing pattern technical configuration. C/S is that American Borland company researches and develop most early, B/S is that American Microsoft researches and develop. Now this two technologies with quilt world countries grasp , it is many that domestic company produce article with C/S and the technical development of B/S. This two technologies have the certain market share of self , is with customer crowd , each domestic enterprise says that own management software configuration technical function is powerful, advanced, convenient , the customer group that can lift , have a crowd scholar ink guest to shake flag self cry out , advertisement flies all over the sky , may be called benevolent to see kernel, sage sees wisdomC/S configures inferior position and the advantage of software( 1 ) Application server operation data load is lightcomparatively.The database application of the most simple architecture of C/S is become by two partial groups, customer applies program and database server program. Both can be called as proscenium program and the program of backstage supporter respectively. The machine of operation database server program is also called as application server. Once server program had been started , waits the request concerning responding customer program hair at any time; Customer application program operation can becalled as customer computer on the own computer of user, in correspondence with database server, when needs carry out any operation for the data in database, customer program seeks server program voluntarily , and sends request to it, server program is regular as basis intends to make to reply, send to return result, application server operation data load is lighter.( 2 ) Data store management function relatively transparent.In database application data store management function, is carried out respectively independently by server program and customer application program , is regular as proscenium application can violate , and usually those different( no matter is have known still unknown ) operations data, in server program, do not concentrate realization, for instance visit limits of authority, serial number can be repeated , must have customer talent establishment the rule order. It is these to own , for the last user that works on proscenium program is " transparent ", they need not be interest in ( can not usually also interfere ) the course of behind, can complete own all work. In the application of customer server configuration proscenium program not is very " thin ", troublesome matter is delivered to server and network. In the system of C/S take off , database can not become public really , professionally more competent storehouse, it gets independent special management.( 3 ) The inferior position of the configuration of C/S is high maintenance cost make investment just big.First, with the configuration of C/S, will select proper database platform to realize the genuine "unification" of database data, make the data synchronism that spreads in two lands complete deliver by database system go to manage, but the logically two operators of land will directly visit a same database to realize efficiently , have so some problems, if needs establishment the data synchronism of " real time ", the database server that must establish real time communication connection between two places and maintains two lands is online to run , network management staff will again want to defend and manage for customer end as server defends management , maintenance and complex tech support and the investment of this high needs have very high cost, maintenance task is measured.Secondly, the software of the structure of C/S of tradition need to develop thesoftware of different edition according to the different system of operating system , is very rapid because of the renovation of product, price is working needs high with inefficient already do not meet. In JAVA step platform language appearance after, the configuration of B/S is more vigorous impact C/S , and forms threat and challenge for it. .The advantage of B/S configuration software( 1 ) The Maintenance of inferior position and upgrading way are simple.Now upgrading and the improvement of software system more and more frequently, the product of the configuration of B/S embodies more convenient property obviously. For one a little a little bit big unit , if systematic administrator needs , between hundreds of 1000 even last computers round trip run , efficiency and workload is to can imagine, but the configuration of B/S software needs management server have been all right , all customer ends are browser only, need not do any maintenance at all. No matter the scale of user has , is what , has how many branch will not increase any workload of maintenance upgrading , is all to operate needs to aim at server to go on; If need differently only, net server connection specially , realize long-range maintenance and upgrading and share. So client computer more and more " thin ", and server more and more " fat " is the direction of main stream of future informative development. In the future, software upgrading and maintenance will be more and more easy , and use can more and more simple, this is for user manpower , material resources, time and cost save is obvious , it is astonishing. Therefore defend and escalate revolutionary way is the client computer " it is thin ", " is fat " server.( 2 ) Cost reduction, it is more to select.All know windows in the computer of top of a table on nearly one Tong world, browser has become standard disposition, but on server operating system, windows is in absolute dominance position not. Current tendency is the application management software that uses the configuration of B/S all , need to install only in Linux server on , and safety is high. The so server option of operating system is many, no matter choosing those operating system, can let the most of ones use windows in order to the computer of top of a table of operating system does not get influence, this for make most popular free Linux operating system develop fast, Linux except operatingsystem is free besides, it is also free to link database, this kind of option is very pupular.Say, many persons on daily, "Sina website" nets , so long as having installed browser for can , and what need not know the server of " Sina website " to use is that what operating system, and in fact the most of websites do not use windows operating system really, but the computer of user is most of as installing to be windows operating system.( 3 ) Application server operation data load value comparatively.Since B/S configures management, software installation in server end ( Server ) on, it is been all right that network administrator need to manage server only, the user interface major logic of general affairs in server ( Server ) end pass through WWW browser completely realization, lose the logic of general affairs very much in front( Browser) realization, all customer ends has only browser, network administrator need to do hardware maintenance only. But application server operation data load is heavier, once occuring " server collapse " to wait for problem, consequence is unimaginable. Therefore a lot of units have database to stock server , are ready for any eventuality.原文翻译:利用ASP开发Web应用程序首先必须确立Web应用的体系结构。
计算机外文文献
计算机外文文献外文文献Computer network virus and precautionsWith the new network technology and application of the continuous rapid development of the computer network should Use of becoming increasingly widespread, the role played by the increasingly important computer networks and human More inseparable from the lives of the community's reliance on them will keep growing. With the continuous development of computer technology, the virus has become increasingly complex and senior, the new generation of computer viruses make full use of certain commonly used operating systems and application software for protection of the weak low spots have rampant in recent years as the popularity of the Internet in the world, will be attached document containing the virus the situation in the mail has been increasingspread of the virus through the Internet, making the spread of the virus speed Sharp also increased, by an ever-increasing scope of the infection. Therefore, the protection of the security of computer networks will become increasingly important.First,a computer virusA computer virus the definition of computer virus computer virus (Computer Virus) in the "people's republic of China the computer information system security protection regulations "which has beenclearly defined, the virus" refers to the preparation or computerprogram inserted in the damage or destruction of computer data functions, affecting computer use Self-replication and can a group of computer instructions, or code. "Second, network virusWith the development of network and the Internet, a wider spread,the greater New harm the virus emerged this is the Internet virus. The virus is an emerging concept in the traditional the virus was not classified network virus this concept, because the development of networks, the traditional virus the network also has a number of characteristics. Today's Internet virus is a broad notion of as a longas it is carried out using the Internet to spread destruction can be known as network viruses, such as: "Love the back door", "Panda burning incense."Third, network virus and the distinction between computer virusThe original common computer virus is nothing more than the devastating formatted hard drive, delete system with the users documents, databases, etc.destruction. The mode of transmission is through nothing but also by virus infection mutual copy of the software, carrying the virus, such as the use of pirated optical discs, such as infection disk systems the pilot virus and infected executable file virus, in addition to a network virus these are the common characteristics of the virus,but also steal users with remote data, remote control of the other side computers and other damaged properties, such as Trojan and consumptionof funding the operation of the network computer source collapse of the network server worm.Fourth, the network against virusNetwork destructive virus, will directly affect the work of the network, ranging from lowering speed video ring for the efficiency of the network, while in the collapse, undermining the server information to a multi-year work destroyed Dan. Because viruses and other network annually fraud led to economic losses of over 16 billion yuan, But this figure is constantly rising year by year. The next few years, the size of the market will reach Security 60 billion yuan. One antivirus software experts pointed out: "Network avian flu virus even more." Such as: "Xiong Cat burning incense "In addition to virus infection through the web site users, the latest virus also through QQ Loopholes in propagating itself through file-sharing networks, the default sharing, weak password systems, U disk and windows forms bottom of the top mobile hard drives, and other means of communication. While LAN once a computer machine for infection, it can spread through the entire network instant, or even within a very short period of time can be infected thousands of computers, can lead to serious networks. Symptoms of poisoning in the performance of computers there are enforceable. Exe files have become a strange pattern, the pattern shown as "Panda Burning incense, "and then System blue screen, restart the frequent, hard drive data destruction, serious entire company all computer LAN will all poisoning. "Panda burning incense," only more than half a month, a few varieties have highof more than 50, and the number of its users infected constantly expanding. Makes infected, "Panda burn incense" disease the personaldrug users has been as high as several million people infected with afew more corporate users is rising exponentially. Network more on the computer network the greater the harm caused by the virus.Fifth, Network transmission of the virus Features1. Infection fast: single machine environment, the virus can only be passed fromone computer diskette to another, and in the network can be adoptedby the rapid spread of network communication mechanism. According to measurement set against a typical PC network use in normal circumstances, once a computer workstation sick drugs, and will be online within 10 minutes in the several hundreds of all infected computers.2. Proliferation of a wide range: in the network due to the spreadof the virus very quickly and spread to encompass a large area, not only the rapid transmission of all LAN computer, but also through remote workstations virus in moment inter spreadto thousands of miles away.3. Dissemination in the form of complex and varied: computer viruses in general through the network " Station server workstation "channels of communication, but in the form of complex and diverse communication.4. Difficult to completely wipe: the standalone computer viruscarriers sometimes can be deleted documents or low-level formatted drives, and other measures to eliminate the virus completely, and thenetwork once a computer work clean stations failed to disinfect the entire network can be re-infected by the virus, or even just completed removal the work of a workstation is likely to be on-line by another workstation virus infection. Therefore, Only workstations in addition to killing viruses, and can not solve the virus harm to the network is.中文译文计算机网络病毒与防范随着各种新的网络技术的不断应用和迅速发展, 计算机网络的应用范围变得越来越广泛, 所起的作用越来越重要, 计算机网络与人类的生活更加密不可分, 社会对其的依赖程度也会随之不断增长。
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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。
这些设备使用无线电波或红外信号作为一种传输媒介。
ITU-T（电信标准部门）的G.hn技术使用现有的家庭布线（同轴电缆，电话线和电源线）创建一个高速（可达1Gb/S）局域网。
3.2有线技术双绞线是目前应用最广泛的通讯媒介。
它由铜线扭曲配对而成。
普通电话线由两个绝缘铜导线配对扭成。
计算机网络布线由四对铜电缆构成，可以进行语音结构和数据传输。
使用双绞线电缆可以减少交调失真，电磁感应。
它的传输速度的范围很广，从200万b/s至1亿b/s。
双绞线电缆有两种类型非屏蔽双绞线(UTP)和屏蔽双绞线(STP)，它们被用在不同的场合。
同轴电缆广泛用于有线电视系统、写字楼、和其他工作区域的局域网。
该电缆通常由铜或铝合金丝用带有高介电常数的灵活性材料绝的缘层包裹，所有这一切都被导电层环绕。
绝缘层帮助减少干扰和变形。
传播速度的范围从2亿b/s到超过5亿多b/ s。
光纤，是由一个或多个细丝状的玻璃纤维包裹在保护层中。
光纤不受电磁辐射。
它透过光线延续的传播速度可以达到上万亿b/s。
光纤的传输速度比同轴电缆的传输速度快几百倍，比双绞线的速度快上千倍。
3.3无线技术地面微波——使用地面上的微波发射器和接收器。
设备看起来像卫星接受器。
地面微波使用的是频率在千兆赫范围以内的波，这限制了所有通信线路出现在我们的视线中。
中继站之间的距离大约为30英里。
微波天线通常放在建筑物的顶上，例如：塔、丘陵或者山峰的峰顶。
通信卫星——卫星广播使用微波通信，而微波传输不会因地球大气层而产生偏转。
卫星安置在太空中，一般在赤道上22000英里(对于同步卫星来说)的高空。
这些绕地卫星系统能接收和转播语音、数据、电视信号。
蜂窝技术和个人通信服务系统，使用几种无线电通讯技术。
这类系统被分布到不同的地理区域。
每个区域都有低功率发射器或无线电中继天线装置来把电话通信从一个地区传递到下一个地区。
无线LAN,即无线局域网使用高频无线电技术，类似数字蜂窝和低频无线电技术。
无线局域网使用扩频技术来实现有限区域内多个设备之间的通信。
一个开放式标准的无线电波技术的例子就是IEEE。
红外通信，它能在设备之间进行短距离的不超过10米的点对点(面对面)的信号传输，传输线路之间不能有障碍。
3.4规模网络通常分为局域网(LAN)、广域网(WAN)、城域网(MAN)、个人区域网络(PAN)、虚拟专用网(VPN)、校园局域网(CAN)、存储区域网络(SAN)。
而其它一些国家，则根据其规模、范围和目的分类。
例如，控制器局域网(CAN)的使用，信任水平和进入权利之间同这些类型的网络大有不同。
局域网往往是专为内部使用的一种组织内部系统和员工个人物理位置的网络，比如建筑，而广域网路可以连接物理上独立的部分，而且可能包括连接一个组织给第三方。
3.5功能关系(网络体系结构)计算机网络的功能关系可以根据元素中存在的网络进行分类。
如，主动网络、客户端—服务器、无线自组网络和点对点(工作组)建筑。
3.6网络拓扑结构计算机网络分类是根据网络拓扑结构建立的，如总线网络，星型网络，环网，网格。
网络拓扑的协调基于他们在网络设备上逻辑关系的排列，彼此独立于物理的安排。
即使网络计算机放置在一个线性安排和被连接到一个集线器，网络仍是星型拓朴结构，而不是总线网的结构。
一个网络在这方面的视觉和操作特性是不同的。
网络可以基于数据分类的方法以用于传递数据，包括数字和模拟网络。
4.基于物理范围的各种类型的网络常见的可以确定其规模的计算机网络类型。
4.1局域网局域网(LAN)是一个连接在有限地区的电脑网络或设备。
如家庭、学校、计算机实验室、办公楼、或接近的建筑物。
每台计算机或设备，对网络是一个节点。
新的标准ITU-T G.hn也提供一种方法即使用现有的家庭电线（同轴电缆，电话线和电源线）来创建一个有线局域网。
典型的图书馆网络，在一个分支树拓扑结构和控制对资源的访问所有相互关联的设备必须了解网络层(第三层)，因为他们要处理多个子网(不同的颜色)的。
图书馆里面只有10/100 Mbit / s的以太网连接到用户设备和千兆以太网连接到中央路由器，可以称为―第3层交换机‖，因为他们只有从以太网接口才能了解IP。
这将是更正确的称呼他们的接入路由器，在顶部的路由器是一个通讯路由器，它是学生连接到互联网和学院网络的接入路由器。
局域网的界定特征，和广域网络(广域网的关系)相比较而言，局域网有更高的数据转移率、小地理范围,并且不需要租赁电信线路。
当前的局域网或其他电气与电子工程协会802.3局域网技术操作的速度达10 千兆比特/秒。
这是数据传输速率。
IEEE已经计划审查的标准是40到100 千兆比特/秒。
4.1.1个人区域网个人区域网络(盘)是用于一个人周围的计算机和使用不同信息技术的设备之间进行交流的网络。
在个人区域网中使用的设备有个人电脑、打印机、传真机、电话、PDA、扫描仪甚至是视频游戏机。
一个个人区域网可能包括有线和无线设备。
个人区域网的范围通常延伸到10米。
个人有线区域网通常采用USB数据线及高速的序列文件连接来构建,而蓝牙通信技术与红外通信技术则形成了典型的个人无线区域网。
4.1.2家庭区域网络一个家庭区域网络(HAN)是一个住宅局域网，一般可用于部署在家里的数字设备之间的通信，如少量的个人电脑及配件，打印机和移动计算设备。
它的一种重要功能是是通过有线电视或数字用户线（DSL）提供的宽带服务来共享上网，它也可以被称为一个办公区域网络(OAN)。
4.2广域网广域网(WAN)是覆盖了一个城市，国家一个很大地理区域的计算机网络,如城市、国家或跨洲际距离,使用的通信信道是有多种媒体如电话线、电缆和无线电波相结合的信道。
广域网使用的传输设备通常是有公共电信运营商提供的，如电话公司。
广域网技术的一般功能体现在开放式系统互连（OSI）参考模型较低的三层:物理层,数据链路层和网络层。
4.2.1校园网校园网是一个在有限的地理区域连接成的局域网(LAN)计算机网络。
网络设备(交换机、路由器)和传输媒体(光纤、铜厂、Cat5布线等)是几乎完全属于(校园承租人/所有者的:企业、学校、政府等)。
就大学校园的校园网络建设来说，网络是将各种各样的校园建筑，如，学术部门，大学图书馆和学生学员公寓等连在一起的。
4.3城域网一个大城市的网络是一个大型计算机网络，通常跨越城市或一个大的校园EPN帧中继广域网的连接和远程拨号访问。
VPN用来连接3个办公室和远程用户4.3.1企业专用网企业网是由企业建设用来互联公司各个部门的网络，如生产基地、总部、远程办公室、商店等为了共享电脑资源而设立的。
4.3.2虚拟专用网虚拟专用网络（VPN）是一种特殊的计算机网络，其中某些节点之间的联系通过公开式电路连接或通过一些较大的网络（例如，互联网）中的虚拟链路，而不是通过物理线路。
这种通过大型网络的虚拟专用网使用的数据链路层协议被称为隧道。
安全通信是公用因特网中一个常见的应用，但VPN不需要这种明确的安全性能，如认证或者内容加密。
例如，VPN可以被用来分离不同用户在拥有强大安全特性的底层网络进行通讯时的流量。
VPN可能有尽力而为的特性或在VPN客户端和VPN服务提供者之间有固定的服务等级协定(SLA)。
一般来说，VPN拓扑比点对点要复杂的多。
4.3.3互联网络一个网际网路使用路由器通过一种常见的路由技术(OSI第三层) 连接两个或更多的私人计算机。
互联网是许多互联网络的一个集合，因此被缩短称为互联网。
4.4骨干网骨干网络(BBN)，骨干网络或网络骨干是计算机网络基础设施的一部分，它连接了不同种类的网络，并且它提供了不同局域网和不同子网之间进行通信的路径。
骨干网可以将在同一座楼里、不同的建筑物中、校园环境中或国外的不同网络连接起来。
通常，骨干网络的承载能力大于连接到它上面的网络。
在一家拥有分布在不同区域子公司的大公司里，可能有骨干网将不同的区域连接在一起，例如，如果一个服务器集群系统需要被公司内坐落于各种不同的地理位置的部门访问。
将不同部门连接在一起的那部分网络(例如:局域网，无线网)经常被称作网络骨干。
在骨干网络的设计中经常会考虑到网络拥塞的问题。
不应将骨干网络和因特网骨干混同。
4.4.1全球区域网络全球区域网络(GAN)是一个用于支持通过任意数量的无线局域网、卫星覆盖区域等进行移动通信的网络。
移动通信的主要挑战是处理从一个覆盖地区转到另一个地区的用户通信。
电气与电子工程协会802项目涉及一系列地面无线局域网。
4.4.2互联网互联网是一个全球性的联结政府、学术、公司、公共领域和私人计算机系统的网络。
它基于互联网的网络技术协议组件。
这继承了由美国国防部开发研制的高等研究计划署网络(阿帕网)。
互联网也是万维网(WWW)的通信主干。
4.4.3内部网和外部网内部网和外部网是一个计算机网络的延伸部分，它通常是一个局域网。