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

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。

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。

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。

毕业设计外文文献翻译专业交通运输姓名张有节同组成员赖思琪杨鹏指导老师刘习华Campus Network planning and Construction At present, China's rapid development of the cause of the campus network, to early 2003, almost all colleges have set up their own campus network, and carry out a variety of its services and applications. Campus Network build a rich learning resources to enhance the efficiency of education. But as the number of users increased dramatically increased and the pattern of operations, campus network security is increasingly conspicuous, and the ever threat to the healthy development of the campus network, as an education development of the information industry should not be neglected problem. This paper focuses on the campus network design and the process of building the campus network established the goal of building, campus network technology programme design, information resources construction, application software development, network management and security, the five key issues. The campus network is the infrastructure of importance of school, taking the school teaching, research, managing and outward communicate many roles of etc..The safe condition of the campus net affects the teaching activity of the school directly.Set up in the network of initial stage, the safe problem may still be not outstanding, but along with applied thorough, various data of the campus net would nasty play increment, the safe problem beginning of various each kind perplexes us.The Internet flies to develop soon, to the campus network the teachers and the students' life and studies have already produced the profound influence, the network have already not have no place in our life at. But at enjoy the convenience that high technology bring at the same time, we need to be awake of know, the safe problem of network also become the network application more and more increasingly and seriously huge bar, the situation that the campus network safety hazes already arrived and must unify the management and resolve thoroughly, only good resolve the safe problem of network, the application of the campus network then can be healthy, high speed of development. We should consider the comprehensive usage fire wall and encrypt several measures, such as technique and the anti-virus software...etc. completely, work in coordination, strengthening the management, looking for thebalance point of insure the network safety and the network efficiency from it, the safety of the comprehensive exaltation campus network, thus build up rise a set of real in keeping with safe system of the calculator network of the school.The time today's knowledge-based economy and information technology have the development and popularization of Internet in the world have decided the time the network will become the main tool for information. With the development of computer network technology, network has become an important platform for the exchange of information. Internet-based e-learning with time-sensitive, shared, interactive and many of the characteristics of the individual, so it has a traditional teaching model of unmatched advantages. It created a new teaching model, breaking the traditional teaching model at the time and space limitations, the use of advanced teaching methods and teaching methods, greatly improve the teaching efficiency and teaching effectiveness, teaching and learning activities to enable a new level. Do a good job in the design of the campus network, are among the schools, both internal and external communication between the key and convenient.21st century the size of the campus network and application level are reflected in schools and science teaching and learning environment an important component of the force, so we should make use of existing campus conditions, design a secure, unified campus network.Large Campus Network DesignBusinesses operating large campus networks are increasingly looking for infrastructure upgrades to:(1) Handle high bandwidth applications such as voice, video, and IP multicast Improve backbone capacity for shared Ethernet or FDDI campus backbones(2) Support applications based on Novell IPX, DECNET, AppleTalk, and SNA(3) Offer high availability, performance, & manageability for your company's intranet.Use Layer 2, Layer 3, or ATM backbone solutions to expand your large campus network. In typical designs, the buildings or different parts of the campus connect together across a high performance, switched backbone. Network redundancy andhigh availability is provided at each layer. A high capacity, centralized server farm provides resources to the campus, and when combined with Cisco IOS, network management strategies support QoS, security, troubleshooting, and other common management features from end to end.Medium Campus Network Design A medium campus consists of one large building or several buildings. Networking for a medium campus is designed for high availability, performance, and manageability. This is also called a 'collapsed backbone' design for medium campus networks. Additional requirements of these designs typically include:(1) High performance and availability for bandwidth applications such as voice, video, and IP multicast(2) Shared Ethernet or FDDI building backbone which is running out of capacity(3)Support for applications based on Novell IPX, DECNET, AppleTalk, and SNA Based on the Cisco A VVID architecture, these intelligent network platforms and products provide the basis for a complete network solution.Small campus networks DesignIn most cases, network redundancy is not the top priority, but cost effectiveness is. Additional requirements of these designs typically include:(1) High performance and availability for bandwidth applications such as voice, video, and IP multicast(2) Shared Ethernet or FDDI building backbone which is running out of capacity(3) Support for applications based on Novell IPX, DECNET, AppleTalk, and SNA校园网的规划与构建目前，我国校园网事业飞速发展，至2003年初，几乎所有的大中专院校都建立了自己的校园网，并在其上开展了多种服务和应用。

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。

外文文献翻译（2012届）学生姓名学号********专业班级计算机科学与技术08-5班指导教师微软Visual Studio1微软Visual StudioVisual Studio 是微软公司推出的开发环境，Visual Studio可以用来创建Windows平台下的Windows应用程序和网络应用程序，也可以用来创建网络服务、智能设备应用程序和Office 插件。

Visual Studio是一个来自微软的集成开发环境IDE（inteqrated development environment），它可以用来开发由微软视窗，视窗手机，Windows CE、.NET框架、.NET精简框架和微软的Silverlight支持的控制台和图形用户界面的应用程序以及Windows窗体应用程序，网站，Web应用程序和网络服务中的本地代码连同托管代码。

Visual Studio包含一个由智能感知和代码重构支持的代码编辑器。

集成的调试工作既作为一个源代码级调试器又可以作为一台机器级调试器。

其他内置工具包括一个窗体设计的GUI应用程序，网页设计师，类设计师，数据库架构设计师。

它有几乎各个层面的插件增强功能，包括增加对支持源代码控制系统（如Subversion和Visual SourceSafe）并添加新的工具集设计和可视化编辑器，如特定于域的语言或用于其他方面的软件开发生命周期的工具（例如Team Foundation Server的客户端：团队资源管理器）。

Visual Studio支持不同的编程语言的服务方式的语言，它允许代码编辑器和调试器（在不同程度上）支持几乎所有的编程语言，提供了一个语言特定服务的存在。

内置的语言中包括C/C + +中（通过Visual C++）,（通过Visual ），C＃中（通过Visual C＃）和F＃（作为Visual Studio 2010），为支持其他语言，如M,Python,和Ruby等，可通过安装单独的语言服务。

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。

Abstract- With the rapid development of computer network technology, the security of computer network becomes increasingly important. Three main threats facing computer network security include: hackers, computer virus and denial of service attack. Things leading to the safety of the network are mainly: resources sharing, data communication, computer virus and TCP/IP protocol security flaws. A safety network system should include at least three kinds of measures: legal measures, technical measures and review and management measures. The paper analyzes the main threat facing computer network security, discusses network security technology and advances some effective countermeasures in view of the hidden danger of current common network security.Keywords-network security; computer network; information security; security strategy; prevention strategyI.INTRODUCTIONWith the development of Internet technology, computer network gradually changes people's life and way of work. In the process of rapid popularization of computer network, hidden dangers of computer security become increasingly prominent. This requires us take strong measures to ensure the safety of the network. The computer network security refers to the use of network management to control and technical measures to ensure data privacy in a network environment. But as computer network is open, sharing and international, it makes computer network more vulnerable. In order to solve this problem, now people mainly research in the field of data encryption technology, identity authentication, firewall, network management and thatII.CONCEPT OF COMPUTER NETWORK SECURITYThe computer network security refers to the use of network management to control and technical measures to ensure that in a network environment, the data privacy, integrity and availability can be protected. The computer network security includes two aspects: physical security and logic security. The physical security system means that equipment and related facilities are protected from destruction, loss, etc. Logic security includes the integrity of information, secrecy and availability. The meaning of computer network security varies from users to users. Different users have different understanding of network safety requirements. To general users who may just wantindividual privacy or confidential information on the network transmission to be protected and to avoid being eavesdropping, tampering and forge. But for network providers, they not only care about the network information safety, but also consider how to cope with sudden natural disasters, such as a military strike to network hardware damage, as well as how to restore network communication and maintain the continuity of network communication in abnormal situations.Essentially, network security include hardware that compose network system, software and its transfer over a network information safety, which protected it from accidental or malicious attack, network security concerns both technical problems and management issues, which are in complement with each other.III.MAJOR THREATS OF COMPUTER NETWORKA.Internal interception and DestructionThe people inside of network system may become the following possible threats: internal confidential personnel's intentionally or unintentionally leaks, the change of the record information; internal unauthorized personnel's intentionally or not, stealing confidential information, change the network configuration and record information; network system damage from Internal personnel.B.Unauthorized AccessUnauthorized access refers to the unauthorized use of network resources or unauthorized ways to use the network resources. It includes illegal users' hacking into the network or illegal operation system, and legitimate users' unauthorized way of operation.C.Damage the Integrity of InformationAttackers may damage the information integrity from three aspects: changing the order of the information flow, timing, changing the content, the form of information; Deleting news or some of the news; and Inserting some information in the news, making the receiver not able to read or receive the wrong information[2].D.InterceptionThrough the wiretapping or the electromagnetic wave radiation within the scope of the installation, the attacker may intercept confidential information, or through to the information flow, communication frequency and length of6452012 International Conference on Computer Science and Information Processing (CSIP)the parameters find out useful information. It does not damage the transfer information, and it is not easy examinable.E.PretendingThe attacker may pretend to do the following: pretend to be leadership issue orders and read the documents; Pretend to be host deceive legitimate hosts and legitimate users. Pretend to be network control program to show or modify the access to key information, passwords, etc, excessive use of network equipment and resources: take over a legitimate user, cheat the system, take up the resources of the legitimate users.F.Destroy System Availability.The attacker may damage from the following aspects of network system availability: making a legitimate user not able to have normal access to the network resources; Making a strict time required service not able to get the timely response and destroy system.G. Repeat ItselfRepeat itself refers that the attacker intercepted and record information, and then send these information repeatedly when necessary.H.DenialPossible denials are the sender's later denial of sending a piece of news content; the receiver later denied that he had received a message earlier.1.Other ThreatsThe threats of network system also include computer virus, electromagnetic leakage, all kinds of disasters, and the operating error, etc.IV. PROTECTIVE MEASURES OF COMPUTER NETWORK A.Technical Level CountermeasuresFrom technical level computer network security technology mainly include real-time scanning technology, real-time monitoring technology, firewall, completeness inspection protection technology, virus situation analysis report technology and system security management technology. The technical level can take the following measures:1) Establish a system of safety managementImprove the quality of stuff including system administrators and technical personnel professional and users. To the important department and information, strictly inspect virus in computer boot, backup data in time, which is a simple and effective method.2) Network access controlAccess control is the main strategy of network security and protection. Its main task is to guarantee that the network resources are protected from illegal use and access. It is one of the most important strategies of network security. The technology of access control involves many things such asnetwork access control, directory level control and attributes control[3].3) Database backup and recovery.Database backup and recovery is the important operation of database administrators to maintain data security and integrity. Restore database backup is the easiest and can prevent most accident. Recovery refers to the operation of using backup to restore data after accident. There are three main backup strategies: only backing up the database, backing up the database and affairs log and incremental backup.4) Application code technologyApplication code technology is the core technology of information security. Information security password is to provide a reliable guarantee. Based on code of digital signatures and identity authentication to guarantee that the main method of information integrity, one of which include classical code techniques, single key code system, public key code system, digital signature and key management.5) Cuting off the transmission wayCarry on a thorough antivirus examination on affected hard disk and the computer, don't use the unexplained USB disk and the program, don't download SUSpICIOUS information.6) Improve anti-virus technology of networkBy installing virus firewall, real-time filtering IS conducted. The files server on the network should be frequently scanned and monitored, using anti-virus software in the work site, strengthening the network directory and file access settings[4].7) Conduct research and development to improvethe operation of the high quality security system.Research and develop high security operating system, and don't give the virus hotbed to live, which would make computer network safer.B.Management Level CountermeasuresThe computer network security management not only depends on the security technology and preventive measures, but also depends on the management measures it takes and the protection laws and regulations it implements. Only by linking them closely can we make the computer network security really effective.The computer network security management includes educating users of computer safety, and setting up corresponding security management institution, continuous improvement and strengthening the management function, strengthen works on computer and network of the legislation and law enforcement, etc. Strengthen computer security management and enhance the user of the laws, regulations and moral concepts, improve computer users' awareness of safety, to prevent the computer crime and resistance to the hacker attacks and prevent computer virus interference, are all very important measures.This means the ongoing legal education on computer users, including computer security law, code, data and so on, make the right and obligation clearly to computer users and systems management personnel, consciously abide by the legal information system principle, legal principle, the6462012 International Conference on Computer Science and Information Processing (CSIP)principle of public information, information use principle and resource constraints principle. Consciously fight against all the behavior of the illegal crime, maintain the safety of the computer and network system, and the safety of the information system. In addition, we still should educate computer users and the staff, and obey all the rules and regulations set up for maintenance system safety, including personnel management system, operation maintenance and management system, computer processing control and management system, all kinds of material management system, computer room management system, special plane to defend the special division of work and strict management system.C.Physical Security Level CountermeasuresTo ensure the safety of computer network system's reliability we must ensure that there is a security system entity of the physical environment conditions. The safe environment refers to computer room and its facilities, mainly include the following content:1) Computer system environment conditionsThe computer system security environment conditions include temperature, humidity, air cleanliness, corrosion degrees, insect, vibration and impact, electrical disturbance and so on, which all have specific requirement and strict standards.2)Computer room environment selection control to identifY users' identity, and to verifY its validity; Secondly, visitors must define the scope of activities; Thirdly, multilayer safe protection should be set in the center of computer system to prevent illegal invasion of violence; Fourthly, buildings where equipment is located shall have equipment to protect against all kinds of natural disasters.V.CONCLUSIONThe computer network security is a complicated system of engineering, involving technology, equipment, management, system and so on, and security solutions should be set and understood from the whole. Network security solution is a combination of various security technologies in computer network information system, one that combines safe operating system technology, firewall technology, virus protection technology, intrusion detection technology, and security scanning technology, which forms a complete set of network safety protection system. We must make sure that management and technology, safety technology be integrated with safety measures, and strengthen the computer legislation and enforcement of law, establish backup and recovery mechanism, make corresponding safety standards, and strengthen the network security management measures. Only in this way can we ensure the security of the computer network.REFERENCESThe choosing of a suitable installation place for computer system is very important which directly affect the reliability and safety of the system. When choosing a computer room, we should pay attention to its external environment safety, reliability, avoid strong vibration sources and strong noise source, and avoid high buildings and water in the lower equipment or the next door. The management of the entrance should also be noted[5].3) Computer room safety protectionThe computer room security protection is designed for the physical environment and to prevent disaster from unauthorized individuals or group damage, tampering or theft of network facilities, important data and take security measures and countermeasures. In order to manage regional security, first of all, we should consider the physical access摘要——随着计算机网络技术的快速发展,计算机网络的安全变得越来越重要。

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。

PROCESS DESIGN AND CONTROLComputer-Aided Simulation Model for Natural Gas PipelineNetwork System OperationsPanote Nimmanonda,Varanon Uraikul,Christine W.Chan,andPaitoon Tontiwachwuthikul*Faculty of Engineering,University of Regina,Regina,Saskatchewan,Canada S4S0A2This paper presents the development of a computer-aided simulation model for natural gaspipeline network system operations.The simulation model is a useful tool for simulating andanalyzing the behavior of natural gas pipeline systems under different operating conditions.Historical data and knowledge of natural gas pipeline system operations are crucial informationused in formulating the simulation model.This model incorporates the natural gas properties,energy balance,and mass balance that lay the foundation of knowledge for natural gas pipelinenetwork systems.The user can employ the simulation model to create a natural gas pipelinenetwork system,selecting the components of natural gas,pipe diameters,and compressorcapacities for different seasons.Because the natural gas consumption rate continuously varieswith time,the dynamic simulation model was built to display state variables of the natural gaspipeline system and to provide guidance to the users on how to operate the system properly.The simulation model was implemented on Flash(Macromedia)and supports use of thesimulation model on the Internet.The model was tested and validated using the data from theSt.Louis East system,which is a subsystem of the natural gas pipeline network system ofSaskEnergy/Transgas Company.The model can efficiently simulate behaviors of the pipelinesystem with satisfactory validated results.1.IntroductionNatural gas is one of the most widely used sources of energy in North America,especially in Canada.Efficient operations of natural gas pipelines are important for ensuring gas transmission to customers.Construction of a natural gas pipeline network system can be difficult because of variations in customer consumption rates, which directly influence system properties such as the inline pressure and the volume of natural gas transmit-ted.These parameters also vary depending on the season.To better support the design of natural gas pipelines,constructing a model that can simulate the operational behaviors of the system is important.To construct a simulation model,historical and current observations collected on system behaviors are needed. Simulation models can provide predicted system behav-iors based on a number of“what if”scenarios about the real-world system.Some relevant works that describe the use of simulation models in industrial processes include the following:Simulations have been applied to different disciplines,including engineering,social science,and business by Banks.2A simulation model for the control of food freezing processes using a discrete dynamic technique with quantitative knowledge was proposed by Banoune and Depeyre.3A basic steady-state and dynamic simulation model in which every plant component was represented according to a graphical modeling technique was applied to a power plant system by Lu.10The main objective of this paper is to present the development of a computer-aided simulation model for natural gas pipeline network systems.Such a system can assist users in the design of a natural gas pipeline network system.The simulation model was designed to support the following tasks:(1)specifying the key components of a generic natural gas pipeline network system,(2)providing practical knowledge and a suitable mathematical model for the system,(3)helping users to construct a natural gas pipeline network system that models their real systems on the Internet,and(4) analyzing and predicting the behaviors of systems dynamically under changing conditions of operations. The model was implemented on Flash development software(Macromedia).Flash is an environment for designing and delivering low-bandwidth animations, presentations,and Web sites.It contains powerful multimedia capabilities and also offers scripting capa-bilities and server-side connectivity for creating interac-tive elements and Web applications.This paper is organized as follows:Section2presents an overview of the operations of a general natural gas pipeline network system,including the main compo-nents of the system and their characteristics.This section also explains how the characteristics of system components are formulated into a mathematical model. Section3describes the role of each component in the simulation model,including how the data are processed*To whom correspondence should be addressed.Tel.:(306)585-4160.Fax:(306)585-4855.E-mail:paitoon@uregina.ca.990Ind.Eng.Chem.Res.2004,43,990-100210.1021/ie030268+CCC:$27.50©2004American Chemical SocietyPublished on Web01/09/2004and the results generated.Section4describes a case study and how the graphical user interfaces are used. The data from the case study are integrated with the simulation model for testing.Section5discusses the results of the test,as well as their verification and validation.Finally,the conclusions and agenda for future work are given in section6.2.Natural Gas Pipeline Network SystemA natural gas pipeline system involves a set of operations and components that must be clearly under-stood before a simulation model can be built.2.1.Natural Gas Operations.The tasks of natural gas operations involve monitoring parameters of the pipeline system,determining customer demand for natural gas,and adjusting operations to meet demand. The main task of the dispatcher is to regulate compres-sors to control the pressure of natural gas in the system. Effective operation of the compressor is not easy,as there are many factors to consider and many compo-nents in the pipeline system.2.2.Main Components of Natural Gas Pipeline Network Systems.There are five main components in a natural gas pipeline network system:the natural gas,the pipeline network system,the compressor sta-tions,the customers,and the ambient temperature of gas.Each can affect the condition of the natural gas pipeline system in different ways.(1)Natural gas is mainly utilized for heating in households and industries.It is customarily defined as a mixture of gases,including both hydrocarbons and non-hydrocarbons.All hydrocarbon gases are character-ized by the general formula of C n H2n+2,and the non-hydrocarbon gases are nitrogen and carbon dioxide.The principal component in natural gas is methane(CH4), which does not condense to a liquid under any typical operating conditions.Normally,natural gas in a pipeline system contains85-95%methane,along with varying small proportions of ethane,propane,and butane and a maximum of about5%non-hydrocarbon components.15 If the composition in terms of percentages of the components should change,then the properties of the natural gas are also altered.(2)Pipeline network systems constitute an economical means of transporting fluid over long distances because they have low operating and capital costs,which decline further with larger volumes of throughput.Many factors are involved in the design of long-distance natural gas pipelines,including the type and diameter of pipes and the length of the pipelines.The type of pipe can affect the characteristics of natural gas operations.One of the main concerns is the roughness of the pipe,which directly affects the friction factor of a pipe.The fiction factor increases in proportion to the pipe’s roughness and is used to compute the magnitude of the pressure drop due to friction between the fluid and the surface of the pipe.The length of a pipeline is usually measured from one natural gas station to another,from a natural gas station to a customer area,or from one customer area to another.It is desirable for the pipe length to be minimized in order to reduce capital and operating costs.The diameter of a pipe can affect the volume of natural gas transmitted at a given natural gas velocity because pipes with larger diameters can transmit more natural gas than those with smaller ones.However,a pipe with a larger diameter also has a higher cost. Therefore,pipeline designers or engineers have to consider these factors in optimizing the capital and operating costs.(3)Compressor stations contain compressors for in-creasing,maintaining,and decreasing pressure in the pipeline system.In general,the compressors can gener-ate pressure to satisfy the demand of all customers in the pipeline system.(4)The type of customer is a key factor that affects the flow rate in the pipeline at a given time.Natural gas customers can be categorized into four types,i.e., residential,farming,commercial,and industrial,and each category of customers consumes natural gas at a different rate.For example,the demand of industrial customers is constant,whereas the demand of residen-tial customers fluctuates during different periods of time in a day.Statistically,the maximum consumption occurs in the mornings and evenings because the customers utilize natural gas for cooking and heating in the mornings and for heating houses and buildings in the evenings.(5)Ambient temperature affects customer consump-tion of natural gas;that is,the consumption rate varies depending on the season.In winter,customers consume more natural gas than they do in summer.The con-sumption rate usually hits the highest level in winter and the lowest level in summer.Meanwhile,in fall and spring,the consumption rate is at a moderate level.2.3.Natural Gas Properties.Natural gas properties are the basic considerations that provide the basis for calculating indicators of the state of a pipeline system such as the pressure and flow rate of the natural gas. Five natural gas properties are involved in the simula-tion model:molecular weight,gas gravity,compress-ibility factor,gas density,and viscosity.These properties are described as follows:Molecular Weight.Molecular weight can be deter-mined using eq1where M g is the overall molecular weight of the natural gas,M i is the molecular weight of each hydrocarbon or non-hydrocarbon component i,and y i is the mole fraction of each hydrocarbon or non-hydrocarbon component i. Gas Specific Gravity.In natural gas,specific grav-ity can be defined using eq2whereγg is the gas specific gravity,M g is the natural gas molecular weight,and M a is the air molecular weight.Compressibility Factor.To obtain the compress-ibility factor,the pseudo-reduced temperature(T r)and pressure(p r)must be first calculated using eqs3and 4,respectivelywhere T r is a pseudo-reduced temperature and p r is a pseudo-reduced pressure;T and p are the operating temperature and pressure,respectively;T c and p c are the critical temperature and pressure,respectively. To obtain the value of the critical temperature and pressure of a gas mixture,Key’s mixture rule can be applied to determine the pseudo-critical temperatureMg)∑y i M i(1)γg)Mg/Ma(2)Tr)T/Tc(3)pr)p/pc(4)Ind.Eng.Chem.Res.,Vol.43,No.4,2004991and pressure as followswhere T pc and p pc are the pseudo-critical temperature and pressure,respectively;y i is the mole fraction of each hydrocarbon or non-hydrocarbon component i;T c i and p c i are the critical temperature and pressure,respec-tively,of each component i.Table1provides the values of molecular weight, critical pressure,and critical temperature of the hydro-carbon and non-hydrocarbon components of natural gas.4In practice,a Standing and Katz chart is used to illustrate the relationship between the values of pseudo-reduced temperature T r,pseudo-reduced pressure p r, and compressibility factor Z for sweet natural gas. However,to make the chart applicable for simulation programming,a straight line was introduced to fit the Standing and Katz chart in a general form as5where A-D are correlation constants,Z is the com-pressibility factor,T r is the pseudo-reduced tempera-ture,and p r is the pseudo-reduced pressure.Gas Density.The density of natural gas F g can be calculated aswhere M g is the molecular weight,p is the pressure,R is the gas constant,Z is the gas compressibility factor, and T is the temperature of the system.Viscosity.Two types of viscosity can be used to characterize natural gas behavior:dynamic and kine-matic.The dynamic viscosity,a measure of a fluid’s resistance to flow,is defined as the ratio of the shear force per unit area to the local velocity gradient;this is represented by whereµis the dynamic viscosity,F is the flow rate,A is a unit area,v is the velocity gradient,and L is the length of the pipe.If temperature is involved,the equation for dynamic viscosity can be expressed as8whereµis the dynamic viscosity,M is the molecular weight,F g is the gas density,and T is the temperature of the system.Kinematic viscosity is the ratio of the dynamic viscos-ity of a fluid to its density,i.e.where v is the viscosity,µis the dynamic viscosity,andF is the gas density.2.4.Background on Gas Flow in Pipelines.The mathematical models used to design a natural gas transmission pipeline network system are based on algorithms derived from the principles of thermody-namics and fluid flow.They affect the characteristics of the natural gas flow that include system mass balance,system energy balance,and friction factor. System Mass Balance.The mass flow rate through the control volume does not vary with time.Therefore, the mass flow rate into the control volume must be equivalent to the mass flow rate out.This can be expressed aswhere d m cv is the system mass balance;m cv is the mass flow rate in a control volume;and m in and m out are the mass flow rates entering and leaving the control volume, respectively.System Energy Balance.Weymouth developed a general equation for calculating the steady-state iso-thermal flow of a gas through a horizontal pipe,based on the concept of energy conservationwhere q sc is gas flow rate measured at standard condi-tions in thousands of standard cubic feet per day (Mscfd),p sc is the pressure at standard conditions in pounds per square inch absolute(psia),T sc is the temperature at standard conditions in Rankine,p1is the upstream pressure in psia,p2is the upstream pressure in psia,d is the diameter of the pipe in inches,γg is the gas gravity,T is the flow temperature in Rankine,Z av is the average gas compressibility factor, f is a friction factor,and L is the length of the pipe in feet.Reynolds Number and Friction Factor.The Rey-nolds number can be determined using the velocity, density,and viscosity of the fluid as well as the cross-sectional area of the pipe.6Equation14is used to calculate the Reynolds numberwhere N Re is the Reynolds number,q sc is the gas flowTable1.Physical Constants for Typical Natural Gas Constituentscomponent molecularweight(g/mol)criticalpressure(psia)criticaltemperature(°R)CH416.043667.8343.1C2H630.070707.8549.8 C3H844.097616.3665.7 n-C4H1058.124550.7765.4 i-C4H1058.124529.1734.7 n-C5H1272.151488.6845.4 i-C5H1272.151490.4828.8 n-C6H1486.178436.9913.4 n-C7H16100.205396.8972.5 n-C8H18114.232360.61023.9 n-C9H20128.259332.01070.4 n-C10H22142.286304.01111.8 N228.013493.0227.3 CO244.0101070.9547.6 H2S34.0761306.0672.4 O231.999737.1278.6 H2 2.016188.259.9 H2O18.0153203.61165.1µ)10-4(9.4+0.02M)T1.5209+19M+Texp[(3.5+986T+0.01M)F g1.7+(197.2/T)+0.002M](10)v)µ/F(11)min)moutat d mcv)0(12)qsc)5.6353821(T sc p sc)[(p12-p22)d5γgZavTfL]0.5(13)NRe)20qscγg/(µd)(14)Tpc)∑y i T c i(5)ppc)∑y i p c i(6)Z)pr (ATr+B)+CTr+D(7)Fg)pMg/ZRT(8)µ)F/Ad v/d L(9)992Ind.Eng.Chem.Res.,Vol.43,No.4,2004rate in Mscfd,γg is the gas gravity,µis the dynamic viscosity in centipoise (cp),and d is the diameter of the pipe in inches.For gas flow in a smooth pipe,the friction factor depends mainly on the Reynolds number as followswhere f is a friction factor and N Re is the Reynolds number.Equation 15is applicable for the Reynolds numbers between 3000and 1000000.pressor Characteristics.According to the experience of operators who have long been operating compressors,the compressor capacity can be described as a function of the flow rate and the compression ratio in a graph as shown in Figure 1.Thus,the ratio of the discharge and suction pressures of a compressor can be expressed in the following formulaswhere R is the compression ratio and q is the flow rate in millions of standard cubic feet per day (MMscfd).When the compression ratio R has been defined and one of the values of either the discharge pressure,p discharge ,or the suction pressure,p suction ,is known,then the value can be computed with the following equation2.6Customers’Consumption Characteristics.Three major groups of natural gas consumers must be considered:industrial,dehydrator,and heat-sensitive.17Each group exhibits a different pattern of natural gas consumption expressed as a relationship between time and pressure,as shown in Figure 2.Natural gas is mainly utilized for heating purposes.Hence,the ambient temperature is the main determi-nant in the natural gas consumption of customers.14As a result,the natural gas demand is high in the winter and low in the summer.Figure 3shows a graph of natural gas demand during a typical year from January to December.If the consumption rate of each type of customer within one year is available,the total consumption rate of all customers in each season can be derived from the expressionwhere TotalConsmp is the total consumption rate,%MC is the percentage of consumption compared to the maximum load according to seasons,D is the yearly consumption of residential customers,C is the yearly consumption of commercial customers,F is the yearly consumption of farming customers,I is the yearly consumption of industrial customers,%IC is the per-centage consumption of industrial customers according to seasons,and days is the number of days of consump-tion in the year.2.7.Schematic of Natural Gas Pipeline Network System.The basic features in a natural gas pipeline network include pipes connected to form a pipeline network and natural gas flowing in at one end and out at the other end.A pipeline network generally consists of compressor stations and customer areas.For long-distance delivery,compressor stations need to be located between the primary compressor stations and customer areas to the maintain pressure of the natural gas throughout the pipeline network.Pipelines that branch out from the main lines transmit natural gas to several customer areas,as illustrated in Figure 4.The fundamental components of the natural gas transmission pipeline consist of nodes and node-connecting elements.Nodes are the points where a pipe leg ends,where two or more node-connecting elements are joined,or where there is an injection or delivery of natural gas.Node-connecting elements include pipe legs,compressor stations,valves,and pressure and flow regulators.Figure 4illustrates a loopless pipeline network system for natural gas transmission.A loopless pipeline network system contains nodes joined by one or more node-connecting elements with no closed loops.Such a system usually begins at the compressor station at node 1and transmits natural gas from node 1to node j ,for j )2,3,...,n +1.Between node 1and node 2,there is a pipe leg 1.Therefore,for n +1nodes intotal,Figure 1.Relationship between compressor capacity per unit flow rate and compression ratio.f )0.0056+0.5N Re-0.32(15)R )(0.4/18)[(BHP/q )+44.5]at 5<(BHP/q )<23(16)R )(0.4/12)[(BHP/q )+22.0]at 23<(BHP/q )<35(17)R )(0.1/2)[(BHP/q )+3.0]at 35<(BHP/q )<37(18)R )p discharge /p suction(19)Figure 2.Patterns of natural gasconsumption.Figure 3.General curve of natural gas demand in a year.TotalConsmp )[%MC ×(D /days +C /days +F /days)]+[(I /days)×%IC](20)Ind.Eng.Chem.Res.,Vol.43,No.4,2004993there are n pipe legs.At each node between node 1and node n +1,natural gas is delivered to each customer area.Mass balance and energy balance equations can be used to calculate the pressure and flow rate at each node.If one value among the node pressure,inlet pressure,or outlet pressure is given,the others can be calculated by a given set of pipe leg parameters and the flow rate into or out of the nodes.To determine the pressure at any node,eq 13can be generalized aswhere i )1,2,3,...,n ;j )2,3,...,n ,n +1;and p i is thepressure,q i is the flow rate;and k i is the correlation variable at node i .Meanwhile,the flow rate at a node can be computed using the mass balance equation applied from eq 12.By applying the mass balance equation with an analogy of Kirchhoff’s law for the flow of electricity in electrical networks,the sum of natural gas flows entering and leaving the pipeline system at any node is zerowhere m is the number of node-connecting elements andq i is the flow rate of natural gas at each node i .q i assumes a positive value for flow into node i and a negative value for flow out of node i.3.Conceptual Framework of a Computer-Aided Simulation Model for Natural Gas Pipeline Network SystemsThe components of the natural gas pipeline network and the relationships and properties of these compo-nents form the basis of the simulation model.The correspondence between the components of the pipeline system and the simulation model is shown in Table 2.To simulate a natural gas pipeline network system,the components throughout the system must be clari-fied.From Table 2,the main components,which to-gether make up the system state,consist of the sche-matic of the system,the number of stations,the number of compressors at each station,the customers,the pipes,and the natural gas components.The entities in the simulation model are the compressors,the customers,the pipes,and the natural pressors have their own attributes,such as break horsepower (BHP)and compression ratio.Customers are the entities that determine the natural gas consumption rate of the system.Pipes have attributes of diameter and length.The attributes of the natural gas are the percentages of hydrocarbon and non-hydrocarbon components in the natural gas.The pressure and flow rate at each cus-tomer location,which are the state variables,must be considered.These state variables can be changed by events during operation.The events can be (i)the actions of the dispatcher,such as turning a compressor on or off,or (ii)the change in the entities of the system itself,such as the consumption natural gas.In the actual operating system,the dispatcher moni-tors the state of the natural gas pipeline system from a computer screen.The pressure and flow rate are dis-played and updated within a time interval.The discrete-event simulation approach is applied to build the natural gas pipeline network system because the changes of state variables occur within a time interval.Moreover,the simulation model can dynamically provide the state variables as effectively as a real-time monitoring system does.Figure 5illustrates how the simulation model processes inputs and generates outputs.The simulation model is initialized when the user first inputs the parameters into the simulation model through the user interfaces.The input parameters include a schematic of the system,the number of stations,the number of compressors and the capacity of each com-pressor,number of customers and yearly consumption rate of each type of customer,the diameter and length of the pipes,the percentages of hydrocarbons and non-hydrocarbons componenets in the natural gas,and the range of pressure in the ing these inputs,the simulation model starts to simulate all variables in the natural gas pipeline network system and provide outputs through the user interface.The main user interface illustrates the outputs on the selected sche-matic according to the number of stations,compressors,and customers,as specified by the user.The naturalgasFigure 4.Schematic for the natural gas pipeline network system.p j 2)p 12-∑i )1j -1k i q i 2(21)∑i )1mq i )0(22)Table 2.Correspondence between the Components of the Natural Gas Pipeline Network System and the Items in the Simulation Model simulation model natural gas pipeline network systemsystem stateschematic of the system number of stationsnumber of compressors at each stationnumber of customer areas in the entire network number of pipes in the entire network natural gas componentsentities compressors,customers,pipes,natural gas attributes BHP,compression ratio,consumption rate,pipe diameter,pipe lengthpercentage of each hydrocarbon and non-hydrocarbon component in natural gasstate variables status of compressors (on,off),pressure,flow rateevents turning compressors on/off or up/down,changing consumption rateactivities deliver natural gas994Ind.Eng.Chem.Res.,Vol.43,No.4,2004properties and the state variables,pressure and flow rate,are simulated using all the equations discussed in section 2and displayed on the screen.The natural gas properties,molecular weight,specific gravity,com-pressibility factor,density,and viscosity,can be deter-mined using eqs 1-11.Equations 14and 15are applied to calculate the Reynolds number and friction factor,respectively.According to the season selected by the user,eq 20is used to simulate the consumption rate of customers and represent the flow rate of the pipeline system.To calculate the pressures at the nodes in the pipeline,the energy and mass balance relationships,eqs 21and 22,are applied in the simulation model.The system also generates recommendations on operation control to the dispatchers.Moreover,because of the possible changes in the consumption rates of the cus-tomers,the simulation model is designed to dynamically simulate the consumption rate every 15s.The simula-tion model also allows the dispatcher to decide whether to turn on/off or increase/decrease the capacity of the compressors during operation.When a change in the compressor status occurs,the compression ratio is shifted to a new level,which is calculated using eqs 16-18.Once the consumption rate or actions on compressors are changed,the state variables are automatically updated and displayed on the user interface.4.Case Study of a Natural Gas Pipeline Network System4.1.Background on the Case Study System.The natural gas pipeline network system used as a case study here is located in the St.Louis East area inSaskatchewan,Canada.The system consists of two compressor stations at St.Louis and Melfort.The system spans the region from the St.Louis station to the Melfort station and ends at the Nipawin and Hudson Bay customer areas.Natural gas is transmitted to 32customer areas.Some areas consist of all four types of customers,including domestic,commercial,farming,and industrial.Others have only two or three types of customers.Although there are many customer areas,the dispatcher usually focuses on only the pres-sure at the end points of the pipeline system.The reason for this approach is that,if the pressure at the end points is adequately maintained,the entire pipeline system will have enough pressure.Therefore,the places where the pressure should be gauged are the remote customer areas farthest from the St.Louis and Melfort stations.The most remote customer areas from the St.Louis station before reaching the Melfort station are Melfort and St.Brieux.The most distant areas from the Melfort station are Nipawin and Hudson Bay,located at the end of the pipeline system.Figure 6showsaFigure 5.Diagram of the processes in the simulation model for natural gas pipeline networksystems.Figure 6.Schematic of the St.Louis East system.Ind.Eng.Chem.Res.,Vol.43,No.4,2004995。