计算机网络英语学生论文

A. 英语专业毕业论文

英语专业毕业论文

大学生活在不经意间即将结束，毕业生要通过最后的毕业论文，毕业论文是一种有准备、有计划、比较正规的、比较重要的检验大学学习成果的形式，那么什么样的毕业论文才是好的呢？以下是我帮大家整理的英语专业毕业论文，仅供参考，大家一起来看看吧。

浅析商务英语教学中计算机网络利弊

摘要： 本文通过分析计算机网络在商务英语中的利与弊，探讨计算机网络在商务英语教学中的作用，指出随着信息技术的发展，计算机网络的作用早已远远超出其辅助功能。培养复合型涉外商务英语人才，应打破传统的商务英语教学模式，建立新的以学生为中心的教学模式，强调商务环境下的语言训练。同时，学生不仅要掌握商务英语知识和技能，也要掌握计算机方面的知识和技能。

关键词： 商务英语教学；计算机辅助；教学模式

随着全球经济一体化和我国对外经贸的迅速发展，社会需要越来越多既懂英语，又懂商务的高素质复合型人才。在培养复合型涉外商务英语人才的过程中，商务英语起到了重要作用。通过商务英语教学，一方面，学生可以掌握国际贸易主要术语和必要的商务知识，熟悉经贸业务流程，提高听、说、读、写、译方面的基本能力；另一方面，学生还能掌握商务基本礼仪、经济、贸易等基础理论知识，提高跨文化交际能力，从而最终能够胜任用英语进行对外经贸活动的工作，成为复合型涉外商务英语人才。

一、计算机网络对商务英语教学环境的改善。

商务工作的过程实质上是一种交际过程。商务英语的教学目标是培养在国际商务环境中用英语进行沟通的能力。传统的商务英语教学环境基本上局限在教室和课本上，给学生提供的是零商务环境，导致学生在走上工作岗位时极有可能遭遇“环境休克”，难以将所学知识应用到实际工作中去。

计算机辅助语言学习在我国已经得到重视和应用，并使许多新的教育理念在英语教学中得以实现。

(一)计算机网络能够营造自主学习环境。

Henri Holec提出，学校应该设立两个教学目标：一是帮助学生获得语言和交际能力；二是帮助学生获得自主学习能力。

在商务英语教学过程中，计算机网络使学生能够利用多媒体课件和网络丰富的学习资源进行自学，而不受时间、地点的限制。学生可以根据自身需求和兴趣爱好，自主选择学习内容，调控学习进度，探索学习方法，掌握与商务英语相关的经济、贸易、金融等知识，不断在自身原有经验的基础上建构其对新知识的理解并发展其认知结构。

除了丰富的商务知识外，计算机网络还为学生提供了大量的语言资料，使学生可以不必依赖教师和教材。

各种媒体资源及专门的商务英语教学网站为学生提供了丰富的资源，学生可以自主选择阅读或通过原声电影、英文歌曲、英文广播等多种手段，提高商务英语的听、说、读、写、译基本能力。

以计算机网络为媒介，学生还可以通过电子邮件( e- mail) 、聊天室( chatroom) ，或者MOO (multiuser domainobject oriented)进行一人对一人、一人对多人，或多人对多人的共时( synchronous) ，或非共时交流( asynchronous) ，解决自主学习时遇到的困难。

(二)多信息通道的配合使用有利于改善信息的识记效果。

乔姆斯基(Avram Noam Chomsky)曾指出：“我们大概应该努力为正常人本身拥有的本能的直观判断能力创造一个丰富的语言环境。”人类自然接受信息是通过人的各种感官来进行的，其中包括视觉、听觉、触觉、嗅觉和味觉等，其中视觉和听觉起着最重要的作用。

多媒体技术在商务英语教学中，可以提供丰富的画面、视频、影像和文字，使学生在学习过程中视听结合，图像和声音信息同步输入，有效刺激大脑皮层，提高记忆能力，从而比传统的、单一的以语言为主的教学方式达到更好的教学效果。

(三)大量真实的商务英语材料使语言输入有足够的“重复率”。

Van Patten在谈到语言吸收时认为：“能够被吸收的语言知识在语言输入中必须有足够的‘重复率’( frequen2cy) 和‘凸显性’( salience) ”。计算机、网络和商务英语教学的有机结合，将商务活动方方面面的情景真实地展现在学生面前。学生不仅可以通过计算机、网络找到关于接待、谈判、会议、询盘、发盘、装运、保险等各种商务活动的文字材料，也可以找到相关的听力、视频、音像资料。

就商务活动的某一主题而言，比如询盘，学生可以在网上找到多种对话资料、听力资料、阅读资料、写作资料及文化背景资料。多种资料中商务术语、商务知识的重复出现，使学生潜移默化地提高了语言运用能力，扩大了自己的知识层面。另外，通过计算机网络，教师可指导学生通过网上实时进行国际贸易业务实训，或通过教学软件进行贸易流程的训练。这种真实的商务英语材料不受课本知识的局限，能够激发学生的学习兴趣和热情，将学生的理论知识和真实的商务环境连接起来，帮助学生有效地克服“环境休克”现象。

二、商务英语教学中计算机网络应用的'误区。

与传统的商务英语教学相比，计算机网络的应用使商务英语教学朝着个性化学习和自主式学习的方向发展。

但是，在许多高校的商务英语教学课堂上，教学的本质并未发生改变，还是一种传统的以教师为中心的教学模式。

与传统的黑板+粉笔+录音机的教学形式相比，只是多了光盘、计算机和网络，商务英语课堂教学仍是教师讲、学生听的局面。以商务英语教学中的课文讲解为例，一方面，教师过度依赖课件。教师往往将课本内容完全照搬到多媒体课件中，然后借助课件进行讲解。即使学生课后上网学习和网络版的内容也基本是课本内容的重复，意义不大。在这种情况下，要激发学生的学习潜能，促进学生自主化学习和突出学生的个性化学习之中，就显得非常困难。另一方面，计算机其及网络自身客观上存在局限性，多媒体教学固然生动，但是教师往往在教学过程中给学生提供过大的信息量，而忽视了学生的个体差异。学生在短时间内获得大量的教学信息，在一定程度上抑制了学生的想象力，不利于其解决问题、分析问题能力的发展。

由此可见，在许多高校的商务英语课堂上，普遍认为计算机作为辅助工具用于教学的目的是要帮助教师提高教学手段，其特点是：第一，辅助教师的演示工具(辅助教授难点或重点) ；第二，教学内容基于课本；第三，学生是被灌输知识的对象；第四，不改变教学内容和教学结构；第五，以教师为中心的教学结构。教学上使用的计算机被认为能够增强教师所传授的信息，因为信息被放大在屏幕上。因此，计算机作为一种技术只能起到增强教学效果的辅助作用，而不能真正成为人们用以解决实际问题的工具(Morrison and Lowther， 2005) 。

当今时代，随着信息技术的发展，计算机网络的作用早已远远超出其辅助功能。尤其是在商务领域，人和计算机已经成为一个整体，不能分离。商务活动中，许多具体业务都必须通过计算机及其网络来完成。比如，在电子商务( e - business)中，询盘、发盘、谈判、签订合同等都需要通过电子邮件( e - mail) 、网络聊天等方式来完成。

如果单把计算机网络看做是辅助的工具，是远远不够的。

因为计算机辅助大大削弱了计算机网络本身的功能和作用，不能够从根本上帮助培养复合型涉外商务英语人才，因此需要打破传统的商务英语教学模式，建立新的以学生为中心的教学模式，使学生的知识来源可以扩大到教育网站、数据库、电子书、音像制品、学习课件、报刊杂志、电视广播、教科书、虚拟图书馆、学习软件、网络交流平台及其它材料，教师不再是课堂上的“知识灌输者”，学生变成知识的主动构建者。同时，学生也要在学习商务英语知识、技能的同时，掌握计算机方面的知识和技能。

参考文献：

[ 1 ]陈坚林。 大学英语教学新模式下计算机网络与外语课程的有机整合———对计算机“辅助”外语教学概念的生态学考察[ J ]. 外语电化教学， 2006， (12) : 23.

[ 2 ]黄秀红。 商务英语自主学习环境的构建策略[ J ]. 教育传播与技术， 2006， (2) : 15.

[ 3 ]肖芳菲。 多媒体网络环境下的大学英语教学刍议[ J ]. 琼州大学学报， 2007， (2) : 37.

[ 4 ] Holec H. Autonomy and Foreign Language Learning[M ]. Oxford: Pergamon， 1981.

[ 5 ]Morrison， G. R and Lowther， D. L. Integrating Comput2er Technology into the Classroom [M ]. Pearson EcationAsia L imited， 2005.

B. 计算机网络安全英语论文及翻译求助

Computer network security and to guard against

Abstract: When mankind entered the 21st century information society, the network society of the time, China will establish a complete set of network security system, especially from the policy and law to establish China's own characteristics, network security system.

Key words: computer; network; security; prevent

In the information age, information can help groups or indivials so that they benefit from, the same information can also be used to pose a threat to them, caused damage. Therefore network security, including the composition of network hardware, software and network transmission of information security, so that they do not because of accidental or malicious destruction of the attacks, network security not only the technical aspects, but also management issues, both complement each other, are indispensable.

First, the concept of computer network security
International Organization for Standardization of "computer security" is defined as: "To establish a data processing system and the adoption of technology and management of security protection, the protection of computer hardware, software, data is not e to accidental and malicious destruction of reasons, change and leakage." The above definition of computer security includes physical security and logical security of both the contents of the contents of the logic of security could be understood as we often say that the information security, information refers to the confidentiality, integrity and availability of protection, and network security Information security is the meaning of the extension, that network security is a network of information confidentiality, integrity and availability protection. Computer network security as the specific meaning of the user changes, the user is different on the network security awareness and requirements will be different. From the ordinary user's point of view, could only hope that personal privacy or confidential information transmission on the network be protected against eavesdropping, tampering and forgery; and network provider in addition to care about these network information security, we must also consider how to deal with sudden natural disasters, such as military strikes against the destruction of network hardware, as well as unusual in the network how to restore network communications, and maintain the continuity of network communications.
In essence, the network security, including the composition of network hardware, software and network transmission of information security, so that they do not because of accidental or malicious attacks on the destruction of both the technical aspects of network security issues, there are management issues, the two sides complement each other, are indispensable. Man-made network intrusion and attacks makes network security is facing new challenges.

Second, computer network security status quo
Computer network security is the network hardware, software and data systems are protected from accidental or malicious destruction of reasons, alteration, disclosure, the system continuous, reliable, normal operation of network services without disruption. Computer and network technology has the complexity and diversity, makes computer and network security has become a need to continue to update and improve the area. At present, hackers method has been more than the type of computer virus, and many attacks are fatal. In the Internet network, because the Internet does not have the time and geographical constraints, whenever there is a means to generate new attacks, we can in a week around the world, these attacks means the use of network and system vulnerabilities to attack computer systems and resulting in network paralysis. Worms, backdoor (Back-doors), Rootkits, DOS (DenialofServices) and Sniffer (network monitor) is a familiar means of several hacker attacks. However, none of these attacks means they reflect the astonishing power of today become worse. These types of attacks means the new variant, with previous attacks appeared methods, more intelligent, targeted against Internet-based protocols and operating system level. From the Web process control proceres to the kernel-level Rootlets. Hackers practices escalating renovation, to the user's ability to guard against information security challenge.

Third, computer network security precautions
1, to strengthen the internal network management and the use of safety awareness among staff, many computer systems commonly used passwords to control access to system resources, which is anti-virus process, the most vulnerable and the most economical methods. Network administrator and terminal operator privileges in accordance with their responsibilities, choose a different password for the application data legitimate operation, to prevent unauthorized users to access the data and the use of network resources.
On the network, software installation and management is crucial, it is not only related to network maintenance and management efficiency and quality, but also to the network security. A good antivirus software can be easily installed within minutes to the organization each NT server can also be downloaded and spread to all the purpose of the machine by the network administrator set up and manage to focus, it will work with the operating system and other security is closely linked to become a part of network security management, and automatically provide the best network virus defensive measures. When the computer virus on-line resources applications attack, such as the virus exists in the information-sharing network of media, it is necessary to the security at the gateway, on the network front-end for antivirus.
2, network firewall technology
Is a kind of used to strengthen the network access control to prevent the external network users to illegal means to enter the external network through the internal network, access internal network resources and protect the internal network operating environment special for Network Interconnection Devices. It is between two or more networks such as packet transmission link in accordance with a certain degree of security strategy to implement the inspection, to determine whether the network communication between are allowed to, and monitor the network running. Although the firewall is to protect the network from an effective means of hacking, but there are obviously inadequate: through the firewall can not protect against outside attack other means, can not prevent defectors from the inside and inadvertent threats posed by users, but also can not completely prevent the transmission of the virus have been infected with the software or documents, and can not protect against data-driven attacks.
3, security encryption technology
Encryption technology for the global e-commerce to provide a guarantee, so that Internet-based electronic trading system has become possible, thus improving the symmetric encryption and asymmetric encryption technology is still the mainstream of the 21st century. Symmetric encryption to the conventional password-based technology, computing encryption and decryption operations use the same key. Asymmetric encryption, encryption key that is different from the decryption key, encryption keys are made public, anyone can use, only the decryption key to decrypt people know.
4, the network host operating system security and physical security measures
Network firewall as the first line of defense and can not fully protect the internal network, must be combined with other measures to improve the safety of the system level. After the firewall is based on the network host operating system security and physical security measures. In accordance with the level from low to high, namely, the physical security of the host system, the core operating system security, system security, application services security and file system security; At the same time, host security checks and bug fixes, as well as a backup safety system as a supplementary safety measures. These constitute the entire network system, the second line of defense, the main part of a breakthrough to prevent the firewall as well as attacks from within. System backup is the last line of defense network system, used to attack after the System Restore. The firewall and host security measures is the overall system security by auditing, intrusion detection and response processor constitute the overall safety inspection and response measures. It from the network system firewall, network host or even directly from the network link layer on the extraction of network status information, as input to the intrusion detection subsystem. Intrusion Detection System in accordance with certain rules to determine whether there is any invasion of the incident, if the invasion occurred, the emergency treatment measures, and generate a warning message. Moreover, the system's security audit also can be used as the future consequences of aggressive behavior and to deal with security policy on the system to improve sources of information.
In short, network security is a comprehensive issue, involving technology, management, use and many other aspects, including both its own information system security issues, there are physical and logical technical measures, a kind of technology can only solve the problem on the one hand, rather than a panacea. To this end the establishment of a network with Chinese characteristics, security system, the need for national policies and regulations to support and joint research and development group. Security and anti-security like two sides of contradictions, always pick-up, so the security instry is a future with the development of new technologies and the continuous development of instry.

References:
[1] Huang Yi-qiang, et al. On the software development needs analysis phase of the main tasks. Quarterly Journal of Sun Yat-sen University, 2002 (01).
[2] Hu Daoyuan. Computer LAN [M]. Beijing: Tsinghua University Press, 2001.
[3] Zhu Lisen, even Shougong. Computer Network Application Technology [M]. Beijing: Patent Literature Publishing House, 2001.
[4] Xie Xiren. Computer Networks (4th edition) [M]. Beijing: Publishing House of Electronics Instry, 2003.
[5]孙小刚, Han Dong, et al. Oriented software engineering, Visual C + + Network Programming [M]. Beijing: Tsinghua University Press, 2004,11.

仅供参考，请自借鉴。

希望对您有帮助。

补充：您可以随时找我，我会帮你翻译好发过去，随时欢迎您的咨询。

C. 计算机网络论文的摘要翻译（汉译英）/谢绝用机器翻译，谢谢！

在Internet飞速发展的今天，互联网成为人们快速获取、发布和传递信息的重要渠道，它在人们政治、经济、生活等各个方面发挥着重要的作用。 Today, Internet is developed at full speed, Internet becomes people and obtains, releases and transmits the important channel of information fast, it is playing an important role on such all respects as people's politics, economy, living,etc.. 校园网是利用现代网络技术、多媒体技术及Internet技术等建立起来的学校内部管理和通信应用网络。 Campus network utilizes modern network technology, multimedia technology and Internet technology,etc. Dr.eye: inside the school set up management and communication use the network. 信息化校园就是以校园网和必要的信息服务设备为载体，有丰富的共享软件和方便的工具支持，并包含有相当数量的教育信息资源，集教、学、管理、娱乐为一体的新型信息化的工作、学习、生活的网络环境。 The information-based campus regards campus network and essential information service equipment as carriers, abundant shared software and convenient tool are supported, include a great deal of ecation information resources, network environment of new-type and informationalized work, study and life of incorporating teach, study, the management, amusement into an organic whole.
本设计重点阐述了校园计算机网络系统的设计和实现方法，包括系统设计原则、网络技术选择、综合布线系统、网络拓扑结构及设备选型，本设计可以实现各个模块的基本功能，满足校园内部各部门的需求，最终设计成一个简洁、花费少、效果好的实用型校园网。Originally design the design explaining the computer network system of the campus especially and implementation method, including systematic design principle, network technology are chosen, comprehensive wiring system, topological structure of the network and equipment selecting type, originally design the basic function that can realize each mole, meet every department's within the campus demands, design one succinct spending few, effectual practical campus network finally.

D. 关于计算机方面的英语论文 急需！！！！1000字

内容提要：本文就机房管理中如何最大限度给学生提供个性化学习空间，如何更高效地管理机房计算机介绍了七种实用技术方法。
关键词：硬盘拷贝、 硬盘还原、 网络拷贝、 多重引导、 虚拟光驱、终端服务、桌面共享
摘 要： 机械制图与计算机辅助设计CAD整合式教学具有学用结合、提高教学效果及绘图效率、培养的人才适应社会需要等优点。本文就机械制图与计算机辅助设计CAD两门课程整合的教学改革进行探讨和研究。……
关键词： 机械制图、计算机辅助设计CAD、教学改革、二维绘图、三维绘图

E. 高分跪求计算机英语论文

【英文篇名】 Switch Router Operating System Based on a General Operating System
【下载频次】 ☆
【作者】 潘登; 徐佩霞;
【英文作者】 PAN Deng; XU Pei xia （Department of Electronic Engineering and Information Science; University of Science and Technology of China; Hefei; 230027; China）;
【作者单位】 中国科学技术大学电子工程与信息科学系; 230027;
【文献出处】 数据采集与处理 , Journal of Data Acquisition & Processing, 编辑部邮箱 2003年 04期
期刊荣誉：中文核心期刊要目总览 ASPT来源刊 CJFD收录刊
【中文关键词】 交换式路由器; 通用操作系统; 路由器操作系统;
【英文关键词】 switch router; general operating system; router operating system;
【摘要】 提出了一种将通用操作系统及其上层路由软件移植到交换式路由器平台上的方案。此方案可以向上屏蔽交换式路由器与传统的路由器体系结构上的区别 ,从而把通用操作系统及其上层路由软件移植到交换式路由器的平台上 ;同时兼顾数据通信和管理维护方面的需求 ,为上层路由软件提供了与传统路由器相同的接口 ,从而使基于通用操作系统的路由软件可以在不损失可升级性的条件下快速移植到交换式路由器上。实际应用证实了该方案具有良好的灵活性和兼容性
【英文摘要】 A new solution to port general operating systems and their routing software to switch router is presented. The solution shields the architecture difference between traditional router and switch router to application level software, thus it may support general operating system and their routing software on switch router platform. The solution is also considered as requirements of both data communication and control functions. And same ways of the access and control of the router are provied as traditional ro...
【基金】 国家 8 63计划 ( 863 -3 1 7-0 1 -99)资助项目
【DOI】 CNKI:SUN:SJCJ.0.2003-04-017
【分类号】 TN915.05
【正文快照】 引 言路由器最重要的工作是根据 IP包头和路由、过滤规则转发 IP包。其他功能还包括路由表的维护与路由器系统的维护。实际上路由器可以看成是一种针对 IP网络路由需求而设计的专用计算机。随着因特网所承载的业务的演进 ,因特网对于路由器性能的要求也日渐提高。在交换式路

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文章编号: 100429037 (2003) 0420450205
一种基于通用操作系统的交换式路由器操作系统实现
潘 登, 徐佩霞
(中国科学技术大学电子工程与信息科学系, 合肥, 230027)
摘要: 提出了一种将通用操作系统及其上层路由软件移植到交换式路由器平台上的方案。此方案可以向上屏蔽
交换式路由器与传统的路由器体系结构上的区别, 从而把通用操作系统及其上层路由软件移植到交换式路由器
的平台上; 同时兼顾数据通信和管理维护方面的需求, 为上层路由软件提供了与传统路由器相同的接口, 从而使
基于通用操作系统的路由软件可以在不损失可升级性的条件下快速移植到交换式路由器上。实际应用证实了该
方案具有良好的灵活性和兼容性。
关键词: 交换式路由器; 通用操作系统; 路由器操作系统
中图分类号: TN 915105; TP393 文献标识码:A
基金项目: 国家863 计划(8632317201299) 资助项目
收稿日期: 2003203229; 修订日期: 2003206215
Switch Router Operating System Based on
a General Operating System
PA N D eng , X U P ei2x ia
(Department of Elect ronic Engineering and Info rmat ion Science,
U niversity of Science and Techno logy of Ch ina, Hefei, 230027,Ch ina)
Abstract: A new so lu t ion to po rt general operat ing system s and their rou t ing sof tw are to
sw itch rou ter is p resen ted. The so lu t ion sh ields the arch itectu re difference betw een t radit ional
rou ter and sw itch rou ter to app licat ion level sof tw are, thu s it may suppo rt general operat ing
system and their rou t ing sof tw are on sw itch rou ter p latfo rm. The so lu t ion is also con sidered as
requ iremen t s of bo th data commun icat ion and con t ro l funct ion s. A nd same w ays of the access
and con t ro l of the rou ter are p rovied as t radit ional rou ter, so rou t ing sof tw are of the general
operat ing system may be po rted to sw itch rou ter p latfo rm rap idly w ith the upgradeab le
f lex ib ility. P ract ical design app roves that the so lu t ion has a good compat ib ility and f lex ib ility.
Key words: sw itch rou ter; general operat ing system; rou ter operat ing system
引 言
路由器最重要的工作是根据IP 包头和路由、
过滤规则转发IP 包。其他功能还包括路由表的维
护与路由器系统的维护。实际上路由器可以看成是
一种针对IP 网络路由需求而设计的专用计算机。
随着因特网所承载的业务的演进, 因特网对于路由
器性能的要求也日渐提高。在交换式路由器中, 包
转发等绝大多数处理已经转移到以端口为中心的
硬件中完成, 只有路由规则的生成与维护、网络管
理和系统维护等比较复杂的工作仍由软件部分完
成。
实用中路由器所采用的操作系统可分为三大
类: (1) 以Cisco 的IO S 为代表的专用操作系统, 常
见于网络骨干节点; (2) 以V xWo rk s 为代表的嵌
入式系统, 常见于小型办公ö家用接入设备上; (3)
采用通用操作系统的则在骨干节点和用户接入设
备上都有这类设备。例如Jun iper 的路由产品就采
用L inux 作为操作系统。通用操作系统上的各种路
由、网管软件的开发已经有相当长时间, 其功能、性
能、稳定性和升级灵活性都很优秀, 但这些软件仍
第18卷第4期
2003 年12 月
数据采集与处理
Journal of Data A cquisit ion & P rocessing
Vo l. 18 No. 4
Dec. 2003
然是针对传统路由器体系结构开发的, 无法直接应
用于新的路由器体系结构。本文提出在通用操作系
统的驱动栈中插入一个中间层, 这样对系统内核及
和运行在其上的路由、网管等上层软件屏蔽了下层
硬件的特殊性, 从而把上层软件和高速硬件平台结
合起来。该方案已经应用于高速边缘路由器中, 并
表现出了良好的实用性和可扩展性。
1 交换式路由器与传统路由器在体
系结构上的差别
路由器工作在网络的第三层, 其处理工作主要
涵盖七层模型中的下三层, 包括: 物理接口处理、数
据链路层处理、网络层的路由查找、转发以及队列
管理等[1 ]。在传统的路由器体系结构中, 硬件部分
只实现物理层的处理, 其余工作需要消耗系统计算
资源完成: 包括CPU 周期、内存容量和总线带宽
等, 因此性能也受限于这些资源。而在交换式路由
器中, 路由处理机仅处理系统维护、路由表维护等
少量工作, 数据流的处理都由相对独立的硬件完
成, 不再受限于系统计算资源, 因此其性能远优于
传统路由器[2 ]。如图1 所示。
(a) 传统路由器体系结构
(b) 交换式路由器体系结构
图1 路由器的逻辑结构
传统路由器和交换式路由器在体系结构方面
有明显的区别: 在传统路由器中, 所有的物理接口
直接挂接在总线上, 内核可以通过总线直接访问这
些接口; 而在交换式路由器中, 只有控制卡是直接
挂接在总线上的, 内核必须通过控制卡间接访问各
个接口。这导致操作系统内核中代表网络接口的驱
动对象的区别: 在传统路由器中, 内核存在若干网
络设备驱动对象实例, 每个实例通过总线直接维护
一个端口, 为内核及其上面的上层软件提供基本操
作支持。而在交换式路由器中, 普通的网络设备驱
动对象无法直接维护端口, 也无法支持系统内核和
上层软件操作。因此, 交换式路由器体系结构的特
殊性使得通用操作系统和上层软件无法直接应用。
针对这个问题有两种解决办法: (1) 大量修改内核
和各种相关软件的源代码以适应新的体系结构。这
种做法存在开发工作量大、周期长、局限性强的缺
点, 丧失了使用通用操作系统的灵活性; (2) 在驱动
栈中增加一个中间层, 支持普通网络驱动对象所能
支持的一切操作, 这样系统内核和上层软件基本上
不必修改就可以运行在交换式路由器上。这就是本
文所提出的中间层方案。这种方案克服了第一种方
法的复杂性, 在保持灵活性的基础上, 可以快速地
把通用操作系统及上层软件移植到交换式路由器
的硬件平台上。
2 中间层设计
中间层功能包括数据通信和控制两个方面。从
数据通信方面考虑, 每个端口的功能都等效于传统
路由器中的一个网络接口, 所以每个物理端口在内
核中都应有对应的网络驱动实例。这样才能支持各
种上层软件运行, 满足数据通信功能的需要。
从控制功能方面考虑, 对上要把每一种可能的
逻辑操作映射成硬件操作; 对下要能够和多个设备
通信。上层应用包括系统维护、路由软件、网管软
件; 下层设备包括处理引擎和端口。控制功能的具
体实现和硬件平台有关。考虑到多种应用可能同时
操作一个硬件设备, 一种应用也可能同时操作多个
设备, 在实现时必须考虑到对于多并发操作的支
持。
基于上述考虑, 中间层由控制卡驱动模块和若
干网络驱动实例组成。在图2 (a, b) 中分别给出了
传统路由器的结构与驱动方式以及本文所提出的
中间层所处的位置与驱动方式。
第4 期潘 登, 等: 一种基于通用操作系统的交换式路由器操作系统实现451
图2 中间层的位置与驱动方式
控制卡驱动模块作为中间层的核心, 维护控制
卡上所有的端口、内存映射、中断和循环缓冲队列
资源。它实现了数据通道和控制通道。对下直接驱
动控制卡、与各个端口、处理引擎通信; 对上, 一方
面通过内核调用陷阱方式提供控制通道接口; 另一
方面向虚拟网络驱动实例提供数据通道接口。虚拟
网络驱动实例在操作系统内核为各个物理端口实
现网络驱动实例。它们工作在控制卡驱动模块的基
础上, 并不直接控制硬件, 故称为虚拟网络驱动实
例。虚拟网络驱动实例封装控制卡驱动模块提供的
数据传输功能, 并为内核和上层软件提供与普通网
络驱动实例相同的调用接口。下面分别给出数据通
道和控制通道的实现方案。
211 数据通道的功能与实现
虚拟网络驱动实例和物理端口是一一对应的。
内核数据收发的功能包括3 个方面:
(1) 发往某虚拟网络驱动实例的数据包应该由
其对应端口输出;
(2) 这个端口所收到的包也通过该虚拟网络驱
动实例向系统内核提交;
(3) 中间层也可以对虚拟网络驱动实例进行流
控操作, 以避免因拥塞导致数据丢失。
注意到图2 (b) 中的交换结构以定长信元交换
数据, 其格式如图3 所示, 其中信元头占4 字节, 包
括处理引擎号和端口号域。对于收ö发信元, 处理引
擎号和端口号分别为该信元的源端口的和目的端
口的对应值。
根据图2 (b) 所示的系统结构可知: 由处理引
擎号和端口号可以确定端口的物理位置。控制卡驱
动模块在其内部的驱动信息数组中维护虚拟网络
驱动实例和端口之间的对应关系。
图3 数据信元结构
发送数据时, 虚拟网络驱动实例从内核网络部
分获取待发送的数据, 偕同指向该实例自己的指针
一起提交给控制卡驱动模块。一方面, 控制卡驱动
模块通过这个指针可以对虚拟网络驱动实例进行
流控设置; 另一方面, 控制卡驱动模块根据虚拟网
络驱动实例指针查驱动信息表得到目标端口物理
位置信息, 包括处理引擎号和端口号。端口物理位
置信息将被填充到所有用来承载待发送数据包的
信元头中。控制卡驱动模块通过控制卡把信元送到
交换结构, 而交换结构和处理引擎分别根据处理引
擎号和端口号将信元转发到到目标端口。最后端口
从接收到的信元中恢复出原始数据发出。
接收数据时, 端口也会将数据拆分到若干信元
中逐级上传。考虑到交换结构的循环优先机制, 一
个数据包上传的过程可能被来自其他端口的数据
抢断。所以控制卡驱动模块对于接收到的信元按源
端口位置信息(包括处理引擎号和端口号) 保存到
不同的缓冲区中。当接收到该数据包相关的全部信
元, 控制驱动模块即可重组该数据, 并根据源端口
位置信息查驱动信息表以得到指向该端口对应虚
拟网络驱动实例的指针, 进而激活该虚拟网络驱动
实例接收数据。虚拟网络驱动实例从控制卡驱动模
块中获取数据后, 按照网络驱动的常规方式调用
net if- rx 接口向内核提交数据。数据收发实现结构
如图4 所示。
值得注意的是, 在交换式路由器中, 处理引擎
通过交换结构交换的是IP 包; 而通用操作系统中
452 数据采集与处理第18 卷
图4 数据收发实现结构
网络驱动通常处理链路层的帧。即控制卡驱动模块
数据通道对上对下的数据格式是不同的。因此, 在
发送数据时控制卡驱动模块需要从得到的链路帧
中提取IP 包再转发到端口; 而接收数据时则对来
自端口的IP 包进行链路帧封装再向上提交。以以
太网为例, 需要恢复的包括源和目标站的物理地
址、载荷类型和帧校验[3 ]。对于承载IP 包的以太
帧, 显然其目标站物理地址和载荷类型[4 ]都是已知
的。实现时采用的操作系统是L inux, 通过在虚拟
网络驱动源代码中进行设置可以使内核不进行帧
校验[5 ]。所以只有源站物理地址未知。如果要求硬
件给出真实的源站物理地址, 则增加了硬件的复杂
度; 而若在控制卡驱动模块中伪造源物理地址, 则
可能导致内核的ARP 管理混乱。为简化硬件设
计, 实现时采用了在控制卡驱动模块中伪造源物理
地址的办法, 同时修改虚拟网络驱动源代码, 重载
帧头处理函数[6 ]。这样内核ARP 表就不受伪造地
址的影响, 其获取和刷新通过查询端口ARP 记录
实现。
212 控制通道的功能与实现
控制功能的通信也是基于信元的, 其操作包括
维护管理和表同步两类。维护管理主要是进行各种
查询, 通常通过若干次双向通信完成。每次通信有
效载荷都只有几个字节, 由一个信元即可承载。而
表同步则是将上层软件维护的表复制到相关硬件
中, 包括ARP 表、路由和分类表等。表同步操作涉
及大量数据传输, 需要由多个信元承载。控制功能
都是针对设备进行的, 所以在控制ö反馈信元中也
必须包括目标设备的物理位置信息。
在实际运行期间, 所有的上层应用和设备之间
的控制通信复用控制通道, 其特点为:
(1) 不同的应用可能同时访问同一设备;
(2) 一个应用也可能同时访问多个设备;
(3) 同一应用对于同一个设备的操作一般都是
顺序的。
为支持这种复用操作, 所有承载控制信息和反
馈信息的头部除包括目标硬件的物理位置和操作
指令外, 还包括命令类型、应用类型信息。控制ö反
馈用信元结构如图5 所示。
图5 控制ö反馈信元结构
图5 中: 处理引擎号和端口号, 确定设备的物
理位置; 收ö发信元分别为该信元的源端口的和目
的端口的对应值; 命令码在设备和应用之间定义。
每种可能的操作分配一个代码; 应用码在控制卡驱
动模块和上层应用之间预定义。每种可能的应用分
配一个代码。这些应用包含网管、路由维护、硬件维
护和ARP 信息获取等。
上层应用通过内核调用陷井( IOCTL ) 发起控
制通道操作, 同时给出目标设备物理位置、命令类
型代码和应用类型代码。控制卡驱动模块把这些信
息填充到控制信元中再将其发往设备。设备把这些
代码直接复制到反馈信元中, 再在后面追加上反馈
信息。控制卡驱动模块为每一种应用分配一个循环
缓冲区, 把收到的反馈根据应用类型排入相应队列
中。上层应用从其所对应的循环缓冲区中读取反馈
信元, 然后根据信元中的物理位置信息、命令码就
可以确定该反馈对应的原始命令, 从而对反馈数据
进行适当处理。这样就实现了各种控制功能对控制
通道的复用。如图6 所示。
第4 期潘 登, 等: 一种基于通用操作系统的交换式路由器操作系统实现453
图6 控制通信实现结构
3 结 论
鉴于传统路由器体系结构和交换式路由器体
系结构的区别, 通用操作系统及在其上开发的路由
软件无法直接应用于交换式路由器。本文提出的中
间层方案可以有效地解决这个问题。该方案全面考
虑了数据通信和管理维护方面的需求, 为上层提供
了与原有模型基本相同的接口, 并使得路由软件在
不损失其灵活性和可升级性的条件下直接应用于
交换式路由器中。虽然该方案只是在特定的平台和
特定的操作系统上得到了实现, 但是不难看出, 这
种思路对操作系统并没有特殊的依赖性, 完全可以
移植到其他通用操作系统上。本文提出的方案已经
在国家863 项目实用化综合接入系统的高速边缘
路由器的研制中取得了良好的实际效果。本文为国
产高性能路由器的软件开发提出了一种高效快捷
的解决方案, 该方案具有良好的应用前景。
参考文献:
[1 ] Kuro se J F, Ro ss KW. Computer netwo rk ing: a top2
dow n app roach featuring the internet [M ]. A ddison
W esley Longman′s P ress, 2001. 332～ 341.
[ 2 ] 梁阿磊, 等. 路由器体系结构及其发展[J ]. 小型微型
计算机系统, 2001, 8: 943～ 945.
[3 ] M edia access cont ro l frame st ructure [S ]. IEEE Std
80213, 1998. 36～ 40.
[ 4 ] Charles Ho rnig. RFC 894: a standard fo r the t rans2
m ission of IP datagram s over Ethernet netwo rk s[S ].
198411～ 2.
[5 ] Bovet D P. U nderstanding L inux kernel[M ]. O reil2
ley P ress, 2002. 683～ 685
[ 6 ] Rubini A. L inux device drivers. 2nd edit ion [M ].
O r2eilley P ress, 2001. 455～ 458
作者简介: 潘 登(19772) , 男, 博士研究生, 研究方向: 网络
体系结构、网络安全, E2mail: pandeng@mail. ustc. e. cn;
徐佩霞(19412) , 女, 教授, 博士生导师, 研究方向: 音频视频
编码、非线性处理、下一代网络。
454 数据采集与处理第18 卷

F. 跪求一遍关于计算机网络的英语作文..字数在1200以上的..

Computer networks
Now every almost have computers, and computer good does have its downside - it depends on how you use. If you want to ask me: I on the computer do what, I can tell you, I will do a lot of things in the computer. May first and have out-of-town relatives chat, then can check information, listening to music, watching movies, paint... My favorite on the computer music and watching movies, because it very relaxing my mood.But the most people used compter to surf the internet.Now Let us know about the computer network
Ⅰ.Introction
Computer networks,the wide spread sharing of information among groups of computers and their users,are a central part of the information age.The popular adoption of the personal computer(PC)
and the local area network (LAN) ring the 1980s has led to the capacity to access information on a distant database;download an application from overseas;send a message to a friend country;and share files with a colleague-all from a personal computer.
The network that allow all this to be done so easily are sophisticated and complex entities.They rely for their effectiveness on many cooperating computers.The design and deployment of the wordwide computer network can be viewed as one of the great technological wonders of recent decades. Nowadays Intemet is very popular all over the world, especially in some big cities. Do you know when the Intemet was first established? Built in 1960s, the Internet was a crude network of a few computers which shared information. If one of the computers broke down, the whole networks would be unable to work, causing continual problems. At first, just the government had access to the Internet, using it for communications among different branches. However, by 1970s the Internet had been used in universities, banks, and hospitals. At the beginning of 1990s computers became affordable for common people and this affordability increased the use of the Internet by people,It is said that each day tens of millions of people log off, making it the most important part of people's life.

Ⅱ.Local Area Network
One of the most dramatic events in computer networking has been the introction and rapid growth of local area network(LAN) as a way to standardize the system of linking computers used in office systems.As the name suggests,this is a means of connecting a number of computing elements together.At the simplest level,a LAN provides no more more than a shared medium (such as a coaxial cable to which all computers and printers are connected) along with a set of rules that govern the access to that medium.The most widely used LAN,Ethernet,used a mechanism called Carrier Sense Multiple Access-Collosion Detect(CSMA-CD).This means that each connected device can only use the cable when it has established that each connected device is using it.If there is contention, the device looking for a connection backs off and tries again later.The Ethernet transfers data at 10M bits/sec,which is fast enough to make the distance between devices insignificant.They appeat to be connected directly to their destination.
There are many different layouts(such as bus ,star,ring,see Figure 6A-2)and a number of different access protocols for LANs.Despire this variety,all LANs share the feature that they are limited in range (typically they cover one building) and are fast enough to make the connecting network invisible to the devices that use it.
In addition to providing shared access,modern LANs can also give users a wide range of sophisticated facilities.Managenment software packages are available to control the way in which devices are configured on the local area network (LAN),how users are administered,and how network resources are controlled.A widely adopted structure o local network is to have a number of servers that are available to a (usuallu much greater) nember of clients.The former,usually powerful computers,provide service such as print control,file sharing,and mail to the latter,which are usually personal computers.
Ⅲ.Routers and brideges
The facilities on most local area network (LAN) are very powerful.Most organizatonns do not wish to have small isolated islands of computing facilities.They usually want to extend facilities over a wider area so that groups can wok wtthout having to be located.Routers and bridges arespecialized devices that allow two or more local area network (LAN) to be connected.The bridges is the more basic device and can only connect local area network (LAN) of the same type.The router is a more intelligent component that can interconnent many different types of computer network.
Many large companies have corporate adta network that are founded on a collection of local area network (LAN) and routers.From the user’s point of view,this arrangement provides them with a physically diverse network that looks like one coherent resource.
Ⅳ.Wide Area Networks
At some point,it becomes impractical to extend a local area network (LAN) any further.Physical limitation sometimes drives this,but more often than not there are more concenient or cheaper ways to extend a computer network.Two major components in most real computer networks are the public telephone and data networks.These provide long-distance links that extend a local area network (LAN) into a wide area network (WAN).Nearly all of the national network operators offer services for the interconnection of computer networks.These services range from simple, low speed data links that work over the public telephone network to sophisticaied high speed data services that are ideally suited to the interconnection of LANs.These high speed data services are usually referred to as broadband connection.It is anticiopated that they will provide the necessary links between LANs that make what is called the information superhighway a reality.