CHAPTER 6 THE INTERNET
第6章 因特网
  Main Points:
  ● About The Internet
  ● Connecting Internet
  ● Applications of The Internet: WWW and E-mail
  ● Security and Future of The Internet
  主要学习内容:
  ● 关于因特网
  ● 连向因特网
  ● 因特网应用:万维网和电子邮件
  ● 因特网的安全和今后的发展

6-1 THE INTERNET COMMUNITY TODAY
第1节 今日的因特网实体

  Ⅰ. Objectives :
  Introduce the major members enjoyed the use of the Internet and describe their function and position briefly.
  本节的主要目标是:
  本节介绍了享用因特网的主要成员,并简述了他们的作用和地位
  学习主要词汇:

  Ⅱ. Key words :
  community  团体,社区,共同性
  digital divide   数字鸿沟
  ISP(Internet Service Provider)   因特网服务提供商
  access    接入,访问
  Web page     (万维网)网页
  Web site     (万维网)网站
  ICP (Internet Content Provider)    因特网内容提供商
  ASP (Application Service Provider)    应用业务提供商
  browser    浏览器

  Ⅲ.Reading and comprehension
  课文重点内容的阅读和理解
  ◆ Paragraph 1 : About users
  第1段 :关于用户
  The Internet community today is populated by individuals, companies, and a variety of organizations located throughout the world (see Fig.6-1).[1] Virtually anyone with a computer that has communications capabilities can be part of the Internet, either as a user or as a supplier of information or services. Most members of the Internet community fall into one or more of the following groups.
  1. Users
  Users are people who avail themselves of the vast amount of resources available through the Internet at work or in their personal lives.[2]There are well over a hundred million Internet users in the U.S.A alone and they come from all walks of life. The USA. digital divide—the disproportionate higher level of Internet use for certain groups of individuals (typically the more affluent and more educated)—is lessening as free Internet access is becoming more widespread in libraries, schools, and other public locations.[3]
  这一段有两个问题需要解释:
  ① avail 为动词,为有价值,有帮助\裨益于。固定搭配用法为 avail oneself of……,利用,乘……之便的意思,本句中who引导的是定语从句
  ② The USA. digital divide— 这是一个长句,两个波折号之间是同位语,是对 digital divide 的解释,as 引导的是原因状语从句
  ◆ Paragraph 2 : About ISPs
  第2段 :关于因特网服务提供商
  2.Internet Service Providers
   Internet Service Providers (ISPs)—often called service providers or access providers for short—are organizations that provide Internet access to others. They operate very much like a cross between cable-television and phone companies in that they provide access to a communications service, usually for a monthly fee.[4]
  In addition to Internet access, ISPs furnish subscribers with E-mail addresses so they can exchange electronic mail. Many providers will also allow these individuals to post personal Web pages on the provider’s Web site at no additional cost.

Fig. 6-1 The Internet community
  该段请注意They operate very…… 这一句中,cross 为交叉连接,in that 引导的是方式状语从句。
  ◆ Paragraph 3 : About ICPs
  第3段 :关于因特网内容提供商
  (此段无解释)
  3.Internet Content Providers
  Internet Content Providers, or content providers, are the parties that furnish the information available through the Internet. Here are some examples of content providers:
  ·A photographer creates electronic copies of some of her best work and places them along with her E-mail address and phone number on the Internet.
  ·A software company creates a Web site that users can access to both get product information and download trial copies of software.
  ·A television network sponsors a site for its newest reality TV show, including statistics, photographs, and live video feeds.
   Paragraph 4 : About ASPs
  第4段 :关于应用服务提供商
  (此段无解释)
  4. Application Service Providers
  Application Service Providers (ASPs) are companies that manage and distribute software-based services and solutions to customers across a network—usually the Internet. Instead of providing access to the Internet like ISPs do, ASPs provide access to software applications. In essence, ASPs rent software access to companies or individuals. Just as with Internet access, customers typically pay a monthly or yearly fee to use the applications.
  ◆ Paragraph 5 : About infrastructure companies
  第5段 :关于基础设施公司
   5.Infrastructure Companies
   Infrastructure companies are the enterprises that own or operate the paths or “roadways” along which Internet data travel.[5] Included in this group are phone and Internet-backbone companies, cellular, satellite, and cable-TV companies, and the like.[6]
  请注意第一句话中,修饰 the enterprises 的,由that 引导的定语从句中,又有由along which 引导的定语从句
  ◆ Paragraph 6 : About hardware and software companies
  第6段 :关于硬件和软件公司
  6. Hardware and Software Companies
   In addition to the types of companies covered thus far, a wide variety of hardware and software companies make and distribute Internet-related products. The firms that supply browser and E-mail software fall into this category. So, too, do the companies that make modems, routers, servers, PCs, server software, and Web-publishing tools.[7] The customers of software and hardware companies are users, service and content providers, and infrastructure companies.
  这一段中请注意The firms that……category 这句话和下面的So, too, do… 这句话,在内容上有关联,前一句是“提供浏览器和电子邮件软件的公司属于这个范畴”。而后一句用do代替上句中的fall into this category. 主语是the companies that 引导的是定语从句,修饰companies
  ◆ Paragraph 7 : Other members in the Internet community—the government and other organizations
  第7段 :因特网实体中的其他成员—政府和其他机构
   7. The Government and Other Organizations
   Many other organizations influence the Internet and its uses. Governments have among the most visible impact; and their local laws limit both information content and access in the Internet community. The Internet Society is another key organization.[8] This professional membership society provides leadership in addressing the issues that affect the future of the Internet, and it also oversees Internet infrastructure standards, such as which protocols can be used and how Internet addresses should work.[9]
  这一段中有两个词的用法需要解释:
  ① among 通常的用法为在……中间,但也作(同类)之一讲,如本句Governments have among the most visible impact; 即为政府也是最有影响的单位之一。
  ② addressing 此处作提出解,如They addressed their questions to the teacher:他们向老师提出问题。This professional membership…… 这一长句中,由and 连接两个并列句。in addressing 为介词短语作定语,而that 引导的是定语从句,修饰issues

  NOTES
  [1] populate 居住于…, 常用于被动式。此处可译为由…组成。
  [2] avail themselves of, 此处为利用。
  [3] 长句。as引导的是原因状语从句。
  [4] in that引导的是方式状语从句。
  [5] 句中有两个定语从句,分别由that和 along which引导。
  [6] cellular此处系指cellular radio telephone蜂窝式无线电话,或cellular mobile telephone蜂窝式移动电话。
  [7] do 代替前一句中的fall into this category。
  知识点:do代替上句中出现的动词,甚至包括该动词后的有关句子成分的用法举例:
  Copper wire allows a larger current than does iron wire.
  铜线比铁线能允许通过更大的电流。
  [8] Internet Society是因特网行业组织。
  [9] 由and连接的并列句。in addressing 为介词短语做定语,而that引导的定语从句,修饰issues。addressing原意为“提出”。
  知识点:address用做“提出”时的用法举例:
  they addressed their questions to the teacher.
  他们向老师提出问题。

  Ⅴ. Exercises
  Multiple Choices
  1. Today the members of the Internet community include ( )
  a. companies
  b. organizations
  c. universities
  d. individuals
  2.( )can be a member of the Internet community
  a. a supplier of information
  b. a supplier of services
  c. a person without a computer
  d. a person with a computer
  3. The digital divide in U.S. is lessening because free Internet access is becoming more widespread in( )
  a. network bars
  b. schools
  c. libraries
  d. other public locations
  4. Many Internet Service Providers provide( )
  a. Internet access to others
  b. hardware-based services
  c. E-mail services
  d. Web page services
  5. The following supplier is the Internet Content Provider( )
  a. television network
  b. photographer
  c. software company
  d. hardware company
  6. Application Service Providers provide( )
  a. access to the Internet like ISPs
  b. software-based services
  c. software-based solutions
  d. application services charged monthly or yearly
  7.( )companies belong to the infrastructure companies
  a. cable-TV
  b. cellular
  c. phone
  d. Internet-backbone
  8. Software companies offer the following products that are Internet-related ones( )
  a. modems
  b. E-mail software
  c. Web-publishing tools
  d. browsers
  9. Hardware companies offer the following products that are Internet-related ones ( )
  a. modems
  b. routers
  c. server software
  d. .PCs
  10. Responsibilities of the Internet society include ( )
  a. addressing the issues that affect the future of the Internet
  b. supervising Internet infrastructure standards
  c. overseeing the use
  d. working as an ISP

6-2 CONNECTING TO THE INTERNET
第2节 连向因特网

  Ⅰ. Objectives :
  Understand three factors concerning the Internet connectivity, they are type of device type of connection and type of ISP.
  本节的主要目标是:
  了解涉及连向因特网的三个因素,即设备类型,连接类型和因特网服务提供商的类型

  Ⅱ. Key words :
  portability    便携(设备)
  animation    动画
  video chip    视频剪辑
  mobile Web    移动万维网
  wireless Web    无线万维网
  notebook    笔记本(电脑)
  handheld    手持的
  built-in    内置的
  mobile phone    移动电话
  pager    寻呼机
  modem    调制解调器
  video on demand (VOD)    视频点播
  premise    前提,处所
  tree topology    树型拓扑
  optical fiber    光纤
  WAN (Wide Area Network)    广域网
  LAN (Local Area Network )    局域网
  dedicated connection     专线连接
  wireless connection    无线连接
  transceiver    收发器
  coaxial cable     同轴电缆
  cable TV    有线电视
  ADSL(Asymmetric Digital Subscriber Line)    非对称数字用户线
  downstream    下行,顺流,下游
  upstream    上行,逆流,上游
  CO(Central Office)    中心(交换)局
  HFC(Hybrid Fiber Coax)    混合光纤同轴电缆(网)
  MSO(Multiple System Operator)    多系统运作员
  head end    头端器,数据转换器
  RF (Radio Frequency )    射频,无线电频率
  cable modem    电缆调制解调器
  backbone network    主(骨)干网
  duplex    双工

  Ⅲ.Reading and comprehension
  课文重点内容的阅读和理解
  一. Part 1 Type of Device
  第一部分 设备类型
  Connecting to the Internet usually involves three decisions. The first is determining the type of device you will use to access the Internet. The second is selecting the type of connection desired. A final step is deciding on the type of Internet service provider required. Once these determinations have been made, an ISP can be selected and your computer can be set up to access the Internet.
  1. Type of Device
  The Internet today can be accessed by a variety of devices. The type of device used depends on a combination of factors, including the amount of portability needed and the desired content to be retrieved from the Web. There three types of the device.
  (1) PCs
  Most users who have access to a PC at home, work, or school will use it to access the Internet, when needed.[1] One advantage of using PCs for Internet access is that they are usually fast and can be connected to high-speed Internet connections. They also can be used to retrieve virtually any content from the Web, including pages with multimedia content, such as animation, music files, and video clips. A final advantage is that they usually have access to a printer and hard drive, so Web pages and E-mail messages can be printed, and E-mail and downloaded files can be saved when needed.
  (2) Internet Appliances
  Internet appliances are designed specially for accessing the Internet, especially in homes that don’t have a PC.
  (3) Mobile Devices
  Mobile Web use—or wireless Web, as it is frequently referred to—is one of the fastest growing Web applications today. Notebook and handheld devices frequently use attached or built-in modems to access the Internet; and most mobile phones and pagers have Internet connectivity built in.
  这一部分没有复杂和疑难的句子,但需要注意have access 的用法,如Most users who have access to a PC…… 这句话中who 引导的定语从句,修饰users ,have access to 为接触或使用
  二.Part 2 Type of connection
  第二部分 连接类型
  ◆ Paragraph 1 : Dial—up connections
  拨号连接
  2. Type of Connection
  (1) Dial-Up Connections
  Dial-Up Connections usually work over regular telephone lines. To connect to the Internet your modem (or other appropriate interface device) dials up and connects to a modem attached to your ISP’s computer.[2] While you are connected, your PC is assigned a temporary IP address for the current session.[3] At the end of each Internet session, you disconnect from your ISP’s computer to allow another user to connect in your place.[4] Standard dial-up Internet service uses a conventional dial-up modem rated at a maximum data transfer rate of 56Kbps.
  这一段注意从While you are connected, 开始的两句话是相关联的。其中第一句由While引导的时间状语从句,且为被动语态,实际上是你的PC机被连入网了。并且由ISP为你的PC机指派一个临时IP地址。第二句是在会话结束时,要断开与ISP计算机的连接,以便允许其他用户用你的地方进行连接,实际上是进行连接后使用你的IP地址。
  ◆ Paragraph 2 : ADSL Connection
  第2段 :非对称数字用户线连接
  (2) ADSL Connection
  Another type of dial-up connection is ADSL, which is the most common way to access the Internet today. Sometimes ADSL is called as broadband accessing, because it provides more wide bandwidth than that the regular modem provides.ADSL was first developed in the 1980s as the telecommunications industry’s answer to the cable industry’s request to support video on demand. In the middle 1990s, however, it was quickly recognized as a viable technology to enable access to high-speed services such as the Internet[5]. ADSL delivers asymmetric transmission rates typically up to 9Mbps downstream (from the CO to the premises) and 16Kbps to 640 Kbps upstream (from the premises to the CO) as shown in Fig. 6-2. Like all copper transmission systems, the higher the bit rate, the shorter the range. A limitation of ADSL transmission is distance: it can only be used within three miles of a telephone switching station, and the speed degrades as the distance gets closer and closer to the three-mile limit.
  ① 请注意it 作为先行主语,而实际的主语是to enable access…… ,这种句型经常出现
  ② 注意本段最后一句话it can only be used…… 中gets closer and closer to the three-mile limit. 的用法,是指越是接近3英里,速度越降低
  ◆Paragraph 3 : HFC Technology
  第三段:混合光纤同轴电缆技术
  (3) HFC Technology
  HFC technology is based on existing cable television (cable TV or CATV) technology. Originally, cable TV systems were based on coaxial cable facilities from an MSO to a customer premises and used a tree topology. Most of these systems have been upgraded to HFC, by which the signal is brought to a fiber node via a pair of optical fibers and then distributed via coaxial cable to customers, as illustrated in Fig. 6-3.[6]At the head end, signals from various sources, such as traditional satellite services, analog and digital services using WAN, and Internet service provider (ISP) services using private backbone network, are multiplexed and converted up from an electrical (radio frequency) signal to an optical signal[7]. Communication is one way on the optical fiber;and each of a pair of optical fibers from the head end to the fiber node carries one-way traffic in opposite directions. The optical signal is converted down to RF at the fiber node and travel over the coaxial cable in a duplex mode. The signal going from the head end to the customer premises is called a downstream signal or a forward path signal. The signal going from the customer premises to the head end is called an upstream signal or a reverse path signal.

  Fig. 6-2 ADSL architecture
  这一段有2个问题需要解释:
  ① Most of these systems…… ,by which 引导的是非限定性定语从句,说明信号经过HFC的情况。
  ② At the head end,…… 这是一句长句,主句是signals…… ,are multiplexed and converted…… ,中间插入such as 引导的同位语。
  Paragraph 4 : Dedicated Connection
  第四段:专线连接
  (4) Dedicated Connection
  Unlike dial-up connections that only connect to your ISP’s computer when you need to access the Internet, dedicated connections keep you continually connected to the Internet. With a dedicated connection, your PC is typically issues a static (non-changing) IP address to be used to transfer data back and forth via the Internet.
  Types of dedicated Internet connections include connecting through a school or office LAN, as well as ADSL, cable, satellite, and fixed wireless connections.
  这一段Unlike dial-up connections…… 句中Unlike 引导的是条件状语,其中从属连词that 连接的 only connect to…… 是同位语, when 引导的是时间状语从句
  ◆ Paragraph 5 : Mobile Wireless Connection
  第五段:移动无线连接
  (5) Mobile Wireless Connection
  Unlike satellite and fixed wireless connections, which use a cable to connect the modem to some type of fixed transceiver, mobile wireless connections allow the device to be moved from place to place. Consequently, most handheld PCs and other mobile devices (like Web-enable cell phones) use a mobile wireless connection and access the Internet through the same wireless network as cell phones and messaging devices.
  3. Type of Internet Service Provider (See 6-1 of this chapter please !)
  该段第一句话仍以Unlike 引导的条件状语开始,但后面有which 引导的非限定性定语从句做进一步解释,主句是mobile wireless connections……

Fig. 6-3 An HFC network

  Ⅳ. Summary :
  Describe the Internet connectivity in two respects: type of device and type of connection.
  小结:本节叙述了连接因特网的两方面问题 : 设备类型和连接类型
  Ⅴ. Exercises
  Multiple Choices
  1. Connecting to the Internet usually includes the following decisions type of( ).
  a. device
  b. connection
  c. user
  d. Internet service provider
  2.Which device can be used to access the Internet? ( ).
  a. PC
  b. DVD
  c. notebook computer
  d. Internet appliance
  3. Following device belongs to the one of dial-up connection ( ).
  a. HFC
  b. modem
  c. dedicated line device
  d. ADSL
  4. Using a PC we can retrieve much contents from the Web, they are ( ).
  a. Web pages
  b. multimedia contents
  c. video clips
  d. music files
  5. Mobile Web is used for( )usually
  a. notebook computers
  b. mobile phones
  c. handheld computers
  d. pagers
  6. When we use a dial-up connection to access the Internet, we need( ).
  a. a TV cable
  b. a regular telephone line
  c. a modem
  d. a temporary IP address
  7. ADSL works at a rate of ( ).
  a. asymmetric transmission
  b. symmetric transmission
  c. asymmetric transmission with 9Mb/s downstream
  d. asymmetric transmission with 16K-64Kb/s upstream
  8. We can find the following facilities in an HFC system ( ).
  a. optical fiber b. coaxial cable
  c. cable modem d. head end
  9. With the dedicated connection to connect the Internet we should ( ).
  a. use dial-up connection
  b. keep a continual connection
  c. use a static IP address
  d. keep a temporary connection
  10. If some one wants to use mobile wireless connection, he or her should have ( ).
  a. mobile device
  b. a fixed radio connection
  c. Web-enable cell phone
  d. a mobile transceiver

6-3 WORLD WIDE WEB
第3节 万维网

  Ⅰ. Objectives :
  Understand the basic architecture of WWW and its use
  本节的主要目标是:
  了解万维网的基本结构以及它的使用

  Ⅱ. Key words :
  WWW (World Wide Web)    万维网
  Web browser    万维网浏览器
  application layer    应用层
  software package    软件包
  Netscape navigator    网景公司导航器
  Microsoft IE (Microsoft Internet Explorer) 微软公司因特网浏览器
  URL (Uniform Resource Locator)    统一资源定位器
  Home page    主页
  HTTP (Hypertext Transfer Protocol)    超文本传输协议
  software suite    软件套件
  search engine    搜索引擎

  Ⅲ.Reading and comprehension
  课文重点内容的阅读和理解
  Paragraph 1 : The basic architecture and work of the WWW
  第一段: 万维网的基本结构和工作原理
  1. World Wide Web
  The World Wide Web (also known as WWW or Web) is one of the fastest-growing Internet software applications. It is an architectural framework[1] for accessing linked documents spreading out over thousands of machines all over the Internet.
  Fig.6-4 shows how the Web works. Each client computer needs an application layer software package called a Web browser. Netscape navigator and Microsoft Internet Explorer are the most popular browsers. Each server on the network needs an application layer software package called a Web server. There are many different Web servers, such as those produced by Netscape, Microsoft, and Apache.

Fig.6-4 Web browsers and servers.
  In order to get a page from the Web, users must type the Internet Uniform Resource Locator (URL) for the desired page, or must click on a link that provides the URL[2]. The URL specifies the Internet address of the Web server, the directory, and name of the specific page wanted. If no directory or page is specified, the Web server will provide whatever page has been defined as its home page. If no server name is specified, the Web browser will presume the address is on the same server and directory as the last request[3].
  In order for the requests from the Web browser to be understood by the Web server, they must use the same standard protocol. If there was no standard and each Web browser used a different way to request pages, then it could be impossible for a Netscape Web browser to communicate with a Microsoft Web server, for example.
  The standard protocol for communication between a Web browser and a Web server is Hypertext Transfer Protocol (HTTP).
  请注意If no directory……as its home page 这一句话,If 引导的是条件状语从句,主句中whatever page 为宾语从句
  下一句If no server name……as the last request[3]. 这一句话,主句中 the address is…… 也是宾语从句,只不过在 presume 后面省略了that
  ◆ Paragraph 2 : About MS—Internet Explorer
  第2段 : 关于微软公司的因特网浏览器
  2.About MS-Internet Explorer
  Internet Explorer is Microsoft Corporation’s Web software suite. It provides all the tools you need to communicate, share, and access information on the World Wide Web. Michelle plans to use Internet Explorer at the workshop because it is easy to use and understand.
  Michelle provides the following overview of the tools available in various installations and versions of Internet Explore. She emphasizes that you shouldn’t worry if you don’t understand the functions of each tool right now. You’ll learn more about individual Internet Explorer tools later. Table 6-1 lists some services Internet Explorer provides. Which Internet Explorer tool your computer has, however, depends on how Internet Explorer was installed on your computer[4].  
Table 6-1 Internet Explorer Tools
  SERVICE   INTERNET EXPLORER TOOLS
  
Internet Explorer and Internet Tools
  Browser that retrieves, displays, and organizes documents. These documents are retrieved from Web servers and appear on your computer monitor. Internet Explorer includes searching and organizing features that help you keep track of information on the Web and built-in intelligence that automates many common Web tasks.
  
Internet Explorer
  Web accessories
  Kit that makes Web browsing even easier. Includes ability to view single frames, simplify searches, zoom in and out of Web page images, highlight text, view all the links on a page, and more.
  
Outlook Express
  E-mail and newsgroup manager that lets you send, receive, compose, edit, search, and sort e-mail. E-mail, or electronic mail, is a note you write and send across the Internet. Outlook Express can handle e-mail containing practically any file type—graphics, sounds, videos, and so on, Outlook Express also functions as a newsgroup manager helps that helps you participate in a discussion group.
  
Windows Media Player
  Windows Media Player lets you receive and play most media types on the Internet, including audio, video, and mixed-media files.
  
Chat
  Microsoft Chat is an Internet chat program that lets you chat with a comic strip.
  
NetMeeting
  NetMeeting lets you participate in online conferences in which you can share documents over the Internet.
  
Wallet
  Stores credit card and address information in a secure “wallet” on your computer so you can easily and safely shop on the Internet.
  
FrontPage Express
   FrontPage express is a Web-page editor that lets you create and format Web page without having to learn HTML programming first.
  Regardless of which page appears when you first start Internet Explorer--the Microsoft network home page, your university’s home page, or a different home page--your window should share some common components with the one in Figure 6-5[5].

Explorer Window Fig. 6-5 Internet
  这一段有两处需要解释
  ① Which Internet……on your computer[4] ,这一句中your computer …为定语从句,修饰tool ,谓语depends on 后面跟的how Internet…… 是宾语从句
  ② Regardless of…… 这一长句中,由一对波折号内的是同位语,是对Regardless of which page appears 的补充说明。主句是your window should share……,句中with the one 系指微软的MSN主页
  ◆ Paragraph 3 : About the search engine
  第3段 : 关于搜索因亲引擎
  3. Search Engines
  Today there is quite a collection of search tools available that allows us to find information on the Web quickly and easily. The collection of search tools is constantly evolving, with new ones coming on the scene and others disappearing. Rather than report on how each of the popular search tools works, we will explain a few of them and suggest some Web presentations that provide reviews of all of the current search tools available. [6]
  (1)Yahoo
  Yahoo! search enables you to find exactly what you're looking for,   faster and easier than ever.
  Use it and enjoy the following:
  Relevant, comprehensive results
  Clean, easy to use interface
  Search start page
  Image search
  Customizable preferences [7]
  Timesaving shortcuts for news, yellow pages and maps
Whatever you're looking for, Yahoo! search is the shortcut to what you want..
   (2)Google
   You know a site has the right stuff when its name becomes a verb. In just three years, Google has evolved from a nascent Net presence into a daily destination for millions who use it for fast answers from the Net[8]. Even Yahoo! uses it, providing Google results to augment[9] its own directory.
  But Google is much more than just a tool for finding sites, and most Web surfers barely scratch the surface of its capabilities[10]. If you know what you're doing, Google can help you accomplish everything from looking up phone numbers to tracking down images.
  这一段有3个句子需要解释:
  ① Rather than引导的是为方式状语从句,在这一长句中,report为名词,on how 后面为介词宾语从句。主句中 that 引导的是定语从句,修饰Web presentations
  ② You know a site…… 这一句中, stuff 是俚语,表示本领、能力
  ③ In just three years, Google…… 句中evolved from……into…… 为从……发展成为……。Net为网络,Net presence 可译为上网的工具,句中后面的the Net 也是指这一网络工具。who 引导的是定语从句

  NOTES
  [1] framework框架,此处理解为工作机制、工作模式。
  [2] 此处说明两种指定URL的方法,后者用链接(Link)或用超链接(Hyperlink)方式。
  [3] Web浏览器将最后一次访问Web服务器的地址和目录作为未给出服务器的访问。
  [4] 从句which…has作为主语,depends为谓语,how …为宾语从句。
  [5] 长句。中间用波折号隔开的是同位语,主句是your windows….是指微软网络主页。
  [6] rather than引导方式状语从句,表示“而不是…”,how引导的从句作宾语;that引导的定语从句修饰presentations,that在从句中做主语。
  [7] customizable相当于custom-made,表示“可定制的”。
  [8] evolve 逐步形成,发展,进化,成长。evolve from … to … 从…发展成为…,who 引导的定语从句修饰millions.
  [9] augment 扩大,增加, 加强, 提高.
  [10] scratch 动词,原意为抓,刻写,scratch the surface 为肤浅的了解,探讨.

  Ⅳ. Summary :
  Describe the basic architecture of WWW and how to use Web, especially introduce the famous browser—MS—Internet Explorer (IE) and the most famous search engines—Yahoo! And Google.
  小结:本节叙述了万维网的基本结构和如何使用万维网,重点介绍了最著名的浏览器—微软公司的因特网浏览器(IE)和最著名的搜索引擎—雅虎和谷歌。

  Ⅴ. Exercises
  Fill in the blanks with appropriate words or phrases.
  1. The World Wide Web is also called as ( )or( )
  2. Each client computer in the WWW uses ( )
  3. Each server in the WWW needs ( )
  4. The abbreviation of the Internet Uniform Resource Locator is ( )
  5. The URL specifies the ( )of the Web server, the directory and name of the specific page wanted.
  6. The Web browser and Web server must use the same standard( )in order to perform the Web functions.
  7. HTML stands for ( )
  8. A Web browser introduced by Microsoft is ( )
  9.( )software has the functions of both E-mail and newsgroup manager
  10. Using the tool of the Windows Media Player we can( )
  11. There are two famous search engines in this text, they are( )and
  12. With Google we can accomplish everything from( ) to( )

6-4 ELECTRONIC MAIL
第4节 电子邮件

  Ⅰ. Objectives :
  Understand the architecture of E-mail, introduce some important protocol standards used for E-mail
  本节的主要目标是:
  了解电子邮件的结构,概述一些用于电子邮件的协议标准
  学习主要词汇:

  Ⅱ. Key words :
  Electronic mail (e-mail)    电子邮件
  message    电文
  agent    代理
  Simple Mail Transfer Protocol (SMTP)   简单邮件传送协议
  Multipurpose Internet Mail Extension (MIME)    多用途网间邮件传送协议
  Post Office Protocol (POP)    邮电局协议

  Ⅲ.Reading and comprehension
  课文重点内容的阅读和理解
  Electronic mail (or E-mail) was one of the earliest applications on the Internet and is still among the most heavily used today. With E-mail, users create and send messages to one user, several users, or all users on a distribution list. Most E-mail software enables users to send text messages and attach files from word processors, spreadsheets, or graphics programs[1].
  1. E-mail Standards
  Several standards have been developed to ensure compatibility between different E-mail software packages. There are three E-mail standards in the same basic fashion. Fig.6-6 shows how an E-mail message can travel over a wide area network such as the Internet.

Fig.6-6 E-mail clients and servers.
  Each client computer in the local area network runs an application layer software package called a user agent. Eudora, Lotus cc:Mail, and Microsoft Mail are all E-mail software packages. The user writes the E-mail message using one of these user agents, which formats the message into two parts:
  ●The header, which lists source and destination E-mail addresses (possibly in text form ,e.g., "Pat Smith") as well as the address itself (e.g., psmith@somewhere.com), date, subject, and so on
  ●The body, which is the message itself
  The user agent sends the message (header and body) to a mail server that runs a special application layer software package called a message transfer agent. These agents read the envelope[2] and then send the message through the network (possibly through dozens of message transfer agents) until the message arrives at the receiver's mail server. The message transfer agent on this server then stores the message in the receiver's mailbox on the server.
  When the receiver next accesses his or her E-mail, the user agent on the receiver's client computer contacts the message transfer agent on the mail server and asks for the contents of the user's mailbox. The message transfer agent sends the E-mail message to the client computer, which the user reads with the user agent.
   The Simple Mail Transfer Protocol (SMTP) is one of the most commonly used e-mail standards. As the name suggests, SMTP is a simple standard that permits only the transfer to text messages; no non-text files such as graphics or word-processing documents are permitted. Several standards for non-text files have been developed that can operate together with SMTP, such as Multipurpose Internet Mail Extension (MIME).
  Fig.6-7 shows a simple E-mail message formatted using SMTP.
  The header of an SMTP message has a series of fields that provide specific information, such as the sender's e-mail address, the receiver's address, date, and so on. The information in quotes on the to and from lines is ignored by SMTP; and only the information in the angle brackets is used as the E-mail address. The message body contains the actual text of the message itself, and must begin with the word DATA.
  
  Fig.6-7 An example of an E-mail message using the SMTP standard.
  The SMTP standard covers message transmission between message transfer agents (i.e., mail server to mail server). A different standard called Post Office Protocol (POP) defines how user agents operate and how messages to and from mail transfer agents are formatted.
  2. E-mail Directories[3]
  Before you can send an E-mail message, you must know the receiver's E-mail address. Many organizations provide E-mail directories on their Web sites. Other E-mail addresses are well known. For example, the E-mail address of the president of the United States is president@whitehouse.gov.
  本节课文中无疑难句,仅有两个长句需稍做解释
  ① As the name suggests…… 长句由 As 引导的是方式状语从句, that 引导的是定语从句,such as 后面是同位语
  ② Several standards for…… 这句话中,that 引导的是定语从句,修饰相隔较远的standards ,such as 引导是同位语
  
  NOTES
  [1] 此处系指用其它软件工具,如MS Word做成的文件可以作为电子邮件的附件。
  [2] 此处比喻为邮政中的信封,实为邮件的头部信息。
  [3] Directories目录,电话号码簿,此处是指电子邮件地址。
  Ⅳ. Summary :
  This section describes the basics of E-mail, which concerns E-mail transfer procedure, E-mail message format and so forth.
  小结:本节叙述了电子邮件的基础知识,涉及到电子邮件传送过程,邮件的报文格式等

  Ⅴ. Exercises
  True/false
  1.( ) E-mail is one of the latest applications on the Internet.
  2.( ) With e-mail we can send messages to all users on a distribution list.
  3.( )Most of e-mail software enable users to send text messages with attach files.
  4.( ) In the e-mail a user needs a message transfer agent.
  5.( )The message itself sent by user is called the body.
  6.( )User reads his or her e-mail message with the user agent.
  7.( )Every user in the e-mail system has a mailbox on the client computer.
  8.( )SMTP can be used to transfer non-text files.
  9.( )When you send an e-mail you should provide the sender’s e-mail address.
  10.( )The SMTP standard defines how user agents operate.
  11.( )The POP defines how messages to and from mail transfer agents are formatted.
  12.( )Many organizations provide e-mail directories on their Web sites

6-5 NETWORK SECURITY
第5节 网络安全

  Ⅰ. Objectives :
  Understand some issues concerning the security of computer network, they are network viruses, unauthorized access and network firewall.
  本节的主要目标是:
  了解有关计算机网络安全的几个问题,它们是网络病毒,非授权访问和网络防火墙.
  学习主要词汇:
  Ⅱ. Key words :
  network security    网络安全
  virus    病毒
  unauthorized access    非授权访问
  firewall    防火墙
  boot    自举,引导,启动
  sector    (磁盘)扇区,扇面
  macro virus    宏病毒
  floppy disk    软(磁)盘
  download    下载,卸载
  identification    识别,验证,鉴定
  authentication    验证,鉴别
  password    口令,密码
  access card    存取卡
  biometric device    生物统计仪器
  filter    过滤,滤波
  block    封锁
  NFS(Network File System)    网络文件系统
  gateway    网关
  relay service    中继业务
  packet filtering    分组(包)过滤
  circuit gateway    电路网关
  application-level gateway    应用级网关
  screening router    屏蔽路由器
  bastion host    堡垒主机
  dual-homed gateway    双宿主网关
  screened-host gateway    屏蔽主机网关
  screened subnet    屏蔽子网
  Ⅲ.Reading and comprehension
  课文重点内容的阅读和理解
  ◆ Paragraph 1 : Introduction   So far in this chapter we’ve looked at the benefits and possibilities that computer networks provide. Unfortunately, there is also a dark side to this rosy picture. Because of the prolific nature of computers and networks today, an opportunity exists for criminals to commit acts that are not in the public interest. Such acts run the gamut from stealing money to intentionally destroying corporate data to stalking children over the Internet. Three issues that are very important with regards to network security—computer viruses, unauthorized access, and firewall—are discussed next.
  第1段:概述
  这一段请注意Because of the prolific…… 这句话,Because of 引导的是原因状语,主句为an opportunity exists…… ,to commit acts 为目的状语,that 引导的是定语从句,修饰acts
  ◆ Paragraph 2 : About network viruses
  1.Network Viruses
  (1)What Are Viruses?
  A virus-----or more formally, a computer virus, is a computer program that is able to make a copy of itself without you knowing what is happening. A virus may copy itself from one part of your hard disk to another, or it may copy itself from one computer to another.
  Most viruses do more than[1] make copies of themselves. Some of them cause real damage, say, by deleting files on your hard disk. Others are merely annoying. They may display a message on your monitor or cause something strange to happen as you are working. All viruses are malevolent in that they do their work without your knowing what is happening, and they can cause problems merely by spreading uncontrollably.
  (2)Types of Viruses
  Although thousands of viruses roam machines and networks all over the world, most have common traits that can be categorized into one of the following groups[2]:
  ● Boot sector viruses
  ● File infector viruses
  ● Macro viruses
  (3)How Do You Get a Virus?
  Most viruses today are transmitted through the Internet. The macro virus is the fastest spreading virus because it is usually transferred from machine to machine via E-mail attachments. However, viruses can also be transmitted through floppy disks, file transfers, and Web downloads. In addition, macro viruses infect all open files of a specific application.
  Therefore, if your machine has a Microsoft Word macro virus, it will infect all Word documents that are open on your machine. If you save those infected files to a floppy disk, you will transfer the infection along with the file when you copy it to another hard drive, or open it on another machine using the same application[3].
  In addition, using the Web to download files is another common way to get a virus. Sites that allow users to share information over the Internet, such as Napster and Gnutella, are a potential breeding ground for computer viruses, much like real-world viruses breed in high traffic areas such as malls and schools.
  第2段:关于网络病毒
  这一段有3个句子需要解释:
  ① All viruses are malevolent in that they…… 句中,in that 引导的是原因状语从句,without 引导的是条件状语从句,what 引导的是宾语从句。
  ② If you save those…… 这一长句中,If 引导的是条件状语从句,along with……为介词短语,when you copy…… 为时间状语从句,using the…… 为定语,修饰machine 。
  ③ Sites that allow……这一长句中,,主句为Sites……are…… ,其中that allow 为定语从句,修饰Sites ,such as Napster…… 为同位语,much like 引导的为方式状语。
  ◆ Paragraph 3 : About unauthorized access
  2. Unauthorized Access
  Unauthorized access—the use of a computer, network, or network resource without permission, is a very important network security issue. To prevent unauthorized access, some type of identification procedure must be used. These vary from passwords to physical access objects (keys, access cards, etc.) to biometric devices that verify some type of personal characteristic, such as a fingerprint.[4]
  Some of the most secure access control systems address both identification and authentication. Identification involves verifying that the person’s name or other identifying feature is listed as an authorized user, and authentication refers to determining whether or not the person is actually who he or she claims to be.[5]
  第3段:关于非授权访问
  本段有两句话需要解释
  ① These vary from…… 这一句中,biometric devices由that 引导的定语从句修饰,括号中的keys 实际上是加密 / 解密的密钥
  ② Identification involves……这一句是并列句,前一句中动名词verifying 作宾语,后面that 引导的是宾语从句;后一句中to determining 为介词宾语。最后的he or she…… 为定语从句,修饰前面的who
  ◆Paragraph 4 : About firewall
  3. Firewalls
  The purpose of a network firewall is to provide a shell around the network, which will protect the systems connected to the network from various threats.
  A firewall can reduce risks to network systems by filtering out inherently insecure network services. Network File System (NFS) services, for example, could be prevented from being used from outside of a network by blocking all NFS traffic to or from the network. This protects the individual hosts while still allowing the service, which is useful in a LAN environment, on the internal network. Instead what is needed is a way to filter access to the network while still allowing users access to the "outside world". A typical network firewall can be depicted as shown in Fig.6-8
   In this configuration, the internal network is separated from external networks by a firewall gateway. A gateway is normally used to perform relay services between two networks[6]. In the case of a firewall gateway, it also provides a filtering service which limits the types of information that can be passed to or from hosts located on the internal network{7}. There are three basic techniques used for firewalls: packet filtering, circuit gateway, and application gateways. Often, more than one of these is used to provide the complete firewall service.
  There are several configuration schemes of firewall in the practical application of inter-network security. They usually use the following terminologies:

Fig. 6-8 Typical network firewall configuration
  ● Screening router -- it can be a commercial router or a host--based router with some kind of packet filtering capability.
  ● Bastion host -- it is a system identified by the firewall administrator as a critical strong point in the network security.
  ● Dual--homed gateway -- some firewalls are implemented without a screening router, by placing a system on both the private network and the Internet, and disabling TCP/IP forwarding.
  ● Screened--host gateway -- it is possibly the most common firewall configuration. This is implemented using a screening router and a bastion host.
  ● Screened subnet -- an isolated subnet is situated between the Internet and the private network. Typically, this network is isolated using screening routers, which may implement varying levels of filtering.
  ● Application-- level gateway -- it is also called a proxy gateway and usually operates at a user level rather than the lower protocol level common to the other firewall techniques.
  第4段:关于防火墙
  这一段有两句话需要解释:
  ① Instead what is…… 这句话中,Instead 为副词,原意为代替、更换、而不是之意,往往与前一句所说的相反,但本文在摘编时将前一句话删去了,故此处Instead 可不译,直接从what is needed 这一主语从句开始翻译。
  ② In the case of……这句话中,有which 和 that 两个关系代词引导的定语从句,分别修饰a filtering service 和 information

  NOTES
  [1] more than 在这里表示“不只…,不仅仅…”。
  [2] although 引导让步状语从句;that引导定语从句修饰common traits;categorize 使列入...的范畴;将...分类。
  [3] If you…是表示条件的状语从句;along with…为介词短语,表示伴随,意为“连同...一起, 随同...一起”;when you copy….为时间状语从句;using the….是现在分词短语作定语后置修饰machine。
  [4] physical access object, 物理访问对象,实际是指具体的安全控制措施.如加密(书中keys应为加/解密的密钥).句中biometric devices 后面由that 引导的定语从句修饰.
  [5]并列句,句中有动名词作宾语 (verifying) 或介词宾语 (to determining) .而最后 he or she claims to be 为定语从句修饰前面的 who。claim 声称,请求,此处是指验证该人是否已经向系统注册。
  [6] gateway 网关,系指现在比较通行称呼的路由器.
  [7] 句中由 which 和that 两个关系代词引导的定语从句,分别修饰a filtering service 和information.

  Ⅳ. Summary :
  This article describes some problems of security of computer networks
  小结:本节叙述了计算机网络安全的一些问题
  Fill in the blanks with appropriate terms or phrases.
  1. There is a ( )in the rosy picture of the Internet
  2. Three very important issues concerned with network security are ( ) , ( ) and ( )
  3. A virus may copy itself from one computer to ( )
  4. Some viruses cause real damage by ( )
  5. All viruses are ( ) in that they do their work without your knowing what is happening
  6.Generally, we can categorize the viruses into one of the following groups: ( ), ( )and ( )viruses
  7. ( ) is usually transferred from computer to computer via E-mail attachments
  8. Sites allowing users to share information over the Internet are ( )
  9.Unauthorized access means that users access a computer, network or network resource without( )
  10.We can protect the unauthorized access by using( ), ( ) and ( )
  11. Some of the most secure access control systems address both( ) and( )
  12.The purpose of a network firewall is to protect the systems connected to the network from( )
  13.A firewall gateway is used to separate the internal network from ( )
  14.There are three basic techniques used for firewall, they are ( )
  15.A system that identified by the firewall administrator as a critical strong point in the network security is ( )
  16. A firewall implemented by a screening router and bastion host is called ( )
  17.A system that places on both the private network and the Internet and blocks TCP/IP forwarding is ( )
  18.An isolated subnet that is situated between the Internet and the private network is( )

6-6 ABOUT INTERNET 2
第6节 关于因特网2

  Ⅰ. Objectives :
  Understand the overview of being developed the Internet 2
  本节的主要目标是:
  了解正在开发的因特网2的概况
  学习主要词汇:

  Ⅱ. Key words :
  virtual laboratory    虚拟实验室
  digital library     数字图书馆
  multicasting     多播,组播
  Quality of Service (QoS)     服务质量

  Ⅲ.Reading and comprehension
  课文重点内容的阅读和理解
  ◆ Paragraph 1 : What is Internet 2
  1.What is Internet 2?   Internet 2 is a not-for-profit consortium, led by over 180 USA universities, developing and deploying advanced network applications and technologies, accelerating the creation of tomorrow’s Internet. With participation by over 60 leading companies, Internet 2 recreates the partnership of academia, industry and government that helped foster today’s Internet in its infancy.
  第1段:什么是Internet2 ?
  这一段请注意Internet2 recreates……这句话中 With 引导的是方式状语,that 引导的定语从句修饰相隔较远的partnership 的
  ◆ Paragraph 2 : The relationship between Internet 2 and the current Internet
  2. Is Internet 2 a separate network? Will Internet 2 replace the current commercial Internet?
  Internet 2 is not a separate physical network and will not replace the Internet. Internet 2 brings together institutions and resources from academia, industry and government to develop new technologies and capabilities that can then be deployed in the global Internet. Close collaboration with Internet 2 corporate members will ensure that new applications and technologies are rapidly deployed throughout the Internet. Just as E-mail and the World Wide Web are legacies of earlier investments in academic and federal research networks, the legacy of Internet 2 will be to expand the possibilities of the broader Internet.
  第2段:因特网2与现在的因特网之间的关系
  这一段请注意最后一句话Just as E-mail…… 中Just as 引导的是方式状语从句,主句是the legacy of Internet 2……
  ◆ Paragraph 3 : Benefits of Internet 2
  3. How will Internet 2 benefit current Internet users?
  Internet 2 and its members are developing and testing new technologies, such as Ipv6, multicasting, and QoS.[1] However, these applications require performance not possible on today’s Internet. More than a faster Web or E-mail, these new technologies will enable completely new applications such as digital libraries, virtual laboratories, distance-independent learning and tele-immersion[2].A primary goal of Internet 2 is to ensure the transfer of new network technologies and applications to the broader education and networking communities.
  第3段:因特网2带来的好处
  这一段请注意More than a faster…… 这一句话中,such as 引导的是同位语
  ◆ Paragraph 4 : The relationship among the NGI, Internet 2 and other advanced networks
  4. What is the relationship between the Next Generation Internet (NGI) Internet 2, and other advanced networking initiatives?
  The university-led Internet 2 and the federally-led NGI are parallel and complementary initiatives based in the United States. Internet 2 and NGI are already working together in many areas. For example, through participation in a NSF NGI program, over 150 Internet 2 universities have received competitively awarded grants to support connections to advanced backbone networks such as Abilene and the very high performance Backbone Network service (vBNS) [3]. Internet 2 is also forming partnerships with similar advanced networking initiatives around the world. Working together will help ensure a cohesive and interoperable advanced networking infrastructure for research and education, and the continued interoperability of the global Internet.
  第4段:下一代因特网,因特网2和其它先进网络之间的关系
  这一段中注意initiatives 这一词的用法,其原意是主动权,首创精神,此处可译为先进技术
  ◆ Paragraph 5 : Long-term goals of Internet 2
  5. What are some of Internet 2’s long-term goals?
  A key goal of this efforts is to accelerate the diffusion of advanced Internet technology, in particular into the commercial sector. In this way, Internet 2 will help to sustain United States leadership in internetworking technology. Internet 2 will benefit non-university members of the educational community as well, especially k-12 and public libraries. Internet 2 and its members aim to share their expertise with as wide a range of computer users as possible. This approach characterized the first Internet and it can work again today. For Internet 2 universities, this means providing high-performance networking on their campuses-investing to upgrade their campus networks and connecting to a national Internet 2 backbone network. For Internet 2 corporate partners, this means actively collaborating with Internet 2 universities and in Internet 2 initiatives.

  NOTES
  [1] Ipv6,互联网协议第6版 (version 6) ,其主要的改进在IP编址上,改为128位IP地址方式,以解决目前Ipv4 32位地址所造成的地址资源不足的问题;multicasting指多播; QoS是 Quality of Service的缩写,指服务质量。
  [2] tele-immersion,此处应理解为远程登录。
  [3] NSF (National Science Foundation),(美)国家科学基金会。Abilene是Internet高性能主干网,是为参与Internet 2的大学和科研实验室开发先进的Internet应用和布置高级服务提供全国性支持的网络
  [4]k-12的英文全称是Kindergarten to 12th grade,为幼儿园到12年级(相当于我国高中三年级)

  Ⅳ. Summary :
  This section describes the Internet 2, including its goals, new initiatives used, benefits to be obtained and the relationship between Internet 2 and others.
  小结:本节叙述因特网2,包括它的目标,所采用的新技术,将要获得的好处,以及与其它网络之间的关系。

  Ⅴ. Exercises
  True/False.
  (1)( )Internet 2 will replace the current commercial Internet.
  (2) ( )The Next Generation Internet is federally-led.
  (3) ( )Internet 2 is a not-for-profit consortium.
  (4) ( )Internet 2 is a separate physical network.
  (5) ( )Most PC machines sold today include the ability to use the Internet.
  (6) ( )Ipv6 has 128-bit address mode.
  (7) ( )Internet 2 will benefit university members only.
  (8) ( ) Internet 2 will become a backbone network of U.S.A
  (9) ( ) Over 60 leading companies have participated in the Internet 2.
  (10)( )Less than 180 Internet 2 universities have received competitively awarded grants to support connections to advanced backbone networks.