第8章 計算機專業(yè)英語 孫建忠

1、Chapter 8 The Internet 計算機專業(yè)英語計算機專業(yè)英語8-1Computer EnglishChapter 8 The Internet: Technology Background Chapter 8 The Internet 8-2 了解了解Internet的起源的起源 掌握掌握Internet的關(guān)鍵技術(shù)概念的關(guān)鍵技術(shù)概念 描述描述 Internet協(xié)議與應用程序的作用協(xié)議與應用程序的作用 解釋當前解釋當前Internet的結(jié)構(gòu)的結(jié)構(gòu) 理解當前理解當前Internet的局限的局限 描述描述Internet II的潛在作用的潛在作用 掌握英語長句的翻譯技巧掌握英語長句的翻

2、譯技巧Requirements:Chapter 8 The Internet 8-38.1 The Internet: Technology Background New Words & Expressionshyperlink n.計計超鏈接超鏈接pundit n. 空談家空談家, 權(quán)威性的評論者權(quán)威性的評論者glibly adv.流利地流利地, 流暢地流暢地conceptualize v.使有概念使有概念legitimization n.合法化合法化, 認為正當認為正當institutional adj.制度上的制度上的,機構(gòu)上的機構(gòu)上的fledging n.剛會飛的幼鳥剛會飛的幼

3、鳥,無經(jīng)驗的人無經(jīng)驗的人follow-on 繼續(xù)繼續(xù)slice vt.把把.切成薄片切成薄片; 把把.分成部分分成部分break down 破壞；拆散細分；分類破壞；拆散細分；分類disabled n.禁止使用的禁止使用的quad n. 四元組四元組mainframe n.計計主機主機, 大型機大型機vulnerable adj.易受攻擊的易受攻擊的, gigabyte n.十億字節(jié)十億字節(jié)(giga-為字首為字首,“十億十億”) supercomputer n.計計 超型計算機超型計算機reminiscent adj. 懷舊的；回憶的懷舊的；回憶的Domain Name 域名域名host c

4、omputer (host) 主機主機instant messaging 即時信息服務(wù)即時信息服務(wù)packet-switching 分組交換技術(shù)分組交換技術(shù)client/server 客戶機客戶機/服務(wù)器服務(wù)器circuit switching 線路轉(zhuǎn)接線路轉(zhuǎn)接bit n.計計位位, 比特比特Router 計計 路由器路由器routing algorithm 路徑算法路徑算法Ethernet n.以太網(wǎng)以太網(wǎng)token ring networks 令牌環(huán)形網(wǎng)令牌環(huán)形網(wǎng)Telnet 遠程登錄遠程登錄Finger 查找因特網(wǎng)用戶的程序查找因特網(wǎng)用戶的程序Ping 測試測試IP地址的程序地址的程序T

5、racert 檢查路由器程序檢查路由器程序UNIX 美國美國AT&T公司的操作系統(tǒng)公司的操作系統(tǒng), UNIX操作系統(tǒng)操作系統(tǒng)let alone 更不用說更不用說Chapter 8 The Internet 8-4AbbreviationsTCP (Transfer Control Protocol) 傳輸控制協(xié)議傳輸控制協(xié)議IP(Internet Protocol) 網(wǎng)際協(xié)議網(wǎng)際協(xié)議FTP (File Transfer Protocol) 文件傳輸協(xié)議文件傳輸協(xié)議POP (Post Office Protocol)郵局協(xié)議郵局協(xié)議HTTP(Hypertext Transfer Prot

6、ocol)超文本傳輸協(xié)議超文本傳輸協(xié)議IP address IP地址地址URL (Uniform Resource Locator) 統(tǒng)一資源定位統(tǒng)一資源定位DNS (domain name system) 域名系統(tǒng)域名系統(tǒng)SSL (Security Socket Layer) 加密套接字協(xié)議層加密套接字協(xié)議層RAM (random access memory) 隨機存儲器隨機存儲器ARPANET (Advanced Research Projects Agency Network) 美國國防部高級研美國國防部高級研究計劃局建立的計算機網(wǎng)究計劃局建立的計算機網(wǎng)ICANN (Internet C

7、orporation for Assigned Names and Numbers) 因特網(wǎng)域名與因特網(wǎng)域名與地址管理組織地址管理組織 SMTP (Simple Message Transfer Protocol)簡單郵件傳輸協(xié)議簡單郵件傳輸協(xié)議, 用于電子郵件的傳用于電子郵件的傳輸輸IMAP (Internet Message Access Protocol) Internet消息訪問協(xié)議消息訪問協(xié)議Chapter 8 The Internet 8-5What is the Internet? Where did it come from, and how did it support th

8、e growth of the World Wide Web? What are the Internets most important operating principles? The Internet is an interconnected network of thousands of networks and millions of computers (sometimes called host computers or just hosts) linking businesses, educational institutions, government agencies,

9、and individuals together. The Internet provides around 400 million people around the world (and over 170 million people in the United States) with services such as e-mail, newsgroups, shopping, research, instant messaging, music, videos, and news. No one organization controls the Internet or how it

10、functions, nor is it owned by anybody, yet it has provided the infrastructure for a transformation in commerce, scientific research, and culture. 因特網(wǎng)是什么因特網(wǎng)是什么? 它來自何處，和它如何支持萬維網(wǎng)的增長它來自何處，和它如何支持萬維網(wǎng)的增長? 因特網(wǎng)最重要的運行原則是因特網(wǎng)最重要的運行原則是什么什么?因特網(wǎng)是成千上萬的網(wǎng)絡(luò)和數(shù)以百萬計的計算機因特網(wǎng)是成千上萬的網(wǎng)絡(luò)和數(shù)以百萬計的計算機(有時被稱為主機計算機或主機有時被稱為主機計算機或主機)將企業(yè)

11、、教育機構(gòu)、政府機關(guān)和個人聯(lián)結(jié)起來的一個互聯(lián)網(wǎng)絡(luò)。因特網(wǎng)為全球大約將企業(yè)、教育機構(gòu)、政府機關(guān)和個人聯(lián)結(jié)起來的一個互聯(lián)網(wǎng)絡(luò)。因特網(wǎng)為全球大約4億億人人(其中美國其中美國1.7億多人億多人)提供諸如電子郵件、新聞討論組、購物、研究、即時信息、音提供諸如電子郵件、新聞討論組、購物、研究、即時信息、音樂、視頻和新聞等服務(wù)。沒有任何組織控制因特網(wǎng)或它的運作樂、視頻和新聞等服務(wù)。沒有任何組織控制因特網(wǎng)或它的運作,它也不被任何人所擁有它也不被任何人所擁有,盡管它為商業(yè)交易、科學研究和文化提供基礎(chǔ)設(shè)施。盡管它為商業(yè)交易、科學研究和文化提供基礎(chǔ)設(shè)施。Chapter 8 The Internet 8-6The w

12、ord Internet is derived from the word internetwork or the connecting together of two or more computer networks. The World Wide Web, or Web for short, is one of the Internets most popular services, providing access to over one billion Web pages, which are documents created in a programming language c

13、alled HTML and which can contain text, graphics, audio, video, and other objects, as well as “hyperlinks” that permit a user to jump easily from one page to another. 因特網(wǎng)因特網(wǎng)(Internet)一詞起源于互聯(lián)網(wǎng)絡(luò)一詞起源于互聯(lián)網(wǎng)絡(luò)(internetwork)或兩個或更或兩個或更多的計算機網(wǎng)絡(luò)聯(lián)接在一起。全球信息網(wǎng)多的計算機網(wǎng)絡(luò)聯(lián)接在一起。全球信息網(wǎng),或簡稱萬維網(wǎng)或簡稱萬維網(wǎng),是因特是因特網(wǎng)上最流行的服務(wù)之一網(wǎng)上最流行的服務(wù)之一

14、,提供對提供對10億多網(wǎng)頁的訪問，這些網(wǎng)頁是億多網(wǎng)頁的訪問，這些網(wǎng)頁是由一種叫做由一種叫做HTML(超文本鏈接標示語言超文本鏈接標示語言)編程語言生成的文件，編程語言生成的文件，它可以包含本文、圖形、聲頻、視頻和其他對象、以及允許用戶它可以包含本文、圖形、聲頻、視頻和其他對象、以及允許用戶容易地跳躍到其他網(wǎng)頁的容易地跳躍到其他網(wǎng)頁的“超鏈接超鏈接”。Chapter 8 The Internet 8-78.1.1 THE EVOLUTION OF THE INTERNET 19612000 Internet Itodays Internethas evolved over the last fo

15、rty years. In this sense, the Internet is not “new”; it did not happen yesterday. Although journalists and pundits talk glibly about “Internet” timesuggesting a fast-paced, nearly instant, worldwide global change mechanism, in fact, it has taken forty years of hard work to arrive at todays Internet.

16、因特網(wǎng)因特網(wǎng)I今天的因特網(wǎng)今天的因特網(wǎng)已經(jīng)發(fā)展了四十多年。在這個意義上，因特網(wǎng)不是已經(jīng)發(fā)展了四十多年。在這個意義上，因特網(wǎng)不是“新的新的”,它不是昨天才發(fā)生的事。雖然新聞記者和博學家口若懸河地談?wù)撍皇亲蛱觳虐l(fā)生的事。雖然新聞記者和博學家口若懸河地談?wù)摗耙蛱匾蛱鼐W(wǎng)網(wǎng)”時代時代指一種快步調(diào)的、幾乎即時的、全球性的變化機制，事實上，因特網(wǎng)指一種快步調(diào)的、幾乎即時的、全球性的變化機制，事實上，因特網(wǎng)達到今天的水平花費了四十年的艱苦努力。達到今天的水平花費了四十年的艱苦努力。Chapter 8 The Internet 8-8The history of the Internet can be seg

17、mented into three phases. In the first phase, the Innovation Phase, from 1961 to 1974, the fundamental building blocks of the Internet were conceptualized and then realized in actual hardware and software. The basic building blocks are: packet-switching hardware, client/server computing, and a commu

18、nications protocol called TCP/IP (all described more fully below). The original purpose of the Internet, when it was conceived in the late 1960s, was to link together large mainframe computers on college campuses. This kind of one-to-one communication between campuses was previously only possible th

19、rough the telephone system or postal mail. 因特網(wǎng)的歷史可以劃分為三個階段。在第一階段即發(fā)明階段，從因特網(wǎng)的歷史可以劃分為三個階段。在第一階段即發(fā)明階段，從1961年到年到1974年，因特網(wǎng)的基本構(gòu)建模塊被概念化并隨之用真正的硬件和軟件實現(xiàn)。年，因特網(wǎng)的基本構(gòu)建模塊被概念化并隨之用真正的硬件和軟件實現(xiàn)。其基本的構(gòu)建模塊是其基本的構(gòu)建模塊是:分組交換硬件、客戶機分組交換硬件、客戶機/服務(wù)器計算技術(shù)和一個被稱服務(wù)器計算技術(shù)和一個被稱為傳輸控制協(xié)議的通信協(xié)議為傳輸控制協(xié)議的通信協(xié)議(它們都將在后文進行全面描述它們都將在后文進行全面描述)。當在當在20世紀世紀

20、60年代末期構(gòu)思的時候，因特網(wǎng)最初的目的是將大學校園內(nèi)的大型計算機年代末期構(gòu)思的時候，因特網(wǎng)最初的目的是將大學校園內(nèi)的大型計算機聯(lián)結(jié)起來。在校園之間這種一對一的通信先前只有經(jīng)過電話系統(tǒng)或郵政郵聯(lián)結(jié)起來。在校園之間這種一對一的通信先前只有經(jīng)過電話系統(tǒng)或郵政郵件才可能進行。件才可能進行。 8.1.1 THE EVOLUTION OF THE INTERNET 19612000 Chapter 8 The Internet 8-9In the second phase, the Institutional Phase, from 1975 to 1995, large institutions su

21、ch as the Department of Defense and the National Science Foundation provided funding and legitimization for the fledging invention called the Internet. Once the concept of the Internet had been proven in several government-supported demonstration projects, the Department of Defense contributed a mil

22、lion dollars to develop the concepts and demonstration projects into a robust military communications system that could withstand nuclear war. This effort created what was then called ARPANET (Advanced Research Projects Agency Network). In 1986, the National Science Foundation assumed responsibility

23、 for the development of a civilian Internet (then called NSFNet) and began a ten-year-long $200 million expansion program.在第二階段即機構(gòu)化階段在第二階段即機構(gòu)化階段,從從1975年到年到1995年，像國防部和國家科學基金委等一些年，像國防部和國家科學基金委等一些大機構(gòu)為這項被稱為因特網(wǎng)的剛剛起步的發(fā)明提供資金并使其合法化。當因特網(wǎng)的大機構(gòu)為這項被稱為因特網(wǎng)的剛剛起步的發(fā)明提供資金并使其合法化。當因特網(wǎng)的概念在一些政府支持的示范性項目中被證實后，國防部提供了一百萬美元資金將

24、這概念在一些政府支持的示范性項目中被證實后，國防部提供了一百萬美元資金將這個概念和示范性項目發(fā)展成為一個可以承受核戰(zhàn)的軍事通信系統(tǒng)。這個努力產(chǎn)生了個概念和示范性項目發(fā)展成為一個可以承受核戰(zhàn)的軍事通信系統(tǒng)。這個努力產(chǎn)生了以后被稱作以后被稱作ARPANET的東西的東西(高級研究計劃局建立的計算機網(wǎng)高級研究計劃局建立的計算機網(wǎng))。在。在1986年，國家年，國家科學基金委承擔了建立民用因特網(wǎng)的任務(wù)科學基金委承擔了建立民用因特網(wǎng)的任務(wù)(那時叫做那時叫做NSFNet)，并且開始了為期十，并且開始了為期十年、耗資年、耗資2億美元的擴展計劃。億美元的擴展計劃。8.1.1 THE EVOLUTION OF TH

25、E INTERNET 19612000 Chapter 8 The Internet 8-10In the third phase, the Commercialization Phase, from 19952001, government agencies encouraged private corporations to take over and expand both the Internet backbone and local service to ordinary citizensfamilies and individuals across America and the

26、world who were not students on campuses. By 2000, the Internets use had expanded well beyond military installations and research universities. 在第三階段即商業(yè)化階段在第三階段即商業(yè)化階段,從從1995年至年至2001年，政府機構(gòu)鼓勵年，政府機構(gòu)鼓勵私營公司接管并擴展因特網(wǎng)主干和接管為普通市民提供的地方私營公司接管并擴展因特網(wǎng)主干和接管為普通市民提供的地方性服務(wù)，普通市民包括在全美國和全世界的家庭以及非在校學性服務(wù)，普通市民包括在全美國和全世界的家庭以及

27、非在校學生等個體。到生等個體。到2000年，因特網(wǎng)的應用已大大超出了軍事設(shè)備年，因特網(wǎng)的應用已大大超出了軍事設(shè)備和大學研究的范圍。和大學研究的范圍。8.1.1 THE EVOLUTION OF THE INTERNET 19612000 Chapter 8 The Internet 8-118.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS In 1995, the Federal Networking Council (FNC) took the step of passing a resolution formally defining the term

28、 Internet. “Internet” refers to the global information system thatI. is logically linked together by a globally unique address space based on the Internet Protocol (IP) or its subsequent extensions/follow-ons;在在 1995 年，聯(lián)邦的網(wǎng)絡(luò)委員會年，聯(lián)邦的網(wǎng)絡(luò)委員會(FNC)通過了一個關(guān)于因特網(wǎng)術(shù)語正式定義的決議。通過了一個關(guān)于因特網(wǎng)術(shù)語正式定義的決議。“因特網(wǎng)因特網(wǎng)”是這樣的全球信息系統(tǒng)

29、是這樣的全球信息系統(tǒng)I. 通過以因特網(wǎng)協(xié)議或其擴展或繼續(xù)為基礎(chǔ)的、獨特的地址空間被邏輯性通過以因特網(wǎng)協(xié)議或其擴展或繼續(xù)為基礎(chǔ)的、獨特的地址空間被邏輯性地聯(lián)結(jié)起來；地聯(lián)結(jié)起來；Chapter 8 The Internet 8-128.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS II. is able to support communications using the Transmission Control Protocol/Internet Protocol (TCP/IP) suite or its subsequent extensions/fo

30、llow-ons, and/or other IP-compatible protocols; andIII. provides, uses or makes accessible, either publicly or privately, high level services layered on the communications and related infrastructure described herein. II.能夠支持使用能夠支持使用TCP/IP(傳輸控制協(xié)議傳輸控制協(xié)議/因特網(wǎng)協(xié)議因特網(wǎng)協(xié)議)組或其組或其擴展擴展/繼續(xù)、和繼續(xù)、和/或其他與或其他與IP協(xié)議協(xié)議(因特

31、網(wǎng)協(xié)議因特網(wǎng)協(xié)議)兼容的協(xié)議進兼容的協(xié)議進行的通信；并且行的通信；并且III.提供、使用或使可訪問此處描述的通信及其相關(guān)基礎(chǔ)設(shè)提供、使用或使可訪問此處描述的通信及其相關(guān)基礎(chǔ)設(shè)施施(不論公用的還是專用的不論公用的還是專用的)上分層次的高水平服務(wù)。上分層次的高水平服務(wù)。 Chapter 8 The Internet 8-13Based on the definition, the Internet means a network that uses the IP addressing scheme, supports the Transmission Control Protocol (TCP),

32、 and makes services available to users much like a telephone system makes voice and data services available to the public2.基于這個定義，因特網(wǎng)表示這樣一個網(wǎng)絡(luò)基于這個定義，因特網(wǎng)表示這樣一個網(wǎng)絡(luò)使用使用IP地址分配地址分配方案、支持傳輸控制協(xié)議，并使用戶可以使用多種服務(wù)方案、支持傳輸控制協(xié)議，并使用戶可以使用多種服務(wù)與與電話系統(tǒng)使公眾能夠使用聲音和數(shù)據(jù)服務(wù)非常類似。電話系統(tǒng)使公眾能夠使用聲音和數(shù)據(jù)服務(wù)非常類似。8.1.2 THE INTERNET: KEY TECHNOL

33、OGY CONCEPTS Chapter 8 The Internet 8-14Behind this formal definition are three extremely important concepts that are the basis for understanding the Internet: packet switching, the TCP/IP communications protocol, and client/server computing3. Although the Internet has evolved and changed dramatical

34、ly in the last 30 years, these three concepts are at the core of how the Internet functions today and are the foundation for Internet II.在這個正式的定義背后，隱含著三個極其重要的概念在這個正式的定義背后，隱含著三個極其重要的概念:分組交分組交換、換、TCP/IP(傳輸控制協(xié)議傳輸控制協(xié)議/網(wǎng)際協(xié)議網(wǎng)際協(xié)議)通信協(xié)議和客戶機通信協(xié)議和客戶機/服務(wù)服務(wù)器計算技術(shù)，它們乃是理解因特網(wǎng)的基礎(chǔ)。盡管因特網(wǎng)在過去器計算技術(shù)，它們乃是理解因特網(wǎng)的基礎(chǔ)。盡管因特網(wǎng)在過去30

35、年發(fā)生了引人注目的進化和變化，但這三個概念仍是今天因年發(fā)生了引人注目的進化和變化，但這三個概念仍是今天因特網(wǎng)運轉(zhuǎn)的核心，也是因特網(wǎng)特網(wǎng)運轉(zhuǎn)的核心，也是因特網(wǎng)II的基礎(chǔ)。的基礎(chǔ)。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS Chapter 8 The Internet 8-15Packet Switching. Packet switching is a method of slicing digital messages into parcels called “packets,” sending the packets along different

36、 communication paths as they become available, and then reassembling the packets once they arrive at their destination. Prior to the development of packet switching, early computer networks used leased, dedicated telephone circuits to communicate with terminals and other computers. In circuit-switch

37、ed networks such as the telephone system, a complete point-to-point circuit is put together, and then communication can proceed. 分組交換。分組交換是傳輸數(shù)據(jù)的一種方法，它先將數(shù)據(jù)信息分割成許多分組交換。分組交換是傳輸數(shù)據(jù)的一種方法，它先將數(shù)據(jù)信息分割成許多稱為稱為“分組分組”的數(shù)據(jù)信息包；當路徑可用時，經(jīng)過不同的通信路徑發(fā)送；的數(shù)據(jù)信息包；當路徑可用時，經(jīng)過不同的通信路徑發(fā)送；當?shù)竭_目的地后，再將它們組裝起來。在分組交換發(fā)展之前，早期計算機當?shù)竭_目的地后，再將它們組

38、裝起來。在分組交換發(fā)展之前，早期計算機網(wǎng)絡(luò)使用租用的專用電話線路和終端與其他計算機進行通信。在線路交換網(wǎng)絡(luò)使用租用的專用電話線路和終端與其他計算機進行通信。在線路交換網(wǎng)絡(luò)如電話系統(tǒng)中，一個完全點對點的線路被連結(jié)在一起，然后才能進行網(wǎng)絡(luò)如電話系統(tǒng)中，一個完全點對點的線路被連結(jié)在一起，然后才能進行通信。通信。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS Chapter 8 The Internet 8-16However, these “dedicated” circuit-switching techniques were expensive and w

39、asted available communications capacitythe circuit would be maintained regardless of whether any data was being sent. For nearly 70% of the time, a dedicated voice circuit is not being fully used because of pauses between words and delays in assembling the circuit segments, both of which increased t

40、he length of time required to find and connect circuits. A better technology was needed.然而，這些然而，這些“專用的專用的”線路交換技術(shù)既價格昂貴又浪費有效的通信能力線路交換技術(shù)既價格昂貴又浪費有效的通信能力不論是否有數(shù)據(jù)輸送都需要維持線路。由于字間的停頓和組裝時的延遲，不論是否有數(shù)據(jù)輸送都需要維持線路。由于字間的停頓和組裝時的延遲，一條專用的聲音線路在幾乎一條專用的聲音線路在幾乎70%的時間內(nèi)沒有得到充分利用，而這兩種因的時間內(nèi)沒有得到充分利用，而這兩種因素都增加尋找和連接線路所需的時間長度。因此需要一種

41、比較好的技術(shù)。素都增加尋找和連接線路所需的時間長度。因此需要一種比較好的技術(shù)。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS Chapter 8 The Internet 8-17The first book on packet switching was written by Leonard Kleinrock in 1964, and the technique was further developed by others in the defense research labs of both the United States and Engl

42、and. With packet switching, the communications capacity of a network can be increased by a factor of 100 or more. The communications capacity of a digital network is measured in terms of bits per second. Imagine if the gas mileage of your car went from 15 miles per gallon to 1,500 miles per gallonal

43、l without changing too much of the car! 第一本關(guān)于分組交換的著作是由第一本關(guān)于分組交換的著作是由Leonard Kleinrock于于1964年所著，美國年所著，美國和英國防衛(wèi)研究實驗室的其他研究人員使這項技術(shù)得到進一步發(fā)展。由于和英國防衛(wèi)研究實驗室的其他研究人員使這項技術(shù)得到進一步發(fā)展。由于使用分組交換技術(shù)，網(wǎng)絡(luò)的通信能力提高了使用分組交換技術(shù)，網(wǎng)絡(luò)的通信能力提高了100倍甚至更多。數(shù)字網(wǎng)絡(luò)的倍甚至更多。數(shù)字網(wǎng)絡(luò)的通信能力用每秒位來衡量。想象一下汽車行駛的里程，從每加侖汽油行駛通信能力用每秒位來衡量。想象一下汽車行駛的里程，從每加侖汽油行駛15里提高到

44、每加侖汽油行駛里提高到每加侖汽油行駛1500 里里而汽車沒有太大的改變而汽車沒有太大的改變!8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS Chapter 8 The Internet 8-18In packet-switched networks, messages are first broken down into packets. Appended to each packet are digital codes that indicate a source address (the origination point) and a destin

45、ation address, as well as sequencing information and error control information for the packet. Rather than being sent directly to the destination address, in a packet network, the packets travel from computer to computer until they reach their destination. These computers are called routers. Routers

46、 are special purpose computers that interconnect the thousands of different computer networks that make up the Internet and route packets along to their ultimate destination as they travel4. To ensure that packets take the best available path toward their destination, the routers use computer progra

47、ms called routing algorithms.在分組交換的網(wǎng)絡(luò)中，信息首先被分解為許多信息包。每個信息包附加數(shù)字代碼用在分組交換的網(wǎng)絡(luò)中，信息首先被分解為許多信息包。每個信息包附加數(shù)字代碼用于指示其源地址于指示其源地址(開始點開始點)和目的地地址、以及順序信息和錯誤控制信息。在分組網(wǎng)和目的地地址、以及順序信息和錯誤控制信息。在分組網(wǎng)絡(luò)中，信息包不是直接被送到目的地地址絡(luò)中，信息包不是直接被送到目的地地址,而是在計算機與計算機之間旅行直到它而是在計算機與計算機之間旅行直到它們到達目的地。這些計算機叫做路由器。路由器是一種特殊用途的計算機，它將組們到達目的地。這些計算機叫做路由器。路由

48、器是一種特殊用途的計算機，它將組成因特網(wǎng)的成千上萬個不同計算機網(wǎng)絡(luò)互相聯(lián)接起來，并在信息包旅行時將它們的成因特網(wǎng)的成千上萬個不同計算機網(wǎng)絡(luò)互相聯(lián)接起來，并在信息包旅行時將它們的向終極目的地發(fā)送。路由器使用一種叫做路由算法的計算機程序，以確保信息包取向終極目的地發(fā)送。路由器使用一種叫做路由算法的計算機程序，以確保信息包取通向它們目的地的最佳可用路徑。通向它們目的地的最佳可用路徑。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS Chapter 8 The Internet 8-19Packet switching does not require a ded

49、icated circuit but can make use of any spare capacity that is available on any of several hundred circuits. Packet switching makes nearly full use of almost all available communication lines and capacity. Moreover, if some lines are disabled or too busy, the packets can be sent on any available line

50、 that eventually leads to the destination point. 分組交換不需要一個專用線路，但是可以利用幾百條線路中任分組交換不需要一個專用線路，但是可以利用幾百條線路中任何可用的空閑能力。分組交換幾乎充分利用了所有可用的通信何可用的空閑能力。分組交換幾乎充分利用了所有可用的通信線路和能力。而且，如果一些線路不通或太忙的話線路和能力。而且，如果一些線路不通或太忙的話,信息包能信息包能在任何可用的、最終通向目的地的線路上傳送。在任何可用的、最終通向目的地的線路上傳送。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS Chap

51、ter 8 The Internet 8-20TCP/IP. While packet switching was an enormous advance in communications capacity, there was no universally agreed upon method for breaking up digital messages into packets, routing them to the proper address, and then reassembling them into a coherent message. This was like h

52、aving a system for producing stamps, but no postal system (a series of post offices and a set of addresses).TCP/IP。盡管分組交換是通信能力的一個巨大進步。盡管分組交換是通信能力的一個巨大進步,但對于將但對于將數(shù)字信息分解為信息包、將它們傳輸?shù)竭m當?shù)牡刂窋?shù)字信息分解為信息包、將它們傳輸?shù)竭m當?shù)牡刂? 然后重新然后重新組裝為原來的信息，還沒有一種公認的方法。這就像有了一個組裝為原來的信息，還沒有一種公認的方法。這就像有了一個生產(chǎn)郵票的系統(tǒng)生產(chǎn)郵票的系統(tǒng),而沒有郵政系統(tǒng)而沒有郵政系統(tǒng)(一

53、系列的郵局和一套住址一系列的郵局和一套住址)一一樣。樣。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS Chapter 8 The Internet 8-21TCP/IP answered the problem of what to do with packets on the Internet and how to handle them. TCP refers to the Transmission Control Protocol (TCP). IP refers to the Internet Protocol (IP). A protocol

54、 is a set of rules for formatting, ordering, compressing, and error-checking messages. It may also specify the speed of transmission and means by which devices on the network will indicate they have stopped sending and/or receiving messages. Protocols can be implemented in either hardware or softwar

55、e. TCP/IP is implemented in Web software called server software (described below). TCP is the agreed upon protocol for transmitting data packets over the Web. TCP establishes the connections among sending and receiving Web computers, handles the assembly of packets at the point of transmission, and

56、their reassembly at the receiving end.TCP/IP回答了在因特網(wǎng)上用信息包做什么和如何處理信息包的問題?；卮鹆嗽谝蛱鼐W(wǎng)上用信息包做什么和如何處理信息包的問題。TCP指傳輸指傳輸控制協(xié)議，控制協(xié)議，IP表示網(wǎng)際協(xié)議。協(xié)議是一組用于信息的格式化、次序化、壓縮和檢查表示網(wǎng)際協(xié)議。協(xié)議是一組用于信息的格式化、次序化、壓縮和檢查錯誤的規(guī)則。它也可以限定傳輸速度和網(wǎng)上設(shè)備顯示它們已停止發(fā)送及錯誤的規(guī)則。它也可以限定傳輸速度和網(wǎng)上設(shè)備顯示它們已停止發(fā)送及(或或)接收信接收信息的方法。協(xié)議既可以通過硬件也可通過軟件來實現(xiàn)。息的方法。協(xié)議既可以通過硬件也可通過軟件來實現(xiàn)。T

57、CP/IP(傳輸控制協(xié)議傳輸控制協(xié)議/網(wǎng)際網(wǎng)際協(xié)議協(xié)議)通過被稱為服務(wù)器軟件的網(wǎng)絡(luò)軟件來實現(xiàn)通過被稱為服務(wù)器軟件的網(wǎng)絡(luò)軟件來實現(xiàn)(在下文描述在下文描述)。TCP(傳輸控制協(xié)議傳輸控制協(xié)議)是用來在網(wǎng)上傳輸數(shù)據(jù)的公認協(xié)議。是用來在網(wǎng)上傳輸數(shù)據(jù)的公認協(xié)議。TCP(傳輸控制協(xié)議傳輸控制協(xié)議)在發(fā)送和接收網(wǎng)絡(luò)計算機在發(fā)送和接收網(wǎng)絡(luò)計算機之間建立連接之間建立連接,處理信息包在傳輸點的組裝和在接收端的重新組裝。處理信息包在傳輸點的組裝和在接收端的重新組裝。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS Chapter 8 The Internet 8-22TCP/I

58、P is divided into four separate layers, with each layer handling a different aspect of the communication problem. The Network Interface Layer is responsible for placing packets on and receiving them from the network medium, which could be a Local Area Network (Ethernet) or Token Ring Network, or oth

59、er network technology. TCP/IP(傳輸控制協(xié)議傳輸控制協(xié)議/網(wǎng)際協(xié)議網(wǎng)際協(xié)議)被分為四個獨立的層被分為四個獨立的層,由每層由每層處理通信問題的一個不同方面。網(wǎng)絡(luò)接口層負責信息包在網(wǎng)絡(luò)處理通信問題的一個不同方面。網(wǎng)絡(luò)接口層負責信息包在網(wǎng)絡(luò)媒體上的排列和接收媒體上的排列和接收,網(wǎng)絡(luò)媒體可能是局域網(wǎng)網(wǎng)絡(luò)媒體可能是局域網(wǎng)(以太網(wǎng)以太網(wǎng))、令牌環(huán)、令牌環(huán)形網(wǎng)或其他網(wǎng)絡(luò)技術(shù)。形網(wǎng)或其他網(wǎng)絡(luò)技術(shù)。8.1.2 THE INTERNET: KEY TECHNOLOGY CONCEPTS Chapter 8 The Internet 8-23TCP/IP is independent f

60、rom any local network technology and can adapt to changes in the local level. The Internet Layer is responsible for addressing, packaging, and routing messages on the Internet. The Transport Layer is responsible for providing communication with the application by acknowledging and sequencing the packets to