Computer English Unit 9 The Internet(計(jì)算機(jī)英語 第九單元 因特網(wǎng))

1、Unit 9 The Internet第九單元： 因特網(wǎng) Section A The Internet課文A： 因特網(wǎng) The most notable example of an internet is the Internet (note the uppercase ), which originated from research projects going back to the early 1960s.最著名的互聯(lián)網(wǎng)例子是因特網(wǎng)（Internet，注意大寫的）。因特網(wǎng)起源于20世紀(jì)60年代初的研究項(xiàng)目。The goal was to develop the ability to l

2、ink a variety of computer networks so that they could function as a connected system that would not be disrupted by local disasters.其目標(biāo)是發(fā)展一種能力，將各種計(jì)算機(jī)網(wǎng)絡(luò)連接起來，使它們能夠作為一個不會因局部災(zāi)難而瓦解的互聯(lián)系統(tǒng)運(yùn)行。Most of this original work was sponsored by the U.S. government through the Defense Advanced Research Projects Agency

3、 (DARPA- pronounced DAR-pa).最初的工作大多是由美國政府通過國防部高級研究計(jì)劃局（DARPA讀作“DAR-pa”）發(fā)起的。Over the years, the development of the Internet shifted from a defense project to an academic research project, and today it is largely a commercial undertaking that links a worldwide combination of WANs, MANs, and LANs involv

4、ing millions of computers.隨著歲月的推移，因特網(wǎng)的開發(fā)從一個國防項(xiàng)目轉(zhuǎn)變成一個學(xué)術(shù)研究項(xiàng)目。如今，它在很大程度上是一個商業(yè)項(xiàng)目，連接著全世界的廣域網(wǎng)、城域網(wǎng)和局域網(wǎng)，涉及數(shù)百萬臺計(jì)算機(jī)。. Internet architecture一、因特網(wǎng)體系結(jié)構(gòu)Conceptually, the Internet can be viewed as a collection of domains, each of which consists of a network or a relatively small internet operated by a single organ

5、ization such as a university, company, or government agency.從概念上說，因特網(wǎng)可以看作是域的集合。每個域由一個網(wǎng)絡(luò)或一個相對較小的互聯(lián)網(wǎng)組成，由一個像大學(xué)、公司或政府機(jī)構(gòu)那樣的組織負(fù)責(zé)運(yùn)行。Each domain is an autonomous system that can be configured as the local authority desires.每個域是一個自主系統(tǒng)，可根據(jù)本地管理機(jī)構(gòu)的愿望進(jìn)行配置。It might consist of a single computer or a complex intern

6、et consisting of many LANs, MANs, and even WANs.它可能由一臺計(jì)算機(jī)或一個包含許多局域網(wǎng)、城域網(wǎng)、甚至廣域網(wǎng)的復(fù)雜互聯(lián)網(wǎng)組成。The establishment of domains is overseen by the Internet Corporation for Assigned Names and Numbers (ICANN), which is a nonprofit corporation established to coordinate the naming of domains and the assignment of In

7、ternet addresses.域的建立由互聯(lián)網(wǎng)名稱與數(shù)字地址分配機(jī)構(gòu)（ICANN）監(jiān)管。這是一個非贏利公司，其成立的目的是協(xié)調(diào)域的命名及因特網(wǎng)地址的分配。To establish a domain on the Internet, the domain must first be registered via one of the companies, called registrars, that have been delegated for this purpose by ICANN.要在因特網(wǎng)上建立一個域，該域必須首先通過一個得到ICANN授權(quán)做此工作、被稱為域名注冊服務(wù)商的公司進(jìn)

8、行注冊。Once a domain has been registered, it can be attached to the existing Internet by means of a router that connects one of the networks in the domain to a network already in the Internet.一個域一旦注冊，即可以使用一個路由器連接到現(xiàn)有的因特網(wǎng)上。這個路由器將該域中的一個網(wǎng)絡(luò)與已經(jīng)在因特網(wǎng)內(nèi)的一個網(wǎng)絡(luò)相連接。This particular router is often referred to as the

9、domains gateway, in that it represents the domains gate to the rest of the Internet.這個特定的路由器常被稱為該域的網(wǎng)關(guān)，因?yàn)樗喈?dāng)于該域通往因特網(wǎng)其余部分的大門。From the point of view of a single domain, the portion of the Internet lying outside of its gateway is sometimes called the cloud, in reference to the fact that the structure of

10、 the Internet outside the domains gateway is out of the domains control and is of minimal concern to the operation of the domain itself.從單個域的角度看，位于其網(wǎng)關(guān)外面的那部分因特網(wǎng)有時被稱為“云”，這是指以下的事實(shí)：其網(wǎng)關(guān)外面的因特網(wǎng)結(jié)構(gòu)不受其控制，而且與其本身的操作也沒有什么關(guān)系。Any message being transmitted to a destination within the domain is handled within the do

11、main; any message being transmitted to an destination outside the domain is directed toward the gateway where it is sent out into the cloud.傳輸給該域內(nèi)一個目的地的任何報(bào)文都在該域內(nèi)處理，傳輸給該域外一個目的地的任何報(bào)文都首先送至網(wǎng)關(guān)，然后由網(wǎng)關(guān)向外發(fā)送到云里。If one “stood” at a domains gateway and “l(fā)ooked out ” into the cloud, one could find a variety of s

12、tructures.一個人如果“站”在一個域的網(wǎng)關(guān)處“向外看”云，就會發(fā)現(xiàn)各種結(jié)構(gòu)。Indeed, the Internet has grown in a somewhat haphazard way as various domains have found points at which to connect to the cloud.的確，隨著各種域找到與云建立連接的點(diǎn)，因特網(wǎng)也以有點(diǎn)隨意的方式發(fā)展著。One popular structure, however, is for the gateways of a number of domains to be connected to

13、form a regional network of gateways.然而，一種流行的結(jié)構(gòu)是，將若干域的網(wǎng)關(guān)連接在一起，形成一個由網(wǎng)關(guān)組成的區(qū)域網(wǎng)絡(luò)。For instance, a group of universities could choose to pool their resources to construct such a network.例如，一組大學(xué)可以選擇將其資源集中起來，用于構(gòu)建這樣一個網(wǎng)絡(luò)。In turn, this regional network would be connected to a more global network to which other

14、regional networks attach.而這個區(qū)域網(wǎng)絡(luò)接著又連接到一個更大的網(wǎng)絡(luò)上，后者上面還連接有其他的區(qū)域網(wǎng)絡(luò)。In this manner, that portion of the cloud takes on a hierarchical structure.這樣，那部分云就呈現(xiàn)出了層次結(jié)構(gòu)（圖9A-1）。. Connecting to the Internet二、連接到因特網(wǎng)To simplify the process of connecting to the Internet, numerous companies, called Internet service pr

15、oviders (ISPs), allow customers to connect their domains to the Internet via the ISPs equipment or to become a part of a domain already established by the ISP.為了簡化連接到因特網(wǎng)上的過程，許多稱為因特網(wǎng)服務(wù)提供商的公司允許客戶通過公司的設(shè)備將他們的域連接到因特網(wǎng)上，或者成為公司已經(jīng)建立的一個域的一部分。Perhaps the least expensive connections to an ISP are obtained throu

16、gh temporary telephone links called dial-up connections.與因特網(wǎng)服務(wù)提供商最經(jīng)濟(jì)的連接或許是通過臨時電話鏈路建立的連接，這種連接稱為撥號連接。Using this approach, an individual connects his or her computer to the local telephone line and executes a software package that places a call to a computer at the ISP.使用這種方法，一個人將其計(jì)算機(jī)連接到當(dāng)?shù)仉娫捑€上，然后運(yùn)行一個軟件

17、包，向因特網(wǎng)服務(wù)提供商的一臺計(jì)算機(jī)發(fā)出呼叫。At this point the ISP provides Internet access for the duration of the telephone call.這時，因特網(wǎng)服務(wù)提供商就為其提供因特網(wǎng)訪問服務(wù)，持續(xù)時間為電話呼叫的時間長度。This temporary connection model is popular (and, in fact, expanding) in the cell-phone/hand-held computer arena.這種臨時連接模型在手機(jī)/手持式計(jì)算機(jī)領(lǐng)域比較流行（實(shí)際上應(yīng)用得越來越多）。Howe

18、ver, in fixed location applications it is rapidly giving way to permanent connections through higher bandwidth systems such as DSL, cable television lines, and satellite links.然而，在位置固定的應(yīng)用中，臨時連接快速讓位于永久連接，這種連接通過數(shù)字用戶線路、有線電視線路和衛(wèi)星鏈路等帶寬比較高的系統(tǒng)建立。These technologies have greatly reduced the expense of broadb

19、and (high-capacity) Internet access (which used to be available only to large organizations that could afford the expense of dedicated Internet connections), making todays multimedia applications accessible to home users.這些技術(shù)大大降低了寬帶（大容量）因特網(wǎng)訪問（曾經(jīng)只提供給負(fù)擔(dān)得起專用因特網(wǎng)連接的大型機(jī)構(gòu)）的費(fèi)用，從而使家庭用戶也可以訪問今天的多媒體應(yīng)用程序。Another

20、 development taking place at the household level is that home computer systems are expanding from single computer installations to multicomputer networks, usually implemented as Ethernet bus networks.在家庭層面出現(xiàn)的另外一個發(fā)展是，家用計(jì)算機(jī)系統(tǒng)正在從單個計(jì)算機(jī)設(shè)備擴(kuò)展為多個計(jì)算機(jī)的網(wǎng)絡(luò)，這種網(wǎng)絡(luò)通常實(shí)現(xiàn)為以太網(wǎng)總線網(wǎng)絡(luò)。These networks gain access to the Inte

21、rnet by means of a router within the home that is permanently connected to an ISP via DSL, a cable television line, or a satellite link, making the home system a local network within a domain established by the ISP.這些網(wǎng)絡(luò)使用家里的路由器訪問因特網(wǎng)，而該路由器通過數(shù)字用戶線路、有線電視線路或衛(wèi)星鏈路與因特網(wǎng)服務(wù)提供商永久連接，從而使家里的系統(tǒng)成為因特網(wǎng)服務(wù)提供商建立的一個域中的局部

22、網(wǎng)。The connection from the homes router to the local computers is often wireless.從家中路由器到家庭局部網(wǎng)中計(jì)算機(jī)的連接常常采用無線方式。That is, each computer communicates with the router by means of a small transmitter/receiver with a range of approximately 100 feet.也就是說，每臺計(jì)算機(jī)使用一部作用距離大約為100英尺的小型發(fā)射機(jī)/接收機(jī)與路由器通信。Such wireless loc

23、al networks are popular outside the home as well where they are used to create hotspots in which any wireless-enabled computer (laptop or hand held) that comes within range can access the Internet.這種無線局部網(wǎng)在家庭之外也很流行，被用于建立熱區(qū)。在這些熱區(qū)的范圍內(nèi)，任何具有無線上網(wǎng)能力的計(jì)算機(jī)（膝上型或手持式計(jì)算機(jī)）均可訪問因特網(wǎng)。Examples include office buildings,

24、 “cyber cafes”,public plaza, and entire cities.熱區(qū)的例子包括辦公樓、網(wǎng)吧、公共購物廣場以及整個城市。In closing we should note that ISPs provide much more than mere access to the Internet.最后，我們應(yīng)該強(qiáng)調(diào)，因特網(wǎng)服務(wù)提供商遠(yuǎn)不止于提供因特網(wǎng)訪問服務(wù)。In many cases they are the companies that construct and maintain the Internet infrastructure.在許多情況下，它們也是構(gòu)建和

25、維護(hù)因特網(wǎng)基礎(chǔ)結(jié)構(gòu)的公司。Moreover, their services generally include a wide array of both hardware and software support for their customers.而且，它們的服務(wù)一般包括為其顧客提供一系列廣泛的硬件與軟件支持。In fact, an ISP might provide a significant portion of the computing resources (such as data storage and data processing services) required b

26、y a client.事實(shí)上，因特網(wǎng)服務(wù)提供商還可能提供顧客所需的計(jì)算資源（如數(shù)據(jù)存儲和數(shù)據(jù)處理服務(wù)）中的相當(dāng)大一部分。. Internet Addressing三、因特網(wǎng)編址An internet must be associated with an internet-wide addressing system that assigns an identifying address to each computer in the system.一個互聯(lián)網(wǎng)必須與一個互聯(lián)網(wǎng)范圍的編址系統(tǒng)相聯(lián)系，該系統(tǒng)給系統(tǒng)中的每臺計(jì)算機(jī)分配一個標(biāo)識地址。In the Internet theses addre

27、sses are known as IP addresses.在因特網(wǎng)中，這些地址稱為IP地址。Each IP address is a pattern of 32 bits, although plans are currently underway to increase this to 128 bits.每個IP地址是一個32位模式，但人們當(dāng)前正在實(shí)施將其擴(kuò)展到128位的計(jì)劃。Each 32-bit address consists of two parts:每個32位地址由兩部分構(gòu)成：a pattern identifying the domain in which the compu

28、ter resides and a pattern identifying the particular computer within the domain.一部分是標(biāo)識計(jì)算機(jī)所在域的模式，另一部分是標(biāo)識域內(nèi)特定計(jì)算機(jī)的模式。The part of the address identifying the domain, the network identifier, is assigned under the authority of ICANN at the time the domain is registered.地址中標(biāo)識域的那部分，即網(wǎng)絡(luò)標(biāo)識符，是注冊域時根據(jù)ICANN的授權(quán)分配的

29、。Thus it is by means of this registration process that each domain in the Internet is assured of having a unique network identifier.因此，因特網(wǎng)中的每個域是通過這個注冊過程才確保擁有一個獨(dú)特網(wǎng)絡(luò)標(biāo)識符的。The portion of the address that identifies a particular computer within a domain is called the host address.地址中標(biāo)識域內(nèi)特定計(jì)算機(jī)的那部分叫做主機(jī)地址。T

30、he host address is assigned by the domains local authority-usually a person having a job title such as network administrator or system administrator.主機(jī)地址由域的本地管理機(jī)構(gòu)（通常是具有網(wǎng)絡(luò)管理員或系統(tǒng)管理員等職別的人）分配。IP address are traditionally written in dotted decimal notation in which the bytes of the address are separated

31、by periods and each byte is expressed as an integer represented in traditional base ten notation.IP地址傳統(tǒng)上是用點(diǎn)分十進(jìn)制記數(shù)法書寫的。其中，地址的各字節(jié)用圓點(diǎn)分隔，每個字節(jié)用一個整數(shù)來表示，而該整數(shù)是用傳統(tǒng)的以10為底的記數(shù)法來表示的。For example, using dotted decimal notation, the pattern 5.2 would represent the two-byte bit pattern 0000010100000010, which consis

32、ts of the byte 00000101 (represented by 5) followed by the byte 00000010 (represented by 2), and the pattern 17.12.25 would represent the three-byte bit pattern consisting of the byte 00010001 (which is 17 written in binary notation), followed by the byte 00001100 (12 written in binary), followed by

33、 the byte 00011001 (25 written in binary).例如，使用點(diǎn)分十進(jìn)制記數(shù)法，5.2這個模式代表0000010100000010這個兩字節(jié)位模式，其中包含字節(jié)00000101（用5表示）和其后的字節(jié)00000010（用2表示）；而17.12.25這個模式代表一個三字節(jié)位模式，其中包含字節(jié)00010001（這是用二進(jìn)制記數(shù)法書寫的17）、隨后的字節(jié)00001100（用二進(jìn)制書寫的12）以及最后的字節(jié)00011001（用二進(jìn)制書寫的25）。Thus a computer in the domain of the Addison-Wesley publishing

34、company might have the IP address 33, where the first three bytes (192.207.177) form the network identifier (identifying the Addison-Wesley domain) and the last byte (133) is the host address (identifying a particular computer within Addison-Wesleys domain).因此，位于艾迪生 韋斯利（ Addison-Wesley

35、） 出版公司域內(nèi)的一臺計(jì)算機(jī)可能擁有33這個IP地址，其中前面的3個字節(jié)（192.207.177）構(gòu)成網(wǎng)絡(luò)標(biāo)識符（標(biāo)識Addison-Wesley這個域），最后一個字節(jié)（133）是主機(jī)地址（標(biāo)識Addison-Wesley域內(nèi)的一臺特定計(jì)算機(jī)）。 Addresses in bit-pattern form (even when compressed using dotted decimal notation) are rarely conducive to human consumption.用位模式形式表示的地址（即使經(jīng)過使用點(diǎn)分十進(jìn)制記數(shù)法壓縮）很少能夠有助于人們

36、理解記憶。For this reason each domain is also assigned a unique mnemonic address known as a domain name.由于這個原因，每個域還分配了一個獨(dú)特的助記地址，稱為域名。For example, the domain name of the Addison-Wesley publishing company is .例如，艾迪生韋斯利出版公司的域名是。Note that the naming system reflects the domains classification, which in this c

37、ase is commercial as indicated by the com suffix.注意這個命名系統(tǒng)反映了域的分類。如后綴com所示，艾迪生韋斯利出版公司的域?qū)儆谏虡I(yè)性的。Such classification is called a top-level domain (TLD).這樣的類別稱為頂級域名。There are numerous TLDs, including edu for educational institutions, gov for U.S. government institutions, org for nonprofit organizations,

38、museumfor museums, info for unrestricted use, and net, which was originally intended for Internet service providers but is now used on a much broader scale.頂級域名為數(shù)不少，包括表示教育機(jī)構(gòu)的edu、表示美國政府機(jī)構(gòu)的gov、表示非贏利機(jī)構(gòu)的org、表示博物館的museum、表示無限制使用的info以及最初打算用于表示因特網(wǎng)服務(wù)提供商，但現(xiàn)在使用的范圍要廣泛得多。In addition to these general TLD

39、s, there are also two-letter TLDs for specific countries (called country-code TLDs) such as au for Australia and ca for Canada.除了這些一般的頂級域名之外，還有用于表示具體國家的兩字母頂級域名（稱為國家代碼頂級域名），如表示澳大利亞的au和表示加拿大的ca。Once a domain has a mnemonic name, its local authority is free to extend it to obtain mnemonic manes for the

40、 machines within its domain.一旦一個域擁有了一個助記名，其本地管理機(jī)構(gòu)就可自由地?cái)U(kuò)展該助記名，從而為域內(nèi)的計(jì)算機(jī)取得助記名。For example, an individual machine within the domain might be identified as .例如， 位于 域內(nèi)的一臺計(jì)算機(jī)可能被標(biāo)識為。We should emphasize that the dotted notation used in mnemonic addresses is not related to the dotted decimal notation used to

41、 represent IP addresses.應(yīng)該強(qiáng)調(diào)的是，用于助記地址的點(diǎn)分表示法與用于表示IP地址的點(diǎn)分十進(jìn)制記數(shù)法沒有關(guān)系。Instead, the sections in a mnemonic address identify the computers location within a hierarchical classification system.相反，助記地址的各部分標(biāo)識計(jì)算機(jī)在一個層次分類系統(tǒng)中的位置。In particular, the address indicates that the computer known as ssenterprise is with

42、in the institution aw within the class (or TLD) of commercial domain com.具體來說，這個地址表示：稱為ssenterprise的計(jì)算機(jī)位于aw這個機(jī)構(gòu)內(nèi)，而aw則屬于com這個商業(yè)性域類（或頂級域名）。In the case of large domains, a local authority might break its domain in to subdomains, in which case the mnemonic addresses of the computers within the domain mi

43、ght be longer. For example, suppose Nowhere University was assigned the domain name nowhereu. edu and chose to divide its domain into subdomains.在大型域的情況下，本地管理機(jī)構(gòu)可能將其域分成子域。在這種情況下，域中計(jì)算機(jī)的助記地址可能比較長。Then, a computer at Nowhere University could have an address such as , meaning that the computer r2d2 is in the subdomain compsc within the domain nowhereu wi