1、UNIT 9 The Internet Section A The Internet1第1頁 The most notable example of an internet is the Internet (note the uppercase l ), which originated from research projects going back to the early 1960s. The goal was to develop the ability to link a variety of computer networks so that they could functio

2、n as a connected system that would not be disrupted by local disasters. 最著名互聯網例子是因特網（Internet，注意大寫）。因特網起源于20世紀60年代初研究項目。其目標是發展一個能力，將各種計算機網絡連接起來，使它們能夠作為一個不會因局部災難而瓦解互聯絡統運行。Introduction2第2頁Most of this original work was sponsored by the U.S. government through the Defense Advanced Research Projects Age

3、ncy (DARPA-pronounced DAR-pa). Over the years, the development of the lnternet 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 involving millions of computers.最初工作大多是由美國政府經過國防部

4、高級研究計劃局（DARPA讀作“DAR-pa”）發起。伴隨歲月推移，因特網開發從一個國防項目轉變成一個學術研究項目。如今，它在很大程度上是一個商業項目，連接著全世界廣域網、城域網和局域網，包括數百萬臺計算機。Introductionshifted from.to.從.轉為shift from 從.去掉（移開）3第3頁I. Internet Architecture Conceptually, the internet can be viewed as a collection of domains, each of which consists of a network or a relati

5、vely small internet operated by a single organization such as a university, company, or government agency. Each domain is an autonomous system that can be configured as the local authority desires. I. 因特網體系結構 從概念上說，因特網能夠看作是域集合。每個域由一個網絡或一個相對較小互聯網組成，由一個像大學、企業或政府機構那樣組織負責運行。每個域是一個自主系統，可依據當地管理機構愿望進行配置。In

6、ternet Architecture4第4頁It might consist of a single computer or a complex internet consisting of many LANs, MANs, and even WANs. The establishment of domains is overseen by the Internet Corporation for Assigned Names and Numbers (ICANN), 它可能由一臺計算機或一個包含許多局域網、城域網、甚至廣域網復雜互聯網組成. 域建立由互聯網名稱與數字地址分配機構（ICANN

7、）監管,Internet Architecture5第5頁which is a nonprofit corporation established to coordinate the naming of domains and the assignment of Internet addresses. 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

8、 this purpose by ICANN.這是一個非贏利企業，其成立目標是協調域命名及因特網地址分配。要在因特網上建立一個域，該域必須首先經過一個得到ICANN授權做此工作、被稱為域名注冊服務商企業進行注冊。Internet Architecture6第6頁 Once a domain has been registered, it can be attached to the existing lnternet by means of a router that connects one of the networks in the domain to a network already

9、 in the Internet. This particular router is often referred to as the domains gateway, in that it represents the domains gate to the rest of the Internet. 一個域一旦注冊，即能夠使用一個路由器連接到現有因特網上。這個路由器將該域中一個網絡與已經在因特網內一個網絡相連接。這個特定路由器常被稱為該域網關，因為它相當于該域通往因特網其余部分大門。Internet Architecture7第7頁From the point of view of a

10、single domain, the portion of the lnternet lying outside of its gateway is sometimes called the cloud, in reference to the fact that the structure of the internet outside the domains gateway is out of the domains control and is of minimal concern to the operation of the domain itself。從單個域角度看，位于其網關外面

11、那部分因特網有時被稱為“云”,這是指以下事實：其網關外面因特網結構不受其控制，而且與其本身操作也沒有什么關系。Internet Architecture就.而論is of+ 抽象n: 作為表語表示主語性質或特征。意思是“含有，具備”，如：be of success = be successful be of use = be useful8第8頁Any message being transmitted to a destination within the domain is handled within the domain; any message being transmitted t

12、o a destination outside the domain is directed toward the gateway where it is sent out into the cloud.傳輸給該域內一個目標地任何報文都在該域內處理，傳輸給該域外一個目標地任何報文都首先送至網關，然后由網關向外發送到云里。Internet Architecture9第9頁 If one stood at a domains gateway and looked out into the cloud, one could find a variety of structures. Indeed,

13、the lnternet has grown in a somewhat haphazard way as various domains have found points at which to connect to the cloud. One popular structure, however, is for the gateways of a number of domains to be connected to form a regional network of gateways. 一個人假如“站”在一個域網關處“向外看”云，就會發覺各種結構。確實，伴隨各種域找到與云建立連接

14、點，因特網也以有點隨意方式發展著。然而，一個流行結構是，將若干域網關連接在一起，形成一個由網關組成區域網絡。Internet Architecture支持/贊成，是為了.10第10頁For instance, a group of universities could choose to pool their resources to construct such a network. In turn, this regional network would be connected to a more global network to which other regional networ

15、ks attach. In this manner, that portion of the cloud takes on a hierarchical structure (Figure 9A-I).比如，一組大學能夠選擇將其資源集中起來，用于構建這么一個網絡。而這個區域網絡接著又連接到一個更大網絡上，后者上面還連接有其它區域網絡。這么，那部分云就展現出了層次結構（圖9A-1）。Internet Architecture輪番地、依次11第11頁II. Connecting to the lnternet To simplify the process of connecting to the

16、 Internet, numerous companies, called Internet service providers (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. II 連接到因特網 為了簡化連接到因特網上過程，許多稱為因特網服務提供商企業允許客戶經過企業設備將他們域連接到因特網上，或者成為企業已經建立一個域一部分Connect

17、ing to the Internet12第12頁Perhaps the least expensive connections to an ISP are obtained through temporary telephone links called dial-up connections. 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 co

18、mputer at the ISP. At this point the ISP provides lnternet access for the duration of the telephone call.與因特網服務提供商最經濟連接或許是經過暫時電話鏈路建立連接，這種連接稱為撥號連接。使用這種方法，一個人將其計算機連接到當地電話線上，然后運行一個軟件包，向因特網服務提供商一臺計算機發出呼叫。這時，因特網服務提供商就為其提供因特網訪問服務，連續時間為電話呼叫時間長度Connecting to the Internet13第13頁 This temporary connection mode

19、l is popular (and, in fact, expanding) in the cell phone /hand-held computer area. However, 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. 這種暫時連接模型在手機/手持式計算機領域比較流行（實際上應用得越來越多）

20、。然而，在位置固定應用中，暫時連接快速讓位于永久連接，這種連接經過數字用戶線路、有線電視線路和衛星鏈路等帶寬比較高系統建立Connecting to the Internetgive way to 讓路，讓步give way 讓步，屈服，垮掉14第14頁These technologies have greatly reduced the expense of broadband (high-capacity) lnternet access (which used to be availible only to large organizations that could afford th

21、e expense of dedicated lnternet connections), making todays multimedia applications accessible to home users.這些技術大大降低了寬帶（大容量）因特網訪問（曾經只提供給負擔得起專用因特網連接大型機構）費用，從而使家庭用戶也能夠訪問今天多媒體應用程序。Connecting to the Internet15第15頁 Another development taking place at the household level is that home computer systems are

22、 expanding from single computer installations to multicomputer networks, usually implemented as Ethernet bus networks. These networks gain access to the Internet 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, 在家庭層面出

23、現另外一個發展是，家用計算機系統正在從單個計算機設備擴展為多個計算機網絡，這種網絡通常實現為以太網總線網絡。這些網絡使用家里路由器訪問因特網，而該路由器經過數字用戶線路、有線電視線路或衛星鏈路與因特網服務提供商永久連接，Connecting to the Internet16第16頁making the home system a local network within a domain established by the ISP. The connection from the homes router to the local computers is often wireless.

24、That is, each computer communicates with the router by means of a small transmitter/receiver with a range of approximately 100 feet. 從而使家里系統成為因特網服務提供商建立一個域中局部網.從家中路由器到家庭局部網中計算機連接經常采取無線方式。也就是說，每臺計算機使用一部作用距離大約為100英尺小型發射機/接收機與路由器通信。Connecting to the Internet17第17頁Such wireless local networks are popula

25、r 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. Examples include office buildings, cyber cafes, public plazas and entire cities.這種無線局部網在家庭之外也很流行，被用于建立熱區。在這些熱區范圍內，任何含有沒有線上網能

26、力計算機（膝上型或手持式計算機）均可訪問因特網。熱區例子包含辦公樓、網吧、公共購物廣場以及整個城市。Connecting to the Internet18第18頁 In closing we should note that ISPs provide much more than mere access to the Internet. In many cases they are the companies that construct and maintain the Internet infrastructure. Moreover, their services generally

27、include a wide array of both hardware and software support for their customers. In fact, an ISP might provide a significant portion of the computing resources (such as data storage and data processing services) required by a client. 最終，我們應該強調，因特網服務提供商遠不止于提供因特網訪問服務。在許多情況下，它們也是構建和維護因特網基礎結構企業。而且，它們服務普通

28、包含為其用戶提供一系列廣泛硬件與軟件支持。實際上，因特網服務提供商還可能提供用戶所需計算資源（如數據存放和數據處理服務）中相當大一部分。Connecting to the Internet比.怎么樣很多19第19頁III. Internet Addressing An internet must be associated with an internet-wide addressing system that assigns an identifying address to each computer in the system. In the Internet these address

29、es are known as IP addresses. Each IP address is a pattern of 32 bits. although plans are currently underway to increase this to 128 bits. Each 32-bit address consists of two parts:III. 因特網編址 一個互聯網必須與一個互聯網范圍編址系統相聯絡，該系統給系統中每臺計算機分配一個標識地址。在因特網中，這些地址稱為IP地址。每個IP地址是一個32位模式，但人們當前正在實施將其擴展到128位計劃。每個32位地址由兩部分

30、組成：Internet Addressing20第20頁a pattern identifying the domain in which the computer resides and a pattern identifying the particular computer within the domain. The part of the address identifying the domain, the network identifier, is assigned under the authority of ICANN at the time the domain is r

31、egistered. 一部分是標識計算機所在域模式，另一部分是標識域內特定計算機模式。地址中標識域那部分，即網絡標識符，是注冊域時依據ICANN授權分配。Internet Addressing21第21頁Thus it is by means of this registration process that each domain in the Internet is assured of having a unique network identifier. The portion of the address that identifies a particular computer w

32、ithin a domain is called the host address. The host address is assigned by the domains local authority-usually a person having a job title such as network administrator or system administrator.所以，因特網中每個域是經過這個注冊過程才確保擁有一個獨特網絡標識符。地址中標識域內特定計算機那部分叫做主機地址。主機地址由域當地管理機構（通常是含有網絡管理員或系統管理員等職別人）分配。Internet Addre

33、ssing 強調句22第22頁 IP addresses are traditionally written in dotted decimal notation in which the bytes of the address are separated by periods and each byte is expressed as an integer represented in traditional base ten notation. For example, using dotted decimal notation, the pattern 5.2 would repres

34、ent the two-byte bit pattern 0000010100000010, which consists of the byte 00000101 (represented by 5) followed by the byte 00000010 (represented by 2), IP地址傳統上是用點分十進制記數法書寫。其中，地址各字節用圓點分隔，每個字節用一個整數來表示，而該整數是用傳統以10為底記數法來表示。比如，使用點分十進制記數法，5.2這個模式代表0000010100000010這個兩字節位模式，其中包含字節00000101（用5表示）和其后字節00000010

35、（用2表示）；Internet Addressing23第23頁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 the byte 00011001 (25 written in binary). Thus a computer in

36、 the domain of the Addison-Wesley publishing company might have the IP address 33,而17.12.25這個模式代表一個三字節位模式，其中包含字節00010001（這是用二進制記數法書寫17）、隨即字節00001100（用二進制書寫12）以及最終字節00011001（用二進制書寫25）。所以，位于艾迪生 韋斯利（ Addison-Wesley ） 出版企業域內一臺計算機可能擁有33這個IP地址Internet Addressing24第24頁where the first three bytes (192.207.1

37、77) 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).其中前面3個字節（192.207.177）組成網絡標識符（標識Addison-Wesley這個域），最終一個字節（133）是主機地址（標識Addison-Wesley域內一臺特定計算機）。Internet Addressing25第25

38、頁 Addresses in bit-pattern form (even when compressed using dotted decimal notation) are rarely conducive to human consumption. For this reason each domain is also assigned a unique mnemonic address known as a domain name. For example, the domain name of the Addisom-Wesley publishing company is .Not

39、e that the naming system reflects the domains classification, which in this case is commercial as indicated by the com suffix. 用位模式形式表示地址（即使經過使用點分十進制記數法壓縮）極少能夠有利于人們了解記憶。因為這個原因，每個域還分配了一個獨特助記地址，稱為域名。例如，艾迪生韋斯利出版企業域名是。注意這個命名系統反映了域分類，如后綴com所示,艾迪生韋斯利出版企業域屬于商業性。Internet Addressing 消費、消耗；了解、記憶26第26頁Such a c

40、lassification is called a top-level domain (TLD). There are numerous TLDs, including edu for educational institutions, gov for U.S. government institutions,org for nonprofit organizations, museum for museums, info for unrestricted use, and net, which was originally intended for lnternet service prov

41、iders but is now used on a much broader scale.這么類別稱為頂級域名(TLD).頂級域名為數不少，包含表示教育機構edu、表示美國政府機構gov、表示非贏利機構org、表示博物館museum、表示無限制使用info以及net, net最初打算用于表示因特網服務提供商，但現在使用范圍要廣泛得多。Internet Addressing27第27頁In addition to these general TLDs, there are also two-letter TLDs for specific countries (called country-c

42、ode TLDs) such as au for Australia and ca for Canada.除了這些普通頂級域名之外，還有用于表示詳細國家兩字母頂級域名（稱為國家代碼頂級域名），如表示澳大利亞au和表示加拿大ca。Internet Addressing28第28頁Once a domain has a mnemonic name, its local authority is free to extend it to obtain mnemonic names for the machines within its domain.For example, an individua

43、l machine within the domain might be identified as . 一旦一個域擁有了一個助記名，其當地管理機構就可自由地擴展該助記名，從而為域內計算機取得助記名。比如， 位于 域內一臺計算機可能被標識為。Internet Addressing29第29頁 We should emphasize that the dotted notation used in mnemonic addresses is not related to the dotted decimal notation used to represent IP addresses. Ins

44、tead, the sections in a mnemonic address identify the computers location within a hierarchical classification system. 應該強調是，用于助記地址點分表示法與用于表示IP地址點分十進制記數法沒相關系。相反，助記地址各部分標識計算機在一個層次分類系統中位置。Internet Addressing30第30頁In particular, the address indicates that the computer known as ssenterprise is within the

45、 institution aw within the class (or TLD) of commercial domains com. In the case of large domains, a local authority might break its domain into subdomains, in which case the mnemonic addresses of the computers within the domain might be longer. 詳細來說這個地址表示：稱為ssenterprise計算機位于aw這個機構內，而aw則屬于com這個商業性域類

46、（或頂級域名）。在大型域情況下，當地管理機構可能將其域分成子域。在這種情況下，域中計算機助記地址可能比較長。Internet Addressing1. 把.分成。2. 打斷，打攪 ones thought3. 闖進 the house31第31頁For example, suppose Nowhere University was assigned the domain name and chose to divide its domain into subdomains. Then, a computer at Nowhere University could have an address

47、 such as , meaning that the computer r2d2 is in the subdomain compsc within the domain nowhereu within the class of educational domains edu.比如，假設烏有大學被賦予這個域名，并選擇將其域分成子域。那么，烏有大學一臺計算機就可能含有像psc.nowhereu. edu這么一個地址。該地址表示：稱為r2d2計算機位于子域compsc中，而子域compsc則在nowhereu這個域中，而nowhereu這個域又屬于edu這個教育性域類。Internet Addr

48、essing32第32頁 Each domains local authority is responsible for maintaining a directory containing the mnemonic address and the corresponding IP address of those computers within its domain. This directory is implemented on a designated computer within the domain in the form of a server, called a name server, that responds