1、UNIT 9 The Internet,Section A The Internet,2/34,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 functi
2、on as a connected system that would not be disrupted by local disasters.,最著名的互联网例子是因特网（Internet，注意大写的）。因特网起源于20世纪60年代初的研究项目。其目标是发展一种能力，将各种计算机网络连接起来，使它们能够作为一个不会因局部灾难而瓦解的互联系统运行。,Introduction,3/34,Most of this original work was sponsored by the U.S. government through the Defense Advanced Research Proj
3、ects Agency (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.,最初的工作大
4、多是由美国政府通过国防部高级研究计划局（DARPA读作“DAR-pa”）发起的。随着岁月的推移，因特网的开发从一个国防项目转变成一个学术研究项目。如今，它在很大程度上是一个商业项目，连接着全世界的广域网、城域网和局域网，涉及数百万台计算机。,Introduction,shifted from.to.从.转为 shift from 从.去掉（移开）,4/34,I. Internet Architecture Conceptually, the internet can be viewed as a collection of domains, each of which consists of
5、a network or a relatively 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. 因特网体系结构 从概念上说，因特网可以看作是域的集合。每个域由一个网络或一个相对较小的互联网组成，由一个像大学、公司或政府机构那样的组织负责运行。每个域是一
6、个自主系统，可根据本地管理机构的愿望进行配置。,Internet Architecture,5/34,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),它可能由一台计算机或一个包含许多局域网、城域网、甚至广域网的复杂互联网
7、组成.域的建立由互联网名称与数字地址分配机构（ICANN）监管,Internet Architecture,6/34,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
8、, that have been delegated for this purpose by ICANN.,这是一个非赢利公司，其成立的目的是协调域的命名及因特网地址的分配。要在因特网上建立一个域，该域必须首先通过一个得到ICANN授权做此工作、被称为域名注册服务商的公司进行注册。,Internet Architecture,7/34,Once a domain has been registered, it can be attached to the existing lnternet by means of a router that connects one of the networ
9、ks in the domain to a network already 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.,一个域一旦注册，即可以使用一个路由器连接到现有的因特网上。这个路由器将该域中的一个网络与已经在因特网内的一个网络相连接。这个特定的路由器常被称为该域的网关，因为它相当于该域通往因特网其余部分的大门。,Internet
10、Architecture,8/34,From the point of view of a 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
11、operation of the domain itself。,从单个域的角度看，位于其网关外面的那部分因特网有时被称为“云”,这是指以下的事实：其网关外面的因特网结构不受其控制，而且与其本身的操作也没有什么关系。,Internet Architecture,就.而论,is of+ 抽象n: 作为表语表示主语的性质或特征。意思是“具有，具备”，如：be of success = be successful be of use = be useful,9/34,Any message being transmitted to a destination within the domain is
12、handled within the domain; any message being transmitted to a destination outside the domain is directed toward the gateway where it is sent out into the cloud.,传输给该域内一个目的地的任何报文都在该域内处理，传输给该域外一个目的地的任何报文都首先送至网关，然后由网关向外发送到云里。,Internet Architecture,10/34,If one “stood“ at a domains gateway and “looked o
13、ut“ into the cloud, one could find a variety of structures. Indeed, 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
14、network of gateways.,一个人如果“站”在一个域的网关处“向外看”云，就会发现各种结构。的确，随着各种域找到与云建立连接的点，因特网也以有点随意的方式发展着。然而，一种流行的结构是，将若干域的网关连接在一起，形成一个由网关组成的区域网络。,Internet Architecture,支持/赞成，是为了.,11/34,For instance, a group of universities could choose to pool their resources to construct such a network. In turn, this regional netwo
15、rk would be connected to a more global network to which other regional networks attach. In this manner, that portion of the cloud takes on a hierarchical structure (Figure 9A-I).,例如，一组大学可以选择将其资源集中起来，用于构建这样一个网络。而这个区域网络接着又连接到一个更大的网络上，后者上面还连接有其他的区域网络。这样，那部分云就呈现出了层次结构（图9A-1）。,Internet Architecture,轮流地、依
16、次,12/34,II. Connecting to the lnternetTo simplify the process of connecting to the 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.,I
17、I 连接到因特网为了简化连接到因特网上的过程，许多称为因特网服务提供商的公司允许客户通过公司的设备将他们的域连接到因特网上，或者成为公司已经建立的一个域的一部分,Connecting to the Internet,13/34,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 comput
18、er to the local telephone line and executes a software package that places a call to a computer at the ISP. At this point the ISP provides lnternet access for the duration of the telephone call.,与因特网服务提供商最经济的连接或许是通过临时电话链路建立的连接，这种连接称为拨号连接。使用这种方法，一个人将其计算机连接到当地电话线上，然后运行一个软件包，向因特网服务提供商的一台计算机发出呼叫。这时，因特网服
19、务提供商就为其提供因特网访问服务，持续时间为电话呼叫的时间长度,Connecting to the Internet,14/34,This temporary connection model 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
20、 such as DSL, cable television lines, and satellite links.,这种临时连接模型在手机/手持式计算机领域比较流行（实际上应用得越来越多）。然而，在位置固定的应用中，临时连接快速让位于永久连接，这种连接通过数字用户线路、有线电视线路和卫星链路等带宽比较高的系统建立,Connecting to the Internet,give way to 让路，让步 give way 让步，屈服，垮掉,15/34,These technologies have greatly reduced the expense of broadband (high-c
21、apacity) lnternet access (which used to be availible only to large organizations that could afford the expense of dedicated lnternet connections), making todays multimedia applications accessible to home users.,这些技术大大降低了宽带（大容量）因特网访问（曾经只提供给负担得起专用因特网连接的大型机构）的费用，从而使家庭用户也可以访问今天的多媒体应用程序。,Connecting to th
22、e Internet,16/34,Another 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. These networks gain access to the Internet by means of a router within the
23、home that is permanently connected to an ISP via DSL, a cable television line, or a satellite link,在家庭层面出现的另外一个发展是，家用计算机系统正在从单个计算机设备扩展为多个计算机的网络，这种网络通常实现为以太网总线网络。这些网络使用家里的路由器访问因特网，而该路由器通过数字用户线路、有线电视线路或卫星链路与因特网服务提供商永久连接，,Connecting to the Internet,17/34,making the home system a local network within a
24、domain established by the ISP. The connection from the homes router to the local computers is often wireless. That is, each computer communicates with the router by means of a small transmitter/receiver with a range of approximately 100 feet.,从而使家里的系统成为因特网服务提供商建立的一个域中的局部网.从家中路由器到家庭局部网中计算机的连接常常采用无线方式
25、。也就是说，每台计算机使用一部作用距离大约为100英尺的小型发射机/接收机与路由器通信。,Connecting to the Internet,18/34,Such wireless local 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. Example
26、s include office buildings, cyber cafes, public plazas and entire cities.,这种无线局部网在家庭之外也很流行，被用于建立热区。在这些热区的范围内，任何具有无线上网能力的计算机（膝上型或手持式计算机）均可访问因特网。热区的例子包括办公楼、网吧、公共购物广场以及整个城市。,Connecting to the Internet,19/34,In closing we should note that ISPs provide much more than mere access to the Internet. In many
27、cases they are the companies that construct and maintain the Internet infrastructure. Moreover, their services generally 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 storag
28、e and data processing services) required by a client.,最后，我们应该强调，因特网服务提供商远不止于提供因特网访问服务。在许多情况下，它们也是构建和维护因特网基础结构的公司。而且，它们的服务一般包括为其顾客提供一系列广泛的硬件与软件支持。事实上，因特网服务提供商还可能提供顾客所需的计算资源（如数据存储和数据处理服务）中的相当大一部分。,Connecting to the Internet,比.怎么样很多,20/34,III. Internet AddressingAn internet must be associated with an i
29、nternet-wide addressing system that assigns an identifying address to each computer in the system. In the Internet these addresses 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 t
30、wo parts:,III. 因特网编址一个互联网必须与一个互联网范围的编址系统相联系，该系统给系统中的每台计算机分配一个标识地址。在因特网中，这些地址称为IP地址。每个IP地址是一个32位模式，但人们当前正在实施将其扩展到128位的计划。每个32位地址由两部分构成：,Internet Addressing,21/34,a pattern identifying the domain in which the computer resides and a pattern identifying the particular computer within the domain. The par
31、t of the address identifying the domain, the network identifier, is assigned under the authority of ICANN at the time the domain is registered.,一部分是标识计算机所在域的模式，另一部分是标识域内特定计算机的模式。地址中标识域的那部分，即网络标识符，是注册域时根据ICANN的授权分配的。,Internet Addressing,22/34,Thus it is by means of this registration process that each
32、 domain in the Internet is assured of having a unique network identifier. The portion of the address that identifies a particular computer within 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 admin
33、istrator or system administrator.,因此，因特网中的每个域是通过这个注册过程才确保拥有一个独特网络标识符的。地址中标识域内特定计算机的那部分叫做主机地址。主机地址由域的本地管理机构（通常是具有网络管理员或系统管理员等职别的人）分配。,Internet Addressing,强调句,23/34,IP addresses are traditionally written in dotted decimal notation in which the bytes of the address are separated by periods and each byt
34、e is expressed as an integer represented in traditional base ten notation. For example, using dotted decimal notation, the pattern 5.2 would represent the two-byte bit pattern 0000010100000010, which consists of the byte 00000101 (represented by 5) followed by the byte 00000010 (represented by 2),IP
35、地址传统上是用点分十进制记数法书写的。其中，地址的各字节用圆点分隔，每个字节用一个整数来表示，而该整数是用传统的以10为底的记数法来表示的。例如，使用点分十进制记数法，5.2这个模式代表0000010100000010这个两字节位模式，其中包含字节00000101（用5表示）和其后的字节00000010（用2表示）；,Internet Addressing,24/34,and the pattern 17.12.25 would represent the three-byte bit pattern consisting of the byte 00010001 (which is 17 w
36、ritten 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 the domain of the Addison-Wesley publishing company might have the IP address 192.207.177.133,而17.12.25这个模式代表一个三字节位模式，其中包含字节00010001（这是用二进制记数法书写的
37、17）、随后的字节00001100（用二进制书写的12）以及最后的字节00011001（用二进制书写的25）。因此，位于艾迪生 韦斯利（ Addison-Wesley ） 出版公司域内的一台计算机可能拥有192.207.177.133这个IP地址,Internet Addressing,25/34,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 addr
38、ess (identifying a particular computer within Addison-Wesleys domain).,其中前面的3个字节（192.207.177）构成网络标识符（标识Addison-Wesley这个域），最后一个字节（133）是主机地址（标识Addison-Wesley域内的一台特定计算机）。,Internet Addressing,26/34,Addresses in bit-pattern form (even when compressed using dotted decimal notation) are rarely conducive to
39、 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 .Note that the naming system reflects the domains classification, which in this case is commercial as indicated
40、by the com suffix.,用位模式形式表示的地址（即使经过使用点分十进制记数法压缩）很少能够有助于人们理解记忆。由于这个原因，每个域还分配了一个独特的助记地址，称为域名。例如，艾迪生韦斯利出版公司的域名是。注意这个命名系统反映了域的分类，如后缀com所示,艾迪生韦斯利出版公司的域属于商业性的。,Internet Addressing,消费、消耗；理解、记忆,27/34,Such a classification is called a top-level domain (TLD). There are numerous TLDs, including edu for educati
41、onal 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 providers but is now used on a much broader scale.,这样的类别称为顶级域名(TLD).顶级域名为数不少，包括表示教育机构的edu、表示美国政府机构的gov、表
42、示非赢利机构的org、表示博物馆的museum、表示无限制使用的info以及net, net最初打算用于表示因特网服务提供商，但现在使用的范围要广泛得多。,Internet Addressing,28/34,In addition to these general TLDs, there are also two-letter TLDs for specific countries (called country-code TLDs) such as au for Australia and ca for Canada.,除了这些一般的顶级域名之外，还有用于表示具体国家的两字母顶级域名（称为国
43、家代码顶级域名），如表示澳大利亚的au和表示加拿大的ca。,Internet Addressing,29/34,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 individual machine within the domain might be identified as .,一旦一个域拥有了一个助记名，其本地管理机构就可自由地扩展该
44、助记名，从而为域内的计算机取得助记名。例如， 位于 域内的一台计算机可能被标识为。,Internet Addressing,30/34,We should emphasize that the dotted notation used in mnemonic addresses is not related to the dotted decimal notation used to represent IP addresses. Instead, the sections in a mnemonic address identify the computers location within
45、 a hierarchical classification system.,应该强调的是，用于助记地址的点分表示法与用于表示IP地址的点分十进制记数法没有关系。相反，助记地址的各部分标识计算机在一个层次分类系统中的位置。,Internet Addressing,31/34,In particular, the address indicates that the computer known as ssenterprise is within the institution aw within the class (or TLD) of commercial domains com. In
46、 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.,具体来说这个地址表示：称为ssenterprise的计算机位于aw这个机构内，而aw则属于com这个商业性域类（或顶级域名）。在大型域的情况下，本地管理机构可能将其域分成子域。在这种情况下，域中计算机的助记地址可能比较长。,Internet Addr
47、essing,1. 把.分成。 2. 打断，打扰 ones thought 3. 闯入 the house,32/34,For example, suppose Nowhere University was assigned the domain name nowhereu.edu and chose to divide its domain into subdomains. Then, a computer at Nowhere University could have an address such as psc.nowhereu.edu, meaning that the comput
48、er r2d2 is in the subdomain compsc within the domain nowhereu within the class of educational domains edu.,例如，假设乌有大学被赋予nowhereu.edu这个域名，并选择将其域分成子域。那么，乌有大学的一台计算机就可能具有像psc.nowhereu. edu这样的一个地址。该地址表示：称为r2d2的计算机位于子域compsc中，而子域compsc则在nowhereu这个域中，而nowhereu这个域又属于edu这个教育性域类。,Internet Addressing,33/34,Each
49、 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 to requests regarding address information.,每个域的本地管理机构负责维持一个目录，里面含有该域中每台计算机的助记地址和相应的IP地址。这个目录在该域中充当服务器的一台指定计算机上实现。这个服务器叫做名称服务器，它对有关地址信息的请求作出响应。,
