计算机英语刘艺王春生第4版省公共课一等奖全国赛课获奖课件.pptx

UNIT 9 The Internet Section A The Internet1第1页 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 function as a connected system that would not be disrupted by local disasters.最著名著名互联网例子是因特网（Internet，注意大写）。因特网起源于20世纪60年代初研究项目。其目标是发展一个能力，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瓦解互联络统运行。Introduction2第2页Most of this original work was sponsored by the U.S.government through the Defense Advanced Research Projects 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.最初工作大多是由美国政府经过国防部高级研究计划局（DARPA读作“DAR-pa”）发起。伴随岁月推移，因特网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项目，连接着全世界广域网、城域网和局域网，包括数百万台计算机。Introductionshifted from.to.从.转为shift from 从.去掉（移开）3第3页I.Internet Architecture 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 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.因特网体系结构因特网体系结构 从概念上说，因特网能够看作是域域集合。每个域由一个网络或一个相对较小互联网组成，由一个像大学、企业或政府机构那样组织负责运行。每个域是一个自主自主系统，可依据当地管理机构愿望进行配置。Internet Architecture4第4页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、甚至广域网复杂互联网组成.域建立由互联网名称与数字地址分配机构（ICANN）监管监管,Internet Architecture5第5页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 this purpose by ICANN.这是一个非赢利非赢利企业，其成立目标是协调域命名及因特网地址分配。要在因特网上建立一个域，该域必须首先经过一个得到ICANN授权授权做此工作、被称为域名注册服务商企业进行注册注册。Internet Architecture6第6页 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 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，即能够使用一个路由器连接到现有因特网上。这个路由器路由器将该域中一个网络与已经在因特网内一个网络相连接。这个特定路由器常被称为该域网关网关，因为它相当于该域通往因特网其余部分大门。Internet Architecture7第7页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 operation of the domain itself。从单个域角度看，位于其网关外面那部分因特网有时被称为“云”,这是指这是指以下事实：其网关外面因特网结构不受其控制，而且与其本身操作也没有什么关系。Internet Architecture就.而论is of+抽象n:作为表语表示主语性质或特征。意思是“含有，具备”，如：be of success=be successful be of use=be useful8第8页Any message being transmitted to a destination within the domain is 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标地任何报文都在该域内处理，传输给该域外一个目标地任何报文都首先送至网关，然后由网关向外发送到云里。Internet Architecture9第9页 If one stood at a domains gateway and looked out 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 network of gateways.一个人假如“站”在一个域网关处“向外看”云，就会发觉各种结构。确实，伴随各种域找到与云建立连接点，因特网也以有点随意有点随意方式发展着。然而，一个流行结构是，将若干域网关连接在一起，形成一个由网关组成区域网络。Internet Architecture支持/赞成，是为了.10第10页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 networks attach.In this manner,that portion of the cloud takes on a hierarchical structure(Figure 9A-I).比如，一组大学能够选择将其资源集中起来，用于构建这么一个网络。而这个区域网络接着又连接到一个更大大网络上，后者上面还连接有其它区域网络。这么，那部分云就展现出了层次结构（图9A-1）。Internet Architecture轮番地、依次11第11页II.Connecting to the lnternet To 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.II 连接到因特网连接到因特网 为了简化连接到因特网上过程，许多称为因特网服务提供商企业允许客户经过企业设备将他们域连接到因特网上，或者成为企业已经建立一个域一部分Connecting to the Internet12第12页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 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连接或许是经过暂时电话链路建立连接，这种连接称为拨号拨号连接。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一台计算机发出呼叫。这时，因特网服务提供商就为其提供因特网访问服务，连续时间为电话呼叫时间长度Connecting to the Internet13第13页 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 such as DSL,cable television lines,and satellite links.这种暂时连接模型在手机手机/手持式计算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，在位置固定应用中，暂时连接快速让位于永久连接，这种连接经过数字用户线路、有线电视线路和卫星链路等带宽带宽比较高系统建立Connecting to the Internetgive way to 让路，让步give way 让步，屈服，垮掉14第14页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 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大型机构）费用，从而使家庭用户也能够访问今天多媒体多媒体应用程序。Connecting to the Internet15第15页 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 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网络，这种网络通常实现实现为以太网总线网络。这些网络使用家里路由器访问因特网，而该路由器经过数字用户线路数字用户线路、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 Internet16第16页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.That is,each computer communicates with the router by means of a small transmitter/receiver with a range of approximately 100 feet.从而使家里系统成为因特网服务提供商建立一个域中局部网.从家中路由器到家庭局部网中计算机连接经常采取无线方式。也就是说，每台计算机使用一部作用距离大约为100英尺小型发射机发射机/接收机与路由器通信。Connecting to the Internet17第17页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.Examples 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，被用于建立热区热区。在这些热区范围内，任何含有没有线上网能力计算机（膝上型或手持式计算机）均可访问因特网。热区例子包含办公楼、网吧网吧、公共购物广场购物广场以及整个城市。Connecting to the Internet18第18页 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 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.最终，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基础结构企业。而且，它们服务普通包含为其用户提供一系列广泛硬件与软件支持。实际上，因特网服务提供商还可能提供用户所需计算资源（如数据存放和数据处理服务）中相当大相当大一部分。Connecting to the Internet比.怎么样很多19第19页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 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 two parts:III.因特网因特网编址编址 一个互联网必须与一个互联网范围编址系统相联络，该系统给系统中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实施将其扩展到128位计划。每个32位地址由两部分组成：Internet Addressing20第20页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 registered.一部分是标识计算机所在域模式，另一部分是标识域内特定计算机模式。地址中标识域那部分，即网络标识符网络标识符，是注册域时依据ICANN授权授权分配。Internet Addressing21第21页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 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 administrator or system administrator.所以，因特网中每个域是经过这个注册过程才确保拥有一个独特网络标识符。地址中标识域内特定计算机那部分叫做主机地址主机地址。主机地址由域当地管理机构（通常是含有网络管理员或系统管理员等职别人）分配。Internet Addressing 强调句22第22页 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 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地址传统上是用点分十进制记数法点分十进制记数法书写。其中，地址各字节用圆点分隔，每个字节用一个整数整数来表示，而该整数是用传统以以10为底记数法为底记数法来表示。比如，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）和其后字节00000010（用2表示）；Internet Addressing23第23页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 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（这是用二进制记二进制记数法数法书写17）、随即字节00001100（用二进制二进制书写12）以及最终字节00011001（用二进制书写25）。所以，位于艾迪生 韦斯利（Addison-Wesley）出版企业域内一台计算机可能拥有192.207.177.133这个IP地址Internet Addressing24第24页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).其中前面3个字节（192.207.177）组成网络标识符（标识Addison-Wesley这个域），最终一个字节（133）是主机地址（标识Addison-Wesley域内一台特定计算机）。Internet Addressing25第25页 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 .Note 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（即使经过使用点分十进制记数法压缩）极少能够有利于人们了解记忆。因为这个原因，每个域还分配了一个独特助记地址，称为域名。例如，艾迪生韦斯利出版企业域名是。注意这个命名系统反映了域分类，如后缀com所示,艾迪生韦斯利出版企业域属于商业性。Internet Addressing 消费、消耗；了解、记忆26第26页Such a classification 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 providers but is now used on a much broader scale.这么类别称为顶级域名顶级域名(TLD).顶级域名为数不少，包含表示教育机构机构edu、表示美国政府机构gov、表示非赢利机构org、表示博物馆museum、表示无限制使用info以及net,net最初打算用于表示因特网服务提供商，但现在使用范围要广泛得多广泛得多。Internet Addressing27第27页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.除了这些普通顶级域名之外，还有用于表示详细国家两字母顶级域名（称为国家代码国家代码顶级域名），如表示澳大利亚au和表示加拿大ca。Internet Addressing28第28页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，其当地管理机构就可自由地扩展该助记名，从而为域内计算机取得助记名。比如，位于 域内一台计算机可能被标识为。Internet Addressing29第29页 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 a hierarchical classification system.应该强调是，用于助记地址点分表示法与用于表示IP地址点分十进制记数法没相关系。相反，助记地址各部分标识计算机在一个层次分类层次分类系统中位置。Internet Addressing30第30页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 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.详细来说这个地址表示：称为ssenterprise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）。在大型域情况下，当地管理机构可能将其域分成子域。在这种情况下，域中计算机助记地址可能比较长。Internet Addressing1.把.分成。2.打断，打搅 ones thought3.闯进 the house31第31页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 computer r2d2 is in the subdomain compsc within the domain nowhereu within the class of educational domains edu.比如，假设乌有乌有大学被赋予nowhereu.edu这个域名，并选择将其域分成子域。那么，乌有大学一台计算机就可能含有像psc.nowhereu.edu这么一个地址。该地址表示：称为r2d2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 Addressing32第32页 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 to requests regarding address information.每个域当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助记地址和对应对应IP地址。这个目录在该域中充当服务器一台指定指定计算机上实现。这个服务器叫做名称服务器名称服务器，它对相关地址信息请求作出响应。Internet Addressing充当，用.形式33第33页Together,all the name servers throughout the Internet are part of an Internet-wide directory system known as the domain name system that is used to convert addresses in mnemonic form into their equivalent bit-pattern forms.整个因特网全部名称服务器一起组成一个因特网范围目录系统一部分，该系统称为域名系统，用于将助记形式地址转换成对应位模式形式。Internet Addressing组成.一部分34第34页In particular,when a human requests that a message b