What is the Internet? Where did it come from， and how did it support the growth of the World Wide Web？ What are the Internet’s 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 business， educational institutions, government agencies, and individuals together. The Internet provides around 400 million people around the world (and over 170 million people in the United States) with rvices such as e-mail, newsgroups， shopping， rearch， instant messaging， music， videos, and news. No one organization controls the Internet or how it functions， nor is it owned by anybody, yet it has provided the infrastructure for a transformation in commerce, scientific rearch， and culture. 因特网是什么? 它来自何处，和它如何支持万维网的增长? 因特网最重要的运行原则是什么?因特网是成千上万的网络和数以百万计的计算机(有时被称为主机计算机或主机)将企业、教育机构、政府机关和个人联结起来的一个互联网络。因特网为全球大约4亿人（其中美国1。7亿多人)提供诸如电子邮件、新闻讨论组、购物、研究、即时信息、音乐、视频和新闻等服务。没有任何组织控制因特网或它的运作，它也不被任何人所拥有，尽管它为商业交易、科学研究和文化提供基础设施.
鸡蛋画画The word 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 Internet’s most popular rvices， providing access to over one billion Web pages， which are documents created in a programming language called HTML and which can contain text, graphics, audio, video， and other objects， as well as “hyperlinks” that permit a ur to jump easily from one page to another. 因特网(Internet)一词起源于互联网络（internetwork）或两个或更多的计算机网络联接在一起。全球信息网,或简称万维网，是因特网上最流行的服务之一,提供对10亿多网页的访问，这些网页是由一种叫做HTML（超文本链接标示语言）编程语言生成的文件,它可以包含本文、图形、声频、视频和其他对象、以及允许用户容易地跳跃到其他网页的“超链接”. |
第二书包高辣肉8.1.1 THE EVOLUTION OF THE INTERNET 1961–2000
Internet I-today’s Internet—has evolved over the last forty years。 In this n， the Internet is not “new"; it did not happen yesterday. Although journalists and pundits talk glibly about “Internet” time—suggesting a fast—paced， nearly instant， worldwide global change mechanism, in fact， it has taken forty years of hard work to arrive at today’s Internet. 因特网I-—今天的因特网——已经发展了四十多年.在这个意义上，因特网不是“新的"，它不是昨天才发生的事。虽然新闻记者和博学家口若悬河地谈论“因特网"时代—-指一种快步调的、几乎即时的、全球性的变化机制，事实上,因特网达到今天的水平花费了四十年的艰苦努力。
The history of the Internet can be gmented into three phas. In the first pha, the Innovation Pha, 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/rver computing, and a communications protocol called TCP/IP （all described more fully below）. The original purpo of the Internet， when it was conceived in the late 1960s, was to link together large mainframe computers on college campus。 This kind of one-to-one communication between campus was previously only possible through the telephone system or postal mail。 因特网的历史可以划分为三个阶段。在第一阶段即发明阶段，从1961年到1974年，因特网的基本构建模块被概念化并随之用真正的硬件和软件实现。其基本的构建模块是:分组交换硬件、客户机/服务器计算技术和一个被称为传输控制协议的通信协议（它们都将在后文进行全面描述）。当在20世纪60年代末期构思的时候，因特网最初的目的是将大学校园内的大型计算机联结起来。在校园之间这种一对一的通信先前只有经过电话系统或邮政邮件才可能进行。
In the cond pha, the Institutional Pha， from 1975 to 1995， large institutions such as the Department of Defen 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 veral government-supported demonstration projects, the Department of Defen contributed a million 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 Rearch Projects Agency Network）. In 1986, the National Science Foundation assumed responsibility for the development of a civilian Internet （then called NSFNet) and began a ten-year—long $200 million expansion program。 在第二阶段即机构化阶段，从1975年到1995年，像国防部和国家科学基金委等一些大机构为这项被称为因特网的刚刚起步的发明提供资金并使其合法化。当因特网的概念在一些政府支持的示范性项目中被证实后，国防部提供了一百万美元资金将这个概念和示范性项目发展成为一个可以承受核战的军事通信系统。这个努力产生了以后被称作ARPANET的东西（高级研究计划局建立的计算机网)。在1986年，国家科学基金委承担了建立民用因特网的任务(那时叫做NSFNet），并且开始了为期十年、耗资2亿美元的扩展计划。 In the third pha, the Commercialization Pha， from 1995–2001， government agencies encouraged private corporations to take over and expand both the Internet backbone and local rvice to ordinary citizens—families and individuals across America and the world who were not students on campus. By 2000， the Internet's u had expanded well beyond military installations and rearch universities. 在第三阶段即商业化阶段，从1995年至2001年，政府机构鼓励私营公司接管并扩展因特网主干和接管为普通市民提供的地方性服务，普通市民包括在全美国和全世界的家庭以及非在校学生等个体.到2000年，因特网的应用已大大超出了军事设备和大学研究的范围。 |
8.1。2 THE INTERNET: KEY TECHNOLOGY CONCEPTS
In 1995, the Federal Networking Council (FNC) took the step of passing a resolution formally defining the term Internet。 “Internet" refers to the global information system that— 1.is logically linked together by a globally unique address space bad on the Internet Protocol （IP） or its subquent extensions/follow—ons;在 1995 年，联邦的网络委员会（FNC)通过了一个关于因特网术语正式定义的决议。 “因特网"是这样的全球信息系统——1. 通过以因特网协议或其扩展或继续为基础的、独特的地址空间被逻辑性地联结起来；
II。 is able to support communications using the Transmission Control Protocol/Internet Protocol (TCP/IP） suite or its subquent extensions/follow-ons， and/or other IP—compatible protocols; and III。 provides， us or makes accessible， either publicly or privately， high level rvices layered on the communications and related infrastructure described herein. II.能够支持使用TCP/IP（传输控制协议/因特网协议）组或其扩展/继续、和/或其他与IP协议（因特网协议）兼容的协议进行的通信；并且 III。提供、使用或使可访问此处描述的通信及其相关基础设施（不论公用的还是专用的）上分层次的高水平服务。
Bad on the definition， the Internet means a network that us the IP addressing scheme, supports the Transmission Control Protocol （TCP）， and makes rvices available to urs much like a telephone system makes voice and data rvices available to the public2. 基于这个定义，因特网表示这样一个网络——使用IP地址分配方案、支持传输控制协议，并使用户可以使用多种服务——与电话系统使公众能够使用声音和数据服务非常类似。
Behind 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/rver computing3。 Although the Internet has evolved and changed dramatically in the last 30 years, the three concepts are at the core of how the Internet functions today and are the foundation for Internet II. 在这个正式的定义背后，隐含着三个极其重要的概念:分组交换、TCP/IP(传输控制协议/网际协议）通信协议和客户机/服务器计算技术，它们乃是理解因特网的基础。尽管因特网在过去30年发生了引人注目的进化和变化，但这三个概念仍是今天因特网运转的核心，也是因特网II的基础。
Packet Switching. Packet switching is a method of slicing digital messages into parcels called “packets，" nding the packets along different communication paths as they become available, and then reasmbling the packets once they arrive at their destination. Prior to the development of packet switching， early computer networks ud lead, dedicated telephone circuits to communicate with terminals and other computers。 In circuit-switched networks such as the telephone system, a complete point—to—point circuit is put together, and then communication can proceed。 分组交换。分组交换是传输数据的一种方法，它先将数据信息分割成许多称为“分组”的数据信息包；当路径可用时，经过不同的通信路径发送；当到达目的地后,再将它们组装起来。在分组交换发展之前，早期计算机网络使用租用的专用电话线路和终端与其他计算机进行通信。在线路交换网络如电话系统中，一个完全点对点的线路被连结在一起,然后才能进行通信.
However, the “dedicated” circuit-switching techniques were expensive and wasted available communications capacity—the circuit would be maintained regardless of whether any data was being nt. For nearly 70％ of the time， a dedicated voice circuit is not being fully ud becau of paus between words and delays in asmbling the circuit gments， both of which incread the length of time required to find and connect circuits。 A better technology was needed. 然而，这些“专用的”线路交换技术既价格昂贵又浪费有效的通信能力——不论是否有数据输送都需要维持线路。由于字间的停顿和组装时的延迟，一条专用的声音线路在几乎70%的时间内没有得到充分利用,而这两种因素都增加寻找和连接线路所需的时间长度。因此需要一种比较好的技术。
The first book on packet switching was written by Leonard Kleinrock in 1964， and the technique was further developed by others in the defen rearch labs of both the United States and England。 With packet switching, the communications capacity of a network can be incread by a factor of 100 or more。 The communications capacity of a digital network is measured in terms of bits per cond。 Imagine if the gas mileage of your car went from 15 miles per gallon to 1,500 miles per gallon—all without changing too much of the car! 第一本关于分组交换的著作是由Leonard Kleinrock于1964年所著,美国和英国防卫研究实验室的其他研究人员使这项技术得到进一步发展.由于使用分组交换技术，网络的通信能力提高了100倍甚至更多。数字网络的通信能力用每秒位来衡量。想象一下汽车行驶的里程，从每加仑汽油行驶15里提高到每加仑汽油行驶1500 里——而汽车没有太大的改变!
In 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 destination address, as well as quencing information and error control information for the packet。 Rather than being nt directly to the destination address, in a packet network, the packets travel from computer to computer until they reach their destination. The computers are called routers。 Routers are special purpo 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 u computer programs called routing algorithms. 在分组交换的网络中，信息首先被分解为许多信息包。每个信息包附加数字代码用于指示其源地址（开始点）和目的地地址、以及顺序信息和错误控制信息.在分组网络中，信息包不是直接被送到目的地地址,而是在计算机与计算机之间旅行直到它们到达目的地。这些计算机叫做路由器。路由器是一种特殊用途的计算机，它将组成因特网的成千上万个不同计算机网络互相联接起来，并在信息包旅行时将它们的向终极目的地发送。路由器使用一种叫做路由算法的计算机程序,以确保信息包取通向它们目的地的最佳可用路径。
Packet switching does not require a dedicated circuit but can make u of any spare capacity that is available on any of veral hundred circuits. Packet switching makes nearly full u of almost all available communication lines and capacity。 Moreover， if some lines are disabled or too busy, the packets can be nt on any available line that eventually leads to the destination point. 分组交换不需要一个专用线路,但是可以利用几百条线路中任何可用的空闲能力。分组交换几乎充分利用了所有可用的通信线路和能力。而且，如果一些线路不通或太忙的话，信息包能在任何可用的、最终通向目的地的线路上传送.
TCP/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 reasmbling them into a coherent message。 This was like having a system for producing stamps， but no postal system （a ries of post offices and a t of address). TCP/IP.尽管分组交换是通信能力的一个巨大进步,但对于将数字信息分解为信息包、将它们传输到适当的地址， 然后重新组装为原来的信息,还没有一种公认的方法。这就像有了一个生产邮票的系统，而没有邮政系统(一系列的邮局和一套住址)一样.
TCP/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 is a t 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 nding and/or receiving messages。 Protocols can be implemented in either hardware or software. TCP/IP is implemented in Web software called rver software （described below）. TCP is the agreed upon protocol for transmitting data packets over the Web. TCP establishes the connections among nding and receiving Web computers， handles the asmbly of packets at the point of transmission， and their reasmbly at the receiving end. TCP/IP回答了在因特网上用信息包做什么和如何处理信息包的问题。TCP指传输控制协议,IP表示网际协议。协议是一组用于信息的格式化、次序化、压缩和检查错误的规则.它也可以限定传输速度和网上设备显示它们已停止发送及(或)接收信息的方法。协议既可以通过硬件也可通过软件来实现。TCP/IP（传输控制协议/网际协议)通过被称为服务器软件的网络软件来实现（在下文描述）。TCP(传输控制协议）是用来在网上传输数据的公认协议.TCP(传输控制协议）在发送和接收网络计算机之间建立连接，处理信息包在传输点的组装和在接收端的重新组装。
TCP/IP is divided into four parate 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 other network technology。 TCP/IP(传输控制协议/网际协议)被分为四个独立的层，由每层处理通信问题的一个不同方面。网络接口层负责信息包在网络媒体上的排列和接收,网络媒体可能是局域网（以太网)、令牌环形网或其他网络技术.
TCP/IP is independent from 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 quencing the packets to and from the application。 The Application Layer provides a wide variety of applications with the ability to access the rvices of the lower layers. Some of the best known applications are Hyper Text Transfer Protocol (HTTP）, File Transfer Protocol （FTP)， and Simple Mail Transfer Protocol （SMTP)， all of which we will discuss later in this chapter. TCP/IP(传输控制协议/网际协议）独立于任何局部网络技术，并能适应在局部水平上的改变。因特网层负责信息的寻址、封装及其在因特网上的路线排定。通过对信息包去与来应用层的确认和排序，传送层负责为应用层提供通信。应用层为许多应用提供访问较低层服务的能力。一些众所周知的应用是超文本传输协议（HTTP)、文件传输协议(FTP）和简单邮件传输协议（SMTP)，稍后我们将本章中讨论。IP Address。 TCP handles the packetizing and routing of Internet messages。 IP provides the Internet’s addressing scheme。 Every computer connected to the Internet must be assigned an address—otherwi it cannot nd or receive TCP packets. For instance, when you sign onto the Internet using a dial—up telephone modem， your computer is assigned a temporary address by your Internet Service Provider。 IP地址.TCP(传输控制协议）处理因特网信息的分组化和传输路线排定。IP(网际协议）提供因特网的地址分配方案.每部连接到因特网的计算机必须分配一个地址,否则它不能够发送或接受TCP（传输控制协议)信息包。举例来说，当你在使用调制解调器拨号上网时，你的计算机由因特网服务提供商分配一个临时地址。
广州医保电话Internet address, known as IP address， are 32-bit numbers that appear as a ries of four parate numbers marked off by periods, such as 201.61.186。227. Each of the four numbers can range from 0–255. This “dotted quad” addressing scheme contains up to 4 billion address （232）。 The leftmost number typically indicates the network address of the computer， while remaining numbers help to identify the specific computer within the group that is nding （or receiving ） a message. 因特网地址,即众所周知的IP地址，是一个32位的数字，它以一串由园点隔开的四个数字出现,例如 201。61.186.227。四个数字中的每一个都在0—255范围内。这个“点分四元组"地址分配方案包含多达到40亿个地址(232)。最左边的那个数字指示计算机的网络地址,而其余的数字帮助识别正在发送(或接收）信息的团体里面一台特定的计算机。
The current version of IP is called Version 4， or IPv4。 Becau many large corporate and government domains have been given millions of IP address each (to accommodate their current and future work forces)， and with all the new networks and new Internet—enabled devices requiring unique IP address being attached to the Internet, a new version of the IP protocol， called IPv6 is being adopted。 This scheme contains 128—bit address, or about one quadrillion （1015). IP现在版本叫做第4版,或IPv4.因为许多大公司和政府在各自的域中已给定了数百万个IP地址（以适应他们当前和未来的劳动力)，且由于新网络和新的可上网设备需要独特的IP地址,新版本IP协议IPv6正在得到采用。这个方案包含128位的地址,或曰大约1015个地址。
Domain Names and URLs. Most people cannot remember 32-bit numbers。 IP address can be reprented by a natural language convention called domain names. The domain name system (DNS） allows expressions such to stand for numeric IP address （'s numeric IP is 216.200.247.134）。 Uniform resource locators （URLs）， which are the address ud by Web browrs to identify the location of content on the Web, also u domain names as part of the URL。 A typical URL contains the protocol to be ud when accessing the address, followed by its location。 域名和统一资源定位(URL)。大多数人记不住32位的数字。IP地址可由一个自然语言约定（称为域名）来表示。域名系统(DNS)允许像cnet。com这样的表达代表数值型IP地址( 的数值型IP地址是(216。200.247.134)。统一的资源定位是网络浏览器用于识别网上内容位置的地址,也使用域名作为它的一部分。一个典型的网址包含访问地址时使用的协议,接着是它的位置。
Client/Server Computing。 While packet switching exploded the available communications capacity and TCP/IP provided the communications rules and regulations， it took a revolution in computing to bring about today’s Internet and the Web. That revolution is called client/rver computing and without it, the Web—in all its richness—would not exist. In fact, the Internet is a giant example of client/rver computing in which over 70 million host rver computers store Web pages and other content that can be easily accesd by nearly a million local area networks and hundreds of millions of client machines worldwide. 客户机/服务器计算技术。虽然分组交换使有效的通信能力激增，且TCP/IP协议提供了通信规则，在计算机技术中,发生了又一次革命才造就了今天的因特网和万维网。这次革命叫做客户机/服务器计算技术，没有它，万维网及其丰富信息将不会存在。事实上，因特网是客户机/服务器计算技术的一个巨大实例,其中,超过7000万部主机服务器计算机储存网页和其他内容,这些网页和内容能被全世界接近一百万个局域网和数亿台客户机容易地访问。
Client/rver computing is a model of computing in which very powerful personal computers called clients are connected together in a network together with one or more rver computers。 The clients are sufficiently powerful to accomplish complex tasks such as displaying rich graphics， storing large files, and processing graphics and sound files， all on a local desktop or handheld device。 Servers are networked computers dedicated to common functions that the client machines on the network need， such as storing files, software applications, utility programs such as Web connections, and printers. 客户机/服务器计算技术是一种计算模型，其中相当多台被称为客户机的个人计算机联结在一起并与一台或更多的服务器计算机联结在一个网络中。这些客户机功能足够强大以完成复杂的任务如显示丰富的图形、储存大型文件、并处理图形和声音文件,这些任务全部在当地的台式或手持式装置上完成。服务器是联网的计算机，专门用于提供客户机在网上需要的公共功能,例如储存文件、软件应用、公用程序如网络连接、和打印。
To appreciate what client/rver computing makes possible， you must understand what preceded it. In the mainframe computing environment of the 1960s and 1970s, computing power was very expensive and limited。 For instance, the largest commercial mainframes of the late 1960s had 128k of RAM and 10 megabyte disk drives， and occupied hundreds of square feet. There was insufficient computing capacity to support graphics or color in text documents, let alone sound files or hyper linked documents and databas。 为了充分理解客户机/服务器计算技术的作用，你必须了解在它之前的东西.在20世纪60年代和70年代的大型计算机环境中，计算机能力非常昂贵而有限。比如,60年后期最大的商业化大型机有128K随机存取存储器和10兆磁盘驱动器，而且占据数百平方英尺空间.计算能力不足以支持图形和文本中的颜色，更不用说声音文件或超链接文档和数据库。
With the development of personal computers and local area networks during the late 1970s and early 1980s， client/rver computing became possible. Client/rver computing has many advantages over centralized mainframe computing。 For instance, it is easy to expand capacity by adding rvers and clients. Also， client/ rver networks are less vulnerable than centralized computing architectures. If one rver goes down， backup or mirror rvers can pick up the slack; if a client machine is inoperable， the rest of the network continues operating. Moreover， processing load is balanced over many powerful smaller machines rather than being concentrated in a single huge machine that performs processing for everyone。 Both software and hardware in client/rver environments can be built more simply and economically. 20世纪70年代后期和80年代初期，随着个人计算机和局域网的发展,客户机/服务器计算技术成为可能。客户机/服务器计算技术比中央大型机计算有许多优势。比如，通过增加服务器和客户机，可很容易地扩容。同时,客户机/服务器网络比中央计算结构不易受损。如果一个服务器被破坏，备用的或镜像服务器能恢复工作；如果一部客户机不能运转，网络的其部分可继续运行。而且, 负荷处理通过许多强大的、较小的机器达到平衡，而不是集中于一部为每个人进行处理的巨型机。在客户机/服务器环境中，建立软件与硬件都更简单、更经济.
Today there are about 450 million PCs in existence worldwide。 Most of the PCs can display and process graphics， sound files， and colored text。 They have memories up to 512MB， 20 gigabyte hard drives, and occupy about two square feet。 The personal “supercomputers,” when tied together in local area networks or into large wide area networks such as the Web， make it possible for millions of people to enjoy “rich” Web documents and experiences. Soon the capabilities will move to handheld devices such as the Palms and HP Jornada， and wireless cell phones （much “thinner clients"）。 In the process, more computer processing will be performed by central rvers （reminiscent of mainframe computers of the past). 今天全世界大约有4.5亿台个人计算机，其中大多数可以显示并且处理图形、声音文件、和彩色文本。他们具有高达512MB内存、20G（兆字节）硬盘驱动器，而大约只占2平方英尺空间。这些个人的“超级计算机"，把它们联结起来接入局域网或大型广域网如因特网，使数以百万计的人们享受“丰富的"网络文件和经验成为可能。这些能力将很快会移植到如Palms、HP Jornada和无线蜂窝电话等手持式装置中（很多“瘦客户机”)。在这个过程中，更多的计算机处理将由中央服务器完成（过去的大型计算机的遗风）。 |
