Telecommunications enables people to send and receive personal messages across town, between countries, and to and from outer space. It also provides the key medium for news, data, information and entertainment.
When a signal reaches its destination, the device on the receiving end converts the electronic signal back into an understandable message, such as sound over a telephone, moving images on a television, or words and pictures on a computer screen. 电信使世界各地的人们得以互相联系，即刻获 取信息，并从边远地区实施通信。电信通常涉及一个信息发送者和一个或多个接收者，他们通过电话系统等把信息从一地发送到另一地的技术相联系。电信设备将不同类型的信息，如声音和图像，转换成电子信号。然后，这些信号就可以通过电话 线或无线电波等媒介进行发送。信号到达目的地后，接收端的设备将电子信号转换 回可以理解的信息，如电话中的声音、电视上的活动图像或计算机屏幕上的文字和 图片。电信使人们能够在城镇不同地方、国家之间以及向外层空间和从外层空间发送和接收个人信息。电信也为新闻、数据、信息和娱乐提供了关键的媒介。
Telecommunications messages can be sent in a variety of ways and by a wide range of devices. The messages can be sent from one sender to a single receiver (point-to-point) or from one sender to many receivers (point-to-multipoint). Personal communications, such as a telephone conversation between two people or a facsimile (fax) message, usually involve point-to-point transmission. Point-to-multipoint telecommunications, often called broadcasts, provide the basis for commercial radio and television programming.
电信信息可通过各种方式和设备发送。信息可由一个发送者发送给一个接收者（点对点）， 或者由一个发送者发送给多个接收者（点对多点）。个人通信，如两个人之间的电话对话或传真信息，通常涉及点对点的传输。通常称为广播的点对多点电信传输，为商业无线电和电视节目播送提供了基础。
Telecommunications begin with messages that are converted into electronic signals. The signals are then sent over a medium to a receiver, where they are decoded back into a form that the person receiving the message can understand. There are a variety of ways to create and decode signals, and many different ways to transmit signals.
电信以信息转换为电子信号为 开端。然后，这些信号通过媒介发送到接收机，并在那里解码，恢复为接收信息的 人能够理解的形式。有各种方法可以生成并解译信号，也有许多不同方法可以传输 信号。
Devices such as the telegraph and telephone relay messages by creating modulated electrical impulses, or impulses that change in a systematic way. These impulses are then sent by wires, radio waves, or other media to a receiver that decodes the modulation.
电报机与电话机等设备，通过生成调制电脉冲或以系统化方式变化的脉冲，来传递信息。接下来，这些脉冲通过导线、无线电波或其他媒介发送给接收机，并由其进行解调。
The telegraph, the earliest method of delivering telecommunications, works by converting the contacts (connections between two conductors that permit a
flow of current) between a telegraph key and a metal conductor into electrical impulses.hese impulses are sent along a wire to a receiver, which converts the impulses into short and long bursts of sound or into dots and dashes on a simple printing device.
电报机是最早的传递电信信息的方法，它通过将电报电键与金属导 体之间的接触（使电流得以流动的两个导体之间的连接）转换成电脉冲而进行工 作。这些脉冲沿着导线发送到接收机，而接收机则将这些脉冲转换成长与短的声音脉冲串，或者在简单的打印设备上打印出来的点与划。
T Specific sequences of dots and dashes represent letters of the alphabet. In the early days of the telegraph, these sequences were decoded by telegraph operators. In this way, telegraph operators could transmit and receive letters that spelled words. Later versions of the telegraph could decipher letters and numbers automatically. Telegraphs have been largely replaced by other forms of telecommunications, such as fax machines and electronic mail (e-mail), but they are still used in some parts of the world to send messages.
特定的点与划序列代表字母 表中的字母。在早期的电报中，这些序列由电报机操作员进行解译。这样，电报机 操作员就可以发送和接收可拼成词语的字母。后来的电报机能自动解译字母和数 字。电报机在很大程度上已被其他的电信形式所取代，如传真机和电子邮件，但在 世界有些地方，电报机仍然用来发送信息。
Telegraphs, telephones, radio, and television all work by modifying electronic signals, making the signals imitate, or reproduce, the original message. This form
of transmission is known as analog transmission. Computers and other types of electronic equipment, however, transmit digital information.
电报机、电话机、无线电和电视都是通过修改电子信号，使其模拟或再现原来的信息，来进行工作的。这种传输称为模拟传输。然而，计算机和其他类型的电子设备是传输数字信号的。数字技术将信息转换成电子形式。其方法首先是多次测量信息的不同特性，如语音的音高和音量。
Digital technologies convert a message into electronic form first by measuring different qualities of the message, such as the pitch and volume of a voice, many times. These measurements are then encoded into multiple series of binary numbers, or 1s and 0s.
数字技术将信息转换成电子的形式。其方法首先是多次测量信息的不同特性，如语音的音高和音量。然后，这些测量值被编译成多个系列的二进制数或1与0。
Finally, digital technologies create and send electrical impulses that correspond to the series of 1s and 0s. Digital information can be transmitted faster and more clearly than analog signals, because the electrical impulses only need to correspond to two digits and not to the full range of qualities that compose the original message, such as the pitch and volume of a human voice.
最后，数字技术生成并发送与这些系列的1和0相对应的电脉冲。与模拟信号比较起来，数字信息可以更快、更清晰地传输，因为电脉冲仅需与两个数字对应，而不是构成原信息的所有特性，如人的说话声的音高和音量。
While digital transmissions can be sent over wires, cables or radio waves, they must be decoded by a digital receiver. New digital telephones and televisions are being developed to make telecommunications more efficient.
数字传输可以通过导线、电缆或无线电波发送，但必须由数字接收机进行解译。新型数字电话和电视正在开发中，以提高电信的效率。
Most personal computers communicate with each other and with larger networks, such as the Internet, by using the ordinary telephone network. Since the telephone network functions by converting sound into electronic signals, the computer must first convert its digital data into sound. Computers do this with a device called a modem, which is short for modulator/demodulator.
大多数个人计算机通过使用普通电话网，来进行彼此间的和与因特网等大型网络的通信。因为电话网是通过将语音信号转换成电子信号来工作的，计算机必须首先将其数字数据转换成语音信号。计算机使用被称为调制解调器的设备完成这项工作。调制解调器是调制器/解调器的缩略。
A modem converts the stream of 1s and 0s from a computer into an analog signal that can then be transmitted over the telephone network, as a speaker’s voice would. The modem of the receiving computer demodulates the analog sound signal back into a digital form that the computer can understand.
调制解调器将计算机输出的1和0的数字流转换成模拟信号，而模拟信号可随后通过电话网传输，就像通话者的声音那样。接收端的计算机的调制解调器将模拟语音信号解调
还原为计算机能理解的数字形式。
Telecommunications systems deliver messages using a number of different transmission media, including copper wires, fiber-optic cables, communication satellites, and microwave radio. One way to categorize telecommunications media is to consider whether or not the media uses wires.
电信系统传输信息，使用的是许多不同的传输媒介，包括铜线、光缆、通信卫星和微波。划分电信媒介的一种方法是看媒介是否使用导线。
Wire-based (or wireline) telecommunications provide the initial link between most telephones and the telephone network, and are a reliable means for transmitting messages.
基于导线（或有线）的电信提供了大多数电话与电话网之间的初期链路，是一种可靠的信息传输方式。
Telecommunications without wires, commonly referred to as wireless communications, use technologies such as cordless telephones, cellular radio telephones, walkie-talkies, citizens band (CB) radios, pagers, and satellites. Wireless communications offer increased mobility and flexibility.
无线电信，通常称作无线通信，使用无绳电话、蜂窝式无线电话、步话机、民用波段无线电台、寻呼机和卫星等技术。无线通信提供了更高的机动性和灵活性。
Individual people, businesses, and governments use many different types of telecommunications systems. Some systems, like the telephone system, use a network of cables, wires, and switching stations for point-to-point communication.
个人，商业和使用不用方式的通讯系统。有些系统，如电话系统，使用由电缆、导线和交换台组成的网络，来进行点对点的通信。
Other systems, such as radio and television, broadcast signals through space, which can be received by anyone who has a device to receive them. For example, a telephone call may travel by means of copper wire, fiber-optic cable, and radio waves as the call is sent from sender to receiver. All telecommunications systems are constantly evolving as telecommunications technology improves.
其他系统，如无线电台与电视台，通过空间来播出信号，任何拥有接收设备的人都可以接收。例如，当我们打电话的时候，电话可以通过铜线，光缆和无线电波从发送人传送到接收人。随着通信科技的提升，通信系统也在不断地进步。
Computer telecommunications, with the ability to send and receive audio, video, text, software, and multimedia, is one of the fastest-growing segments of the telecommunications market.
计算机远程通信具有发送和接收音频信号、视频信号、文本、软件和多媒体的能力，是电信市场发展最快的部分之一。
Computer telecommunications takes advantage of existing telephone
connections to transmit digital data. This type of transmission is frequently done over the Internet, a decentralized network of personal, business, government, educational computers, and sources of information.
计算机远程通信利用现有的电话连接来传输数字数据。这种传输常常通过因特网进行，而因特网是一个由个人、工商企业、和教育机构所用的计算机以及信息源构成的分散式网络。
Some computers connect directly to the digital portion of the telephone network using the Integrated Services Digital Network (ISDN), but this requires the installation of special devices and telephone line conditioning. An improved modem system for regular phone lines, called Digital Subscriber Line (DSL), is being developed to increase modem speed tremendously.
有些计算机使用综合业务数字网直接连接到电话网的数字部分，但是这需要安装专用设备和进行电话线调整。为了大幅度提高调制解调器的速率，目前正在开发一种供常规电话线使用的改进型调制解调器系统，称为数字用户线路。
Electronic mail, or e-mail, is a key attraction of the Internet and a common form of computer telecommunications. E-mail is a text-based message delivery system that allows information such as typed messages and multimedia to be sent to individual computer users. Local e-mail messages (within a building or a company) typically reach addressees by traveling through wire-based internal networks.
电子邮件是因特网吸引人的一个亮点，也是计算机远程通信的常见形式。电子邮件是基于文本的信息传输系统，它能将键入的信息和多媒体信息等发送给个人计算机用户。（一幢建筑或一家公司内的）本地电子邮件通常经由基于导线的内部网传送给收件人。
E-mail that must travel across town or across a country to reach the final destination usually travels through the telephone network. Other computer telecommunications technologies that businesses frequently use include automated banking terminals and devices for credit card transactions that bill charges directly to a customer’s bank account.
必须横穿城市或国家才能到达最终目的地的电子邮件，通常通过电话网进行传输。工商企业经常使用的其他计算机远程通信技术包括自动银行终端和设备，用来处理将费用直接从顾客银行帐户上扣除的信用卡业务。
Personal computers have pushed the limits of the telephone system as more and more complex computer messages are being sent over telephone lines, and at rapidly increasing speeds. This need for speed has encouraged the development of digital transmission technology.
随着越来越复杂的计算机信息以快速增长的速度通过电话线发送，个人计算机拓展了电话系统的作用范围。提高速度的需要促进了数字传输技术的发展。
Innovations in fiber-optic technology will hopefully keep up with the growing use of personal computers for telecommunications. The next generation of cellular telephones, pagers, and televisions will also benefit from the speed and clarity of
digital telecommunications.
光纤技术的革新有望跟上个人计算机在远程通信方面不断增长的使用。下一代蜂窝电话、寻呼机和电视机也将受益于数字远程通信的速度和清晰度。
Telecommunications and information technologies are merging and converging. This means that many of the devices that we associate with only one function may evolve into more versatile equipment. This convergence is already happening in various fields.
电信和信息技术正在融合。这就意味着，我们只将其与一种功能联系起来的设备，许多可能演变为具有更多用途的设备。这种融合已经开始在各种不同的领域发生。
Some telephones and pagers are able to store not only phone numbers but also names and personal information about callers. Advanced phones with keyboards and small screens are now in development that can access the Internet and send and receive e-mail.
有些电话机和寻呼机不但能储存电话号码，而且还能储存呼叫者的姓名和个人信息。现在正在研制带有键盘和小屏幕的先进电话机，可以访问因特网和发送与接收电子邮件。
Personal computers can now access information and video entertainment and are in effect becoming a combined television set and computer terminal. Television sets, which we currently associate with broadcast and cable-delivered video programming, are able to gain access to the Internet through add-on
appliances.
个人计算机现在能访问信息和视频娱乐节目，实际上正在成为电视机和计算机终端的组合体。我们当前将其与广播和电缆传输的视频节目联系在一起的电视机，能够通过附加的设备访问因特网。
Future modifications and technology innovations may blur the distinctions between appliances even more. 未来的改进和技术革新可能会使设备之间的区别进一步模糊化。
Convergence of telecommunications technologies will also trigger a change in the content available and the composition of the content provider. Both television and personal computers will be incorporating new multimedia, interactive, and digital features.
电信技术的融合也将在可获得的内容以及内容供应商的构成方面引起改变。电视机和个人计算机都将不断地吸纳新的多媒体、交互和数字化特征。
For example, an entertainment program might have on-screen pointers to World Wide Web pages containing more information about the actors. In the near term, before the actualization of a fully digital telecommunications world, devices like modems will still be necessary to provide an essential link between the old analog world and the upcoming digital one.
例如，娱乐节目可能会有屏幕指示，链接到万维网上包含更多演员信息的网页。从近
期来看，在全数字化电信时代到来之前，调制解调器等设备在为旧的模拟世界与即将到来的数字世界提供基本链接方面，仍然必不可少。
第八单元
The need to share information and resources among different computers has led to linked computer systems, called networks, in which computers are connected so that data can be
transferred from machine to machine. In these networks, computer users can exchange messages and share resources such as printing capabilities, software packages, and data storage facilities-that are scattered throughout the system. The underlying software required to support such applications has grown from simple utility packages into an expanding system of network
software that provides a sophisticated network wide infrastructure.
In a sense, network software is evolving into a network wide operating system.
在不同计算机之间共享信息和资源的需要，导致了相互连接的计算机系统的产生。这种相互连接的计算机系统被称为网络。在网络中，计算机连接在一起，从而数据可以从一台计算机传输到另一台计算机。在网络中，计算机用户可以交换信息，并共享分散在整个网络系统的资源，如打印能力、软件包以及数据存储设备。支持这类应用所需的基本软件，已经从简单的实用软件包发展成一个不断扩展的网络软件系统，该系统提供了一个复杂的
网络范围的基础结构。从某种意义上说，网络软件正在演变成一个网络范围的操作系统。
Network Classifications 网络分类
A computer network is often classified as being either a local area network (LAN) , a metropolitan area network (MAN), or a wide area network (WAN). A LAN normally consists of a collection of computers in a single building or building complex. For example, the computers on a university campus or those in a manufacturing plant might be connected by a LAN. A MAN is a network of intermediate size, such as one spanning a local community. A WAN links machines over a greater distance-perhaps in neighboring cities or on opposite sides of the world.
计算机网络常常划分为局域网、城域网和广域网。局域网通常由一幢建筑物或一个建筑群中的若干计算机组成。例如，大学校园里的计算机或制造工厂中的计算机可以用局域网连接。城域网属于中型网络，如一个覆盖某一社区的网络。广域网连接地理范围更广的计算机，这些计算机或许在相邻的城市，或许在地球相反的两面。（ complex n 综合体，集合体）
Another means of classifying networks is based on whether the network’s internal operation is based on designs that are in the public domain or on innovations owned and controlled by a particular entity such as an individual or a corporation. A network of the former type is called an open network; a network of the latter type is called a closed, or sometimes a proprietary network.
网络分类的另一种方式是根据网络的内部运行是基于无专利权保护的设计还是基于特定实体（如个人或公司）所拥有和控制的革新。前一种类型的网络称为开放式网络，后一种类型的网络称为封闭式网络，有时也称为专有网络。
The Internet is an open system. In particular, communication throughout the Internet is governed by an open collection of standards known as the TCP/IP protocol suite. Anyone is free to use these standards without paying fees or signing license agreements. In contrast, a company such as Novell Inc. might develop systems for which it chooses to maintain ownership rights, allowing the company to draw income from selling or leasing these products. Networks based on such systems are examples of closed networks.
因特网属于开放式系统。尤其是，整个因特网的通信是由一组称为TCP/IP协议组的开放标准来控制的。任何人都可以自由地使用这些标准，而不需要付费或签署许可协议。相反，像Novell股份有限公司这样的公司可能选择为其开发的系统保留所有权，通过出售或出租这些产品获得收入。基于这类系统的网络属于封闭式网络的例子。
Still another way of classifying networks is based on the topology of the network, which refers to the pattern in which the machines are connected. The bus topology, ring topology, and star topology are three popular topologies. Of these, the star network is perhaps the oldest, having evolved from the paradigm of a large central computer serving many users. As the simple terminals employed by these users grew into small computers themselves, a star network emerged. A point to emphasize is that the connections between machines in a network do not need to be physical. Wireless networks, using radio broadcast technology, are
becoming quite common.
还有一种网络分类方法，它基于网络的拓扑结构，即计算机相互连接的模式。总线拓扑结构、环形拓扑结构和星形拓扑结构是3种流行的拓扑结构。其中，星形网络或许是最古老的，这种网络由一台大型计算机服务许多用户的范式演变而来。随着这些用户所使用的简单终端本身发展成小型计算机，星形网络也就出现了。需要强调的一点是，在一个网络中，计算机之间的连接并不一定是物理连接。使用无线广播技术的无线网络正在变得相当常见。
For a network to function reliably, it is important to establish rules by which network activities are conducted. Such rules are called protocols. By developing and adopting protocol standards, venders are able to build products for network applications that are compatible with products from other venders. Thus, the development of protocol standards is an indispensable process in the development of networking technologies
为了网络可靠运行，确立进行网络活动所遵循的规则很重要。这类规则称为协议。通过开发和采用协议标准，不同厂商制造的网络应用产品能够相互兼容。因此，在联网技术的开发中，协议标准的开发是一个必不可少的过程。
As an introduction to the protocol concept, let us consider the problem of coordinating the transmission of messages among computers in a network. Without rules governing this communication, all the computers might insist on transmitting messages at the same time or might fail to relay messages when that assistance is required.
作为对协议概念的介绍，让我们考虑在一个网络的计算机之间协调报文传输的问题。如果没有控制这种通信的规则，所有的计算机就可能坚持同时传输报文，或者在需要传递报文时而未能传递。
One approach to solving this problem is the token ring protocol, which was developed by IBM in the 1970s and continues to be a popular protocol in networks based on the ring topology
解决这个问题的一种方法是令牌环协议，该协议由IBM公司20世纪70年代开发，今天在基于环形拓扑结构的网络中依然是一种很流行的协议。
In this protocol, all the machines in the network transmit messages in only one common direction, meaning that all messages sent over the network move around the ring in the same direction by being forwarded from computer to computer. When a message reaches its destination, the destination machine keeps a copy of it and forwards a copy on around the ring. When the forwarded copy reaches the originating computer, that machine knows that the message must have reached its destination and removes the message from the ring. Of course, this system depends on inter-machine cooperation. If a machine insists on constantly transmitting messages of its own rather than forwarding those of the other machines, nothing will be accomplished.
在这个协议里，网络中的所有计算机都只沿一个共同的方向传输报文（图8A-1）。也就是说，通过网络发送的所有报文都沿一个相同的方向绕环形网络移动，依次经由各个计算机转发。一份报文到达目的地后，目的地的计算机保留一个副本并绕环形网络转发一个
副本。当转发的副本到达始发计算机时，该计算机知道报文一定到达了目的地，并将其移出环形网络。当然，这种系统的运行依靠计算机之间的合作。如果一台计算机坚持不断地传输自己的报文，而不转发其他计算机的报文，那么这个系统就什么也执行不了。
To solve this problem, a unique bit pattern, called a token, is passed around the ring. Possession of this token gives a machine the authority to transmit its own message; without the token, a machine is only allowed to forward messages. Normally, each machine merely relays the token in the same manner in which it relays messages. If, however, the machine receiving the token has messages of its own to introduce to the network, it transmits one message while holding the token. When this message has completed its cycle around the ring, the machine forwards the token to the next machine in the ring. Likewise, when the next machine receives the token, it can either forward the token immediately or transmit its own new message before sending the token on to next machine. In this manner, each machine in the network has equal opportunity to introduce messages of its own as the token circles around the ring.
为了解决这个问题，在环形网络中传递一个称为令牌的独特位模式。拥有令牌的计算机得到权利传输自己的报文，而没有令牌的计算机则只允许转发报文。一般来说，每台计算机只是像传递报文那样传递令牌。然而，如果收到令牌的计算机有自己的报文需要通过网络传输，它就会保存令牌，同时传输一份报文。这份报文在环形网络中环绕一周后，该计算机就将令牌传递给环形网络中的下一台计算机。同样，当下一台计算机收到令牌时，它既可以立即传递令牌，也可以先传输自己的新报文，然后将令牌传递给下一台计算机。这样，随着令牌绕着环形网络传递，网络中的每台计算机都有同等的机会传输自己的报文。
Another protocol for coordinating message transmission is used in bus topology networks that are based on the Ethernet protocol collection. In an Ethernet system, the right to transmit messages is controlled by the protocol known as Carrier Sense Multiple Access with Collision Detection (CSMA／CD). This protocol dictates that each message be broadcast to all the machines on the bus .Each machine monitors all the messages but keeps only those addressed to itself．To transmit a message, a machine waits until the bus is silent，and at this time it begins transmitting while continuing to monitor the bus. If another machine also begins transmitting, both machines detect the clash and pause for a brief random period of time before trying to transmit again. The result is a system similar to that used by a small group of people in a conversation. If two people start to talk at once．they both stop. The difference is that people might go through a series such as，\"I'm sorry, what were you going to say?\first.\" whereas under the CSMA／CD protocol each machine merely tries again.
协调报文传输的另外一种协议用于基于以太网协议集的总线拓扑网络。在以太网系统中，传输报文的权利由称为带有冲突检测的载波侦听多路访问（CSMA/CD）的协议控制。该协议规定，每一份报文必须向总线上的所有计算机广播（图8A-2）。每台计算机监控所有的报文，但只保留发送给自己的那些报文。一台计算机要等到总线静默时才可以传输报文。这时，它开始传输报文，同时继续监控总线。 如果另一台计算机也开始传输报文，这两台计算机都会检测到冲突，并暂停短暂而随机的一段时间，然后再尝试传输。结果是形成一种，这种类似于一小群人对话时所采用的。如果两个人同时开始说话，他们都会停下来。不同的是，人们随后可能进行这样的对话：“抱歉，您想说什么？”，“不，不，您先说。”而根据CSMA/CD协议，每台计算机只是重新进行尝试
Interprocess Communication 进程间通信
The various activities (or processes) executing on the different computers within a network (or even executing on the same machine via time sharing) must often communicate with each other to coordinate their actions and to perform their designated tasks. Such communication between processes is called interprocess communication.
在一个网络内不同计算机上（甚至使用分时方法在同一台计算机上）执行的各种活动（或进程）必须经常互相通信，以便协调行动，并完成指定的任务。这种进程之间的通信称为进程间通信。
A popular convention used for interprocess communication is the client/server model. This model defines the basic roles played by the processes as either a client，which makes requests of other processes, or a server, which satisfies the requests made by clients.
进程间通信使用的一种流行规约是客户机/服务器模型。这种模型将进程扮演的基本角色或定义为向其他进程提出请求的客户机，或定义为满足客户机所提请求的服务器。
An early application of the client/server model appeared in networks connecting all the computers in a cluster of offices. In this situation a single, high-quality printer was attached to the network where it was available to all the machines in the network. In this case the printer played the role of a server (often called a print server), and the other machines were programmed to play the role of
clients that sent print requests to the print server.
客户机/服务器模型的一种早期应用，出现在将一组办公室里的所有计算机都连接起来的网络中。在这种应用中，一台高质量的打印机被连接到网络上，供其中的所有计算机使用。在这种情况下，打印机扮演了服务器（常称为打印服务器）的角色，而其他计算机则通过程序设计而扮演了向打印服务器发送打印请求的客户机角色。
Another early application of the client/server model was used to reduce the cost of disk storage while also removing the need for duplicate copies of records. Here one machine in a network was equipped with a high-capacity mass storage system (usually a magnetic disk) that contained all of an organization's records. Other machines on the network then requested access to the records as they needed them. Thus the machine that actually contained the records played the role of a server (called a file server)，and the other machines played the role of clients that requested access to the files that were stored at the file server
客户机/服务器模型的另外一种早期应用是为了降低磁盘存储费用，同时消除复制记录的
需要。在这种情况下，网络中的某一台计算机配备了大容量存储系统（通常是磁盘），存储一个机构的所有记录。这样，网络中的其他计算机可根据需要请求访问这些记录。因此，实际含有记录的计算机扮演了服务器（称为文件服务器）的角色，而其他计算机则扮演了请求访问文件服务器上存储的文件的客户机角色。
Today the client/server model is used extensively in network applications.
However, the client/server model is not the only means of interprocess communication. Another model is the peer-to-peer (often abbreviated P2P) model, whose properties provide insightful contrast to the client/server model. Whereas the client/server model involves one process (the server) communicating with numerous others (clients)，the peer-to-peer model involves two processes communicating as equals .Moreover, whereas a server must execute continuously so that it is prepared to serve its clients at any time，the peer-to-peer model usually involves two processes that execute on a temporary basis. For example, applications of the peer-to-peer model include instant messaging in which two people carry on a written conversation over the Internet as well as situations in which people play games such as chess or checkers.（ treating as equals） 平等待人
今天，客户机/服务器模型在网络中广泛应用。不过，客户机/服务器模型并非进程间通信的唯一方式。另外一种模型是对等（peer-to-peer，常缩写为P2P）模型，其特性与客户机/服务器模型的特性形成鲜明对照。客户机/服务器模型涉及一个进程（服务器）与许多其他进程（客户机）通信，而对等模型则涉及两个进程进行对等通信。而且，服务器必须持续运行，以准备好随时服务于客户机，而对等模型则通常涉及两个进程临时运行。例如，对等模型的应用包括两个人通过因特网进行书面对话的即时通信，以及人们参与下国际象棋或西洋跳棋等游戏的情况。 （continuously 连续不断的；continually 不断的（中间有小间断））
The peer-to-peer model is also a popular means of sharing files such as music recordings and motion pictures via the internet (sometimes with questionable legality). In this case individuals who are seeking particular items broadcast their
desire over the Internet and are contacted by those who own the items of interest. Then，the items are transferred between the two parties using the peer-to-peer model. This is in contrast to earlier approaches that applied the client/server model by establishing a central “distribution center” (the server) from which clients downloaded music recordings (or at least found sources for those items). The central server, however, proved to be a focal point at which the music industry could enforce copyright laws, leading to the eventual dismantling of these music distribution centers. In contrast, the lack of a centralized base of operation obtained via the peer-to-peer model makes legal efforts to enforce copyright laws more difficult.
对等模型还是通过因特网共享音乐录音、影片等文件的一种流行方法（其合法性有时值得怀疑）。在这种情况下，寻求特定项目的个人在因特网上发布其需求，而拥有他所感兴趣项目的人则会与他取得联系。然后，双方之间就可以使用对等模型传输这些项目。这与应用客户机/服务器模型的较早期方法截然不同，这些方法要建立一个“分发中心”（服务器），供客户机下载音乐录音（或者至少找到可以提供这些项目的地方）。然而，中心服务器证明是音乐行业可以运用版权法的一个焦点对象，结果最终导致这些音乐分发中心的解体。与此形成对照的是，对等模型缺乏一个操作中心，这使得运用版权法的努力难度增加。
You might often read or hear the term peer-to-peer network, which is an example of how misuse of terminology can evolve when technical terms are adopted by the nontechnical community. The term peer-to-peer refers to a system by which two processes communicate over a network (or internet). It is not a property of the network (or internet). A process might use the peer-to-peer model to communicate with another process and later use the client/server model
to communicate with another process over the same network. Thus, it would be more accurate to speak of communicating by means of the peer-to-peer model rather than communicating over a peer-to-peer network.
你或许经常读到或听到“对等网络”这个说法，这是当技术术语被非科技界采用时可能发生术语误用的一个例子。“对等”指的是两个进程通过网络（或互联网）进行通信的一种，并不是网络（或互联网）的一种特性。一个进程可以通过同一个网络先是使用对等模型与另一个进程通信，然后又使用客户机/服务器模型与另一个进程通信。因此，比较准确的说法是，使用对等模型通信，而不是通过对等网络通信。
第九单元
The most notable example of an internet is the Internet (note the uppercase I ), which originated from research projects going back to the early 1960s. The goal was to develop the ability to link a variety 0f computer networks so that they could function 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Ｉ）。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。
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 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 involving millions of computers.
最初的工作大多是由美国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。
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 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、公司或机构那样的组织负责运行。每个域是一个自主系统，可根据本地管理机构的愿望进行配置。
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组成.
域的建立由互联网名称与数字地址分配机构（ICANN）监管,
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。
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. This particular router is often referred to as the domain's gateway, in that it represents the domain's 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。
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 the internet outside the domain’s gateway is out of the domain’s control and is of minimal concern to the 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。 in reference to 根据； 关于
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。
If one \"stood\" at a domain's gateway and \"looked out\" into the cloud, one could find a variety of structures. Indeed, the Internet 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。
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.
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。in turn 轮流地，依次
II Connecting to the Internet
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 ISP's equipment or to become a part of a domain already established by the ISP.
II 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
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 Internet 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
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
These technologies have greatly reduced the expense of broadband (high-capacity) Internet access (which used to be available only to large organizations that could afford the expense of dedicated Internet connections), making today's 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。
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, making the home system a local network within a domain established by the ISP.
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，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.
The connection from the home‘s 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。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。
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。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。
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。
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.
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。
Each 32-bit address consists of two parts: 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.
每个32位地址由两部分构成：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。
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 domain's local authority--usually a person having a job title such as network administrator 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。
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）；
and the pattern 17.12.25 would represent the three-byte bit pattern consisting of the byte 0001000l (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).
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）。
Thus a computer in the domain of the Addison-Wesley publishing company might have the IP address 192.207.177.133, 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-Wesley's domain).
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
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）。
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 aw.com. Note that the naming system reflects the domain's classification, which in this case is commercial as indicated 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aw.com。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。
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、表示美国机构的gov、表示非赢利机构的org、表示博物馆的museum、表示无使用的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。
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.
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 aw. com might be
identified as ssenterprise.aw.com.
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（称为国家代码顶级域名），如表示澳大利亚的au和表示加拿大的ca。
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助记名，从而为域内的计算机取得助记名。例如， 位于aw.com 域内的一台计算机可能被标识为
ssenterprise.aw.com。
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 computer's location within a hierarchical classification system. In particular, the address ssenterprise.aw. com indicates that the computer known as ssenterprise is within the institution aw within the class (or TLD) of commercial domains com.
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。具体来说ssenterprise.aw.com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）
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. 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。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。
Then, a computer at Nowhere University could have an address such as r2d2.compsc.nowhereu.edu, meaning that the computer r2d2 is in the subdomain compsc within the domain nowhereu within the class of educational domains edu.
那么，乌有大学的一台计算机就可能具有像r2d2.compsc.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。
Each domain's 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。
Together, all the name servers throughout the Internet are part of an Internet-wide directory system known as the domain name system (DNS) that is used to convert addresses in mnemonic form into their equivalent bit-pattern forms. In particular, when a human requests that a message be sent to a destination identified in mnemonic form,
整个因特网的所有名称服务器一起构成一个因特网范围的目录系统的一部分，该系统
称为域名系统，用于将助记形式的地址转换成相应的位模式形式。具体来说，当一个人请求将一份报文发送到以助记形式标识的一个目的地时，
DNS is used to convert that mnemonic address into its equivalent IP address that is compatible with the Internet software. The process of extracting
information from DNS is often referred to as a \"DNS lookup.\" Normally, a DNS lookup is completed in a fraction of a second.
域名系统被用于将该助记地址转换成与因特网软件兼容的相应IP地址。从域名系统提取信息的过程常常被称为“域名系统查找”。一般来说，完成一个域名系统查找只需要几分之一秒。
第十单元
I. Introduction
E-mail is an electronic system for sending and receiving messages and files over a computer network. Compared to the phone or paper-based documents, e-mail is still relatively new in the workplace. When you are using e-mail, here are a few guidelines to keep in mind:
I. 引言
电子邮件是通过计算机网络收发消息及文件的一种电子系统。不过，与电话或纸质文档相比，电子邮件在工作场所中仍属于比较新的事物。这里有几条使用电子邮件时需记住
的指导原则：
E-mail is increasingly used for professional purposes --Not long ago, e-mall was considered a secondary form of communication. It was spontaneous and chatty, used mostly for quick comments or nonessential information. Today, e-mail is a principal form of communication in most workplaces, so people expect e-mail messages to be professional and nonfrivolous
电子邮件越来越多地用于专业目的——不久以前，电子邮件还被视为一种次要的交流形式。那时，它自然并具有聊天式的风格，大多用于表达未加深思的意见或传递
不重要的信息。今天，电子邮件在大多数工作场所已成为一种主要的交流形式。因此，人们期待,电子邮件具有专业性
E-mail is a form of public communication —— Your readers can purposely or mistakenly send your e-mail messages to countless others. So, you should not say things with e-mail that you would not say openly to your supervisors, coworkers, or clients
电子邮件是一种公开的交流形式——你的读者可能把你的电子邮件有意发给或误发给数不清的其他人。所以，你不应该用电子邮件说那些你不愿公开说给主管、同事
或客户听的事。
E-mail is increasingly formal -In the past, readers forgave typos, misspellings,
and bloopers in e-mail messages, especially when e-mail was new and difficult to use. Today. readers expect e-mails to be more formal, reflecting the quality expected in other forms of communication.
电子邮件越来越正式——过去，读者会原谅电子邮件中的打字错误、拼写错误以及失礼，特别是在电子邮件刚出现并难以使用的时候。今天，读者期待电子邮件更为正式，能够显示出对其他交流形式所期待的质量。
E-mail standards and conventions are still being formed——How e-mail should be used in the workplace is still being worked out. People hold widely different views about the appropriate (and inappropriate) use of e-mail. So, you need to pay close attention to how e-mail is used in your company and your reader’s companies. Many companies are developing policies explaining how e-mail should be used. If your company has a policy on e-mail usage, you should read it and follow it.
电子邮件标准和常规还在形成中——电子邮件在工作场所应该如何使用，这一点还在探索中。关于电子邮件的适当（以及不适当）使用，人们持有相差甚远的看法。因此，你需要密切关注在你的公司和你读者的公司中电子邮件是如何使用的.许多公司正在制订阐述如何使用电子邮件的.如果你的公司制定有关于电子邮件使用的，你应该阅读并遵循该。
You should also keep in mind that legal constraints shape how e-mail is used in the workplace. E-mail, like any other written document, is protected by copyright law. So, you need to be careful not to use e-mails in any way that might
violate copyright law. For example, if you receive an e-mail from a client, you cannot immediately post it to your company's website without that client's permission.
你还应该记住，法律约束对在工作场所如何使用电子邮件具有决定性作用。像任何其他的书面文档一样，电子邮件受版权法保护。因此，你得小心，不要以可能触犯版权法的任何方式使用电子邮件。例如，如果你收到一位客户的电子邮件，在没有得到该客户允许的情况下，你不能将电子邮件马上发布到你公司的网站上。
Also, lawyers and courts treat e-mail as written communication, equivalent to a memo or letter. For example, much of the antitrust case against Microsoft in the late 1990s was built on recovered e-mail messages in which Bill Gates and other executives chatted informally about aggressively competing with other companies.
还有，律师和法庭把电子邮件视为书面通信，将其等同于备忘录或信函。例如，20世纪90年代末针对微软的反垄断案在很大程度上就是以恢复的电子邮件为根据的；在这些电子邮件中，比尔·盖茨和其他经营主管人员非正式地聊到与其他公司展开大胆有力的竞争。
Legally, any e-mail you send via the employer's computer network belongs to the employer. So, your employers are within their rights to read your e-mail without your knowledge or permission. Also, deleted e-mails can be retrieved from the company's servers, and they can be used in a legal case.
从法律上讲，你通过雇主的计算机网络发送的任何电子邮件都属于雇主。因此，你的雇主有权阅读你的电子邮件而无需你知道或得到你的允许。另外，删除的电子邮件可从公司的服务器上恢复，而且它们可用于法律案件
Increasingly, harassment and discrimination cases hinge on evidence found in e-mails. Careless e-mails about personal relationships or appearances can be saved and used against the sender in a court case. Indiscreet comments about gender, race, or sexual orientation can also have unexpected consequences. Your \"harmless\" dirty jokes sent to your coworkers might end up being used by a lawyer to prove that you are creating a \"hostile workplace environment.\"
骚扰和歧视案件越来越多地取决于在电子邮件中找到的证据。关于个人关系或容貌的轻率电子邮件可能被保存并在法庭案件审理中用于对付发送人。关于性别、种族或性取向缺乏慎重的议论也可能带来意想不到的后果。你发送给同事的“无恶意的”黄色笑话，最终可能被律师用于证明你在制造一个“不利的工作环境”
II. Basic Features of E-Mall
An e-mail is formatted similarly to a memo. Typical e-mail messages will have a header and body. They also have additional features like attachments and signatures.
Header
The header has lines for To and Subject. Usually, there are also lines like cc, bcc,
and Attachments, which allow you to expand the capabilities of the message.
电子邮件的基本特征
电子邮件的格式编排类似于备忘录。典型的电子邮件有题头和正文。它们还有附件、签名等附加特征。
1．题头
题头有用于填写收件人和主题的行。通常，还会有允许你扩展邮件功能的其他行，如抄送、密送、附件等。
To line——Here is where you type the e-mail address of the person to whom you are sending the e-mail. You can put multiple addresses on this line, allowing you to send your message to many people
收件人行——这是你键入你向其发送电子邮件的人的电子邮件地址的地方。你可以在该行输入多个地址，允许你向多人发送邮件。
cc and bcc lines ---They are used to copy the message to people who are not the primary readers, like your supervisors or others who might be interested in your conversation. The cc line shows your message's recipient that others are receiving copies of the message too. The bcc line (\"blind cc\") allows you to copy your messages to others without anyone else knowing.
抄送和密送行——这些行用于复制邮件给次要读者，如你的主管或者对你的交谈可能
感兴趣的其他人。抄送行向收件人表明，有其他人在接收邮件的副本。密送行允许你在别人不知晓的情况下将邮件复制给他人。
Subject line ---It signals the topic of the e-mail. Usually a small phrase is used. If the message is a response to a prior message, e-mail programs usually automatically insert a \"Re:'' into the subject line. If the message is being forwarded, a \"Fwd:'' is inserted in the subject line.
主题行——该行标明电子邮件的话题，通常使用简短的语句。如果该邮件是对以前邮件的回复，则电子邮件程序通常会在主题行自动插入“回复：”。如果转发邮件，则在主题行插入“转发：”.
Attachments line --It signals whether there are any additional files, pictures, or programs attached to the e-mail message. You can attach whole documents created on your word processor, spreadsheet program, or presentation software. An attached document retains its original formatting and can be downloaded right to the reader's computer.
附件行——该行标明是否有任何其他文件、图片或程序附加于电子邮件之中。你可以附加在你的文字处理软件、电子数据表程序或演示软件中创建的整个文档。附加的文档会保持其原有格式，并可直接下载到读者的计算机中。
. Message Area
After the header, the message area is where you can type your comments to
your readers. It should have a clear introduction, body, and conclusion.
● The introduction should minimally (1) define the subject, (2) state your purpose, and (3) state your main point. Also, if you want the reader to do something, you should mention it up front, not at the end of the e-mail.
信息区
信息区在题头下面，是你可键入致读者的话语的地方。它应该有清楚明白的引言、正文和结尾。
● 引言应尽可能简短地（1）表明主题、（2）说明用意并（3）阐述要点。还有，如果你想让读者做某事，你应该在最前面提出，而不是在电子邮件的结尾。
The body should provide the information needed to prove or support your e-mail's purpose.
The conclusion should restate the main point and look to the future, Most readers of e-mall never reach the conclusion, so you should tell them any action items early in the message and then restate them in the conclusion.
正文应提供证明或支持你的电子邮件用意所需的信息。
结尾应重申要点并展望未来。大多数电子邮件读者从来不看到结尾，因此你应该在邮件中提早告诉他们任何行动项目，然后在结尾部分予以重申。
The message area might also include these other kinds of text:
Reply text--When you reply to a message, most e-mail programs allow you to copy parts of the original message into your message, These parts are often identified with > arrows running down the left margin.
信息区可能还包括其他类型的文本：
● 回复文本——当你回复一封邮件时，大多数电子邮件程序允许你将原邮件的有关部分复制到你的邮件中。这些部分常常用沿着左面的页边空白向下排列的箭头>标出
Links—You can also add in direct links to websites. Most programs will automatically
recognize
a
webpage
address
like
\"http://www.predatorconservation.org\" and make it a live link in the e-mail's message area.
链接— 你还可以添加与网站的直接链接。大多数程序将自动识别一个像 http://www.predatorconservation.org 的网页地址，并使其成为电子邮件信息区的一个活链接。
。● Attachments——If you attach a file to your e-mail message, you should tell the readers in the message area that a file is attached. Otherwise. they may not notice it.
● 附件——如果你给你的电子邮件附加了一个文件，你应该在信息区告诉读者邮件中
附加了一个文件。不然的话，他们也许注意不到该附件。
● Emoticons——Another common feature in the message area is the use of emoticons. Used sparingly, they can help you signal emotions that are hard to convey in written text. When overused, emoticons can become annoying to some readers. In most workplace situations, emoticons should not be used.
● 情感符——信息区的另外一个常见特征是情感符的使用。如果有节制地使用,情感符可有助于你表明用书写的文本难以传达的情感。但是，如果使用过度,情感符可能使有些读者感到烦恼。在大多数工作场所的情景下，不应使用情感符。
They are playful and informal; therefore,they are really only appropriate in e-mails between close colleagues or friends.
Symbols Meaning
:-) Happy face
;-) Winking happy face
:-o Surprised face
它们具有嬉戏和非正式的性质，因此，确实只适用于关系密切的同事或朋友之间的电子邮件。
符号 意思
:-) 愉快的表情
;-) 使眼色的愉快表情
:-o 吃惊的表情
:-| Grim face
:-\\ Smirking face
:-( Unhappy face
;-( Winking unhappy face
:-x Silent face
:'-( Crying
:-| 板着面孔的表情
:-\\ 假笑的表情
:-( 不愉快的表情
;-( 使眼色的不愉快表情
:-x 沉默的表情
:'-( 哭泣
3. Signature
E-mail programs usually let you create a signature file that automatically puts a signature at the end of your messages. Signature files can be both simple and complex. They allow you to personalize your message and add in additional contact information. By creating a signature file, you can avoid typing your name, title, phone number, etc. at the end of each message you write.
3．签名
电子邮件程序通常允许你创建一个签名文件，该文件可在邮件结尾自动加上签名。签名文件可繁可简。它们允许你个性化你的邮件，并添加额外联系信息。通过创建签名文件，你可以避免在你写的每封邮件的结尾处打上姓名、头衔、电话号码，等等。
4. Attachments
One of the advantages of e-mail over other forms of communication is the ability to send and receive attachments. Attachments are files, pictures, or programs that readers can download to their own computer.
4．附件
与其他的交流形式相比，电子邮件的一个优势是能够收发附件。附件是读者可以下载到自己计算机上的文件、图片或程序。
● Sending attachments——lf you would like to add an attachment to your e-mail message, click on the button that says \"Attach Document\" or \"Attachment\" in your e-mail software program. Most programs will then open a textbox that allows you to find and select the file you want to attach.
● 发送附件——你如果想为电子邮件添加附件，那就点击你的电子邮件软件程序中的“添加文档”或“附件”按钮。大多数程序随即会打开一个文本框，允许你查找并选择想要附加的文件。
● Receiving attachments---If someone sends you an attachment, your e-mail program will use an icon to signal that a file is attached to the e-mail message. Click on that icon. Most e-mail programs will then allow you to save the document to your hard disk. From there, you can open the file.
● 接收附件——如果某人发给你一个附件，你的电子邮件程序会使用一个图标，来表示有文件附加于电子邮件。点击该图标，大多数电子邮件程序随即会让你将该文档保存到硬盘上。你可以再从那里打开该文件。
III. E-Mail Netiquette
E-mail has its own etiquette or \"netiquette.\" Here are a dozen netiquette guidelines that you can follow in the workplace:
● Be concise——Keep the length of your messages under a screen and a half. If you have more than a screen and a half of content, pick up the phone, write a memo, or send the information as an attachment.
III. 电子邮件应遵守的网规
电子邮件有自己的规矩或“网规”。这里有你在工作场所可以遵循的12条网规：
● 简洁——将邮件长度保持在一屏半以内。如果内容超过一屏半，应打电话、写备忘录或者将有关信息作为附件发送。
Provide only need-to-know information ---Decide who needs to know what you have to say, and send them only information they need--nothing more.
Treat the security of the message about the same as a message on a postcard---Recognize that anyone can pass your message along or use it against you. If the message is confidential or proprietary, e-mail is not an appropriate way to send it.
● 仅提供需要知道的信息——决定谁需要知道你要说的内容，然后仅给他们发送他们需要的信息——仅此而已。
● 视电子邮件中信息的安全度几近于明信片上信息的安全度——要认识到任何人都可能转发你的邮件或者用它来对付你。如果信息是秘密的或专属的，电子邮件不是一种适当的传送方式。
Don't say anything over e-mail that you would not say in a meeting or to legal authorities---Hey, accidents happen. You might send something embarrassing to the entire organization. 0r,someone might do it for you.
● 不要通过电子邮件说任何你不愿在会议上或对司法当局说的话——嘿，意外事件可能发生。你可能将令人难堪的东西发送给整个机构。或者，某个人可能替你这样做。
Never immediately respond to a message that made you angry or upset --Give yourself time to cool off. You should never write e-mail when you are angry, because these little critters have a way of returning to bite you.
● 千万不要立即回复令你愤怒或不安的邮件——给你自己时间冷静下来。你愤怒的时候，千万别写电子邮件，因为这些小畜生有办法反咬你一口。
Avoid using too much humor, especially irony or sarcasm--in an e-mail, your witty quips rarely come off exactly as you intended. Remember that your e-mails can be easily misinterpreted or taken out of context. The American sense of humor, meanwhile, is often disturbing to international audiences; so if your message is going overseas, keep the humor to a minimum.
避免使用过多的幽默，特别是反语或讽刺——在电子邮件中，你的诙谐俏皮话难得达到你想要的确切效果。记住你的电子邮件可能很容易被误解或断章取义。同时,美国人的幽默感经常让外国读者感到烦恼。因此，如果你的邮件是发往海外的，应尽可能少地使用幽默。
Be extra careful about excerpting or forwarding the e-mail of others--lf there is the remotest chance that someone else’s message could be misunderstood, paraphrase it in your own message instead of forwarding it or copying parts of it.
摘引或转发他人的电子邮件要格外慎重——如果其他人的邮件有丝毫的被误解的可能性，则应在你自己的邮件中解释转述，而不应将其转发或部分复制。
Don't be unpleasant over e-mail if you would not be so face to face--E-mail provides a false sense of security, much like driving in a car. But in reality, those are real people on that information superhighway, and they have feelings. Plus they can save your abusive or harassing messages and use them as evidence against you.
如果你与人面对面时不愿令人不快的话，那在电子邮件中也不要——与在车中驾驶很相像，电子邮件给人以虚假的安全感。但是，实际上，信息高速公路上的那些人都是真人，他们是有感情的。另外，他们可以保存你的谩骂性或骚扰性邮件，并将其用作对付你的证据。
Never send anything that could be proprietary --There have been some classic cases where classified information or trade secrets have been sent to competitors or the media over e-mail. If the information is proprietary, use traditional routes like the regular mail or a courier.
千万不要发送任何可能具有专属性质的东西——有一些经典案例，在这些案例中保密信息或行业秘密通过电子邮件发送给了竞争者或媒体。如果信息是专属的，应使用传统传
递途径，如普通邮件或信使。
Don't flame, spam, or chain-letter people at work--if you must, do these things from your personal computer at home. At work, assume these activities will ultimately be used against you. You might be fired.
不要在工作场所向人发送争论邮件、垃圾邮件或连锁邮件——如果你必须做这些事，则应在家里用你的个人电脑。在工作场所，应假定这些活动最终会被用于对付你.你可能被解雇。
Think twice before you send \"urgent\" messages that are making their way across the net--There are lots of hoaxes about computer viruses \"erasing your hard drive.\" These hoaxes gain new life when some gullible persons start sending them to all their friends. Some viruses are real, but most are not. Wait a day or two to see if the threat is real before you warn all your friends and colleagues.
发送网上流行的“紧急”消息应三思而后行——有很多关于计算机病毒“擦除你硬盘上数据”的恶作剧。当某些易上当的人开始向其所有朋友发送这些恶作剧消息时,它们便获得了新的活力。有些病毒是真的，但大多数不是。在你向所有朋友和同事发出警告之前，应先等一两天，看看威胁是真是假。
Be forgiving of the grammatical mistakes of others--but don't make them yourself--some people treat e-mail informally, so they rarely revise (though they should). Grammar mistakes and misspellings happen--so you can forgive the sender. On the other hand, these mistakes and typos make the sender look stupid,
Don't send out sloppy e-mail messages.
原谅别人的语法错误，但你自己不要犯——有些人视电子邮件为非正式交流方式，因此他们很少进行修改（尽管他们应该这样做）。语法错误和拼写错误不免发生，所以你可要原谅发件人。另一方面，这些错误使发件人显得愚蠢，因此，不要发出马虎的电子邮件。
第十一单元
Electronic Commerce(电子商务)
Section A
Electronic Commerce
I．Introduction
The business phenomenon that we now call electronic commerce has had an interesting history.
我们现在称之为电子商务的商业现象拥有有趣的历史。
From humble beginnings in the mid-1990s, electronic commerce grew rapidly until 2000, when a major downturn occurred.
电子商务发端于20世纪90年代中期，当时并不显山露水，但随后发展迅猛，直到2000年出现一次大衰退。
Many people have seen news stories about the “dot-com boom” followed by the “dot-com bust” or the “dot-bomb.” Beginning in 2003, electronic commerce began to show signs of new life.
许多人看过相关的新闻报道，先是“网络公司繁荣”，继之以“网络公司不景气”或“网络”。从2003年开始，电子商务开始显示出新生的迹象。
Although the rapid expansion and high levels of investment of the boom years are not likely to be repeated, the second wave of electronic commerce is well underway.
尽管繁荣岁月的快速扩张和高水平投资不可能重现，但电子商务的第二次浪潮已然来临。
To many people, the term “electronic commerce” means shopping on the part of the Internet called the Word Wide Web (the Web).
对于许多人来说，“electronic commerce”（电子商务）这个术语表示在称为万维网的那一部分因特网上购物。
However, electronic commerce (or e-commerce) also includes many other activities, such as businesses trading with other businesses and internal processes that companies use to support their buying, selling, hiring, planning, and other activities.
然而，electronic commerce（或e-commerce）也包括许多其他的活动，如一个企业与其他企业的贸易，以及公司用于支持其购买、销售、招聘、计划及其他活动的内部过程。
Some people use the term “electronic business” (or e-business) when they are talking about electronic commerce in this broader sense. Most people use the terms “electronic commerce” and “electronic business” interchangeably.
有些人从这种比较广泛的意义上谈论电子商务时，使用“electronicbusiness”（或e-business）这个术语。大多数人混用“electronic commerce”和“electronicbusiness”这两个术语。
Here the term “electronic commerce” is used in its broadest sense and includes all business activities conducted using electronic data transmission technologies.
“electronic commerce”这个术语在本文中是从最广泛的意义上使用的，包括使用电子数据传输技术进行的所有商业活动。
The most common technologies used are the Internet and the Word Wide Web, but other technologies, such as wireless transmissions on mobile telephone and personal digital assistant (PDA) devices, are also included.
最常用的技术是因特网和万维网，但所使用的技术也包括其他技术，如通过移动电话和个人数字助理设备进行的无线传输。
Some people find it useful to categorize electronic commerce by the types of entities participating in the transactions or business processes.
有些人感到根据参与交易或商业过程的实体类型对电子商务进行分类比较有用。
The five general electronic commerce categories are business-to-consumer, business-to-business,
business
processes,
consumer-to-consumer,
and
business-to-government.
有5种一般的电子商务类型，分别是：企业对消费者电子商务、企业对企业电子商务、商业过程、消费者对消费者电子商务和企业对电子商务。
The three categories that are most commonly used are:
·Consumer shopping on the Web, often called business-to-consumer (or B2C)
最常用的3种类型是：
● 消费者在网上购物，常称为企业对消费者（或B2C）电子商务
· Transactions conducted between businesses on the Web, often called business-to-business (or B2B)
● 企业之间在网上进行的交易，常称为企业对企业（或B2B）电子商务
· Transactions and business processes that companies, governments, and other organizations undertake on the Internet to support selling and purchasing activities.
● 公司、及其他机构为支持买卖活动而在因特网上采取的交易与商业过程
Figure 11A-1 shows the three main elements of electronic commerce. The figure presents a rough approximation of the relative size of these elements.
该图显示了对这些要素相对规模的粗略估计。
In terms of dollar volume and number of transactions, B2B electronic commerce is much greater than B2C electronic commerce.
就美元值和交易数量而言，B2B电子商务比B2C电子商务大得多。
However, the number of supporting business processes is greater than the number of all B2C and B2B transactions combined.
然而，支持商业过程的数量比所有B2C和B2B交易加在一起的数量还要多。
The large oval in Figure 11A-1 that represents the business processes that support selling and purchasing activities is the largest element of electronic commerce.
图11A-1中表示支持买卖活动的商业过程的大椭圆形代表电子商务的最大要素。
Some researchers define a fourth category of electronic commerce, called consumer-to-consumer (or C2C), which includes individuals who buy and sell items among themselves.
有些研究人员还界定了另外一种电子商务，称为消费者对消费者（或C2C）电子商务。这种电子商务指个人之间买卖物品。
For example，C2C electronic commerce occurs when a person sells an item through a Web auction site to another person.
例如，一个人通过拍卖网站向另一个人出售一件物品便是C2C电子商务。
Finally, some researchers also define a category of electronic commerce called business-to-government (or B2G);
最后，有些研究人员还界定了一种称为企业对（或B2G）的电子商务。
this category includes business transactions with government agencies, such as paying taxes and filing required reports.
这种类型的电子商务包括企业与机构的交易，如交税和填写规定的报表。
An increasing number of states have Web sites that help companies do business with state government agencies.
数量越来越多的州建有帮助公司与州机构做生意的网站。
For example, the CAL-Buy site makes it easy for businesses to conduct online transactions with the State of California. Figure 11A-2 summarizes these five categories of electronic commerce.
例如，CAL-Buy网站使企业与加利福尼亚州进行在线交易变得容易。图11A-2概括了以上5种电子商务。
Economists Chris Freeman and Francisco louca describe four waves that occurred in the Industrial Revolution in their book As Time Goes By.
经济学家克里斯·弗里曼和弗朗西斯科·卢桑在他们的《随着时间流逝》一书中描述了
工业发生的4次浪潮。
Many researchers predict that electronic commerce and the information revolution brought about by the Internet will go through similar waves. Those researchers agree that the second wave of electronic commerce has begun.
许多研究人员预言，因特网带来的电子商务和信息将经历类似的浪潮。这些研究人员一致认为，电子商务的第二次浪潮已经开始。
The first wave of electronic commerce was primary a U.S. phenomenon. Web pages were primarily in English, particularly on commerce sites.
电子商务的第一次浪潮主要是一种美国现象。网页主要用英语编写，特别是商业网站的网页。
As the second wave begins, it is clear that the future of electronic commerce will be international in scope and will allow sellers to do business in many countries and in many languages.
随着第二次浪潮的开始，很明显，未来的电子商务将是国际范围的，并将允许卖方在许多国家和用多种语言做生意。
The problems of language translation and handling currency conversion will need to be solved to allow efficient conduct of business in the second wave.
为了在第二次浪潮中能够高效地做生意，将需要解决语言翻译和货币兑换问题。
In the first wave, easy access to start-up capital led to an overemphasis on creating new large enterprises to exploit electronic commerce opportunities.
在第一次浪潮中，创办资金比较容易得到，这导致人们过分强调创办新的大型企业，以利用电子商务机会。
Investors were excited about electronic commerce and wanted to participate, no matter how much it cost or how bad the underlying ideas were.
投资者对电子商务感到兴奋，而且，无论花费多么大或基本想法多么糟糕，他们都想参与电子商务。
In the second wave, established companies are using their own internal funds to finance gradual expansion of electronic commerce opportunities.
在第二次浪潮中，已站住脚的公司使用自己的内部资金来为逐步扩大电子商务机会提供经费。
These measured and carefully considered investments are helping electronic commerce grow more steadily, although more slowly.
这些经过仔细考虑的慎重投资在帮助电子商务更加稳步地发展，虽然发展的速度比以前缓慢。
The Internet technologies used in the first wave, especially in B2C commerce, were slow and inexpensive. Most consumers connected to the Internet using dial-up modems.
在第一次浪潮中，尤其是在B2C商务中，所使用的因特网技术速度慢，费用低廉。大多数消费者使用拨号调制解调器连接到因特网上。
The increase in broadband connections in homes is a key element in the second wave. Although these connections are more expensive, they are more than 10 times faster.
家里宽带连接的增加是第二次浪潮的一个关键要素。这些连接尽管费用比较高，但速度快了10倍多。
This increased speed not only makes Internet use more efficient, it can alter the way people use the Web.
这种速度提高不仅提高了使用因特网的效率，而且可以改变人们使用万维网的方式。
In the first wave, Internet technologies were integrated into B2B transactions and internal business processes by using bar codes and scanners to track parts, assemblies, inventories, and production status.
在第一次浪潮中，因特网技术通过使用条形码和扫描仪跟踪零部件、库存和生产状况而结合进B2B交易和内部商业过程。
In the second wave, radio-frequency identification (RFID) devices and smart cards are being combined with biometric technologies such as fingerprint readers and retina scanners to control more items and people in a wider variety of situations.
在第二次浪潮中，射频识别装置和智能卡正在与指纹读取器、视网膜扫描仪等生物统计学技术结合起来，以便在更为广泛多样的情况下控制更多的物品和人员。
These technologies are increasingly integrated with each other and with communication systems that allow companies to communicate with each other and share transaction, inventory level, and customer demand information effectively.
这些技术正在越来越高的程度上互相整合，并与有关的通信系统整合，这些通信系统使不同的公司能够互相通信，有效地分享交易、库存量及顾客需求信息。
The use of electronic mail (or e-mail) in the first wave was as a tool for relatively unstructured communication. In the second wave, sellers are using e-mail as an integral part of their marketing and customer contact strategies.
在第一次浪潮中，电子邮件是作为一种进行较为松散的通信的工具使用的。在第二次浪潮中，卖方是将电子邮件作为其营销与顾客联系策略的不可缺少的组成部分来使用的。
Online advertising was the main revenue source of many failed dot-com businesses in the first wave.
在第一次浪潮中，在线广告是许多后来倒闭了的网络公司的主要收入来源。
After a two-year dip in online advertising activity and revenues, companies are beginning the second wave with a renewed interest in making the Internet work as an effective advertising medium.
经过两年的在线广告活动与收入下降之后，随着第二次浪潮的开始，一些公司又对使因特网成为一种有效的广告媒介发生兴趣。
Some categories of online advertising, such as employment services are growing rapidly and are replacing traditional advertising outlets.
有些在线广告类型，如招聘服务，在迅速发展，并在取代传统的广告发布渠道。
The sale of digital products was fraught with difficulties during the first wave of electronic commerce. The music recording industry was unable (or, some would
ay, unwilling) to devise a way to distribute digital music on the Web.
在电子商务的第一次浪潮中，数字产品的销售充满困难。音乐录制行业无法（或者，有些人会说，不愿）想出一种方法在网上分发数字音乐。
This created an environment in which digital piracy-the theft of musical artists’ intellectual property—become rampant. The promise of electronic books was also unfulfilled.
这导致了一种环境的形成，在这种环境下数字盗版——盗窃音乐艺术家的知识产权——变得十分猖獗。此外，电子图书也未实现其预期的前景。
The second wave offers the promise of legal distribution of music, video, and other digital products on the Web.
第二次浪潮提供了在网上合法分发音乐、视频及其他数字产品的可能性。
Apple Computer’s iTunes site is one of the early second wave attempts at digital product distribution.
苹果计算机公司的iTunes站点是第二次浪潮在数字产品分发方面的早期尝试之一。
Figer11A-3 shows a summary of some key characteristics of the first wave and the second wave of electronic commerce.
图11A-3概括了电子商务第一次浪潮和第二次浪潮的一些关键特点。
This list is not complete because every day brings new technologies and combinations of existing technologies that make additional second wave opportunities possible.
该列表并不全面，因为每天都带来新的技术和现有技术的新结合，它们使新的第二次浪潮机会的产生成为可能。
Not all of the future of electronic commerce is based in its second wave. Some of the first wave companies were successful, such as Amazon.com, eBay, and Yahoo! .
电子商务的未来并非完全基于第二次浪潮。第一次浪潮中诞生的公司有些取得了成功，如Amazon.com、eBay和雅虎。
The second wave of electronic commerce will provide new opportunities for these businesses, too.
电子商务的第二次浪潮也将为这些企业提供新的机会。
第十二单元
(1) Employees
The largest category of computer criminals consists of those with the easiest access to computers—namely, employees. Sometimes the employee is simply trying to steal something from the employer—equipment, software, electronic
funds, proprietary information, or computer time. Sometimes the employee may be acting out of resentment and is trying to “get back” at the company.
人数最多的计算机罪犯类型由那些最容易接近计算机的人，亦即雇员，构成。有时，雇员只是设法从雇主那盗窃某种东西——设备、软件、电子资金、专有信息或计算机时间。有时，雇员可能出于怨恨而行动，试图“报复”公司。
(2) Outside Users
Not only employees but also some suppliers or clients may have access to a company’s computer system. Examples are bank customers who use an automatic teller machine. Like employees, these authorized users may obtain confidential passwords or find other ways of committing computer crimes.
不仅雇员，而且有些供应商或客户也可能有机会访问公司的计算机系统。使用自动柜员机的银行客户就是一例。像雇员一样，这些授权的用户可能获取秘密口令，或者找到进行计算机犯罪的其他途径。
(3) “Hackers” and “Crackers”
Some people think of these two groups as being the same, but they are not. Hackers are people who gain unauthorized access to a computer system for the fun and challenge of it. Crackers do the same thing but for malicious purposes. They may intend to steal technical information or to introduce what they call a “bomb”—a destructive computer program—into the system.
有些人以为这两类人相同，其实不然。黑客获取对计算机系统未经授权的访问，是因为这种行为有趣和具有挑战性。非法侵入者行为相同，但出于恶意。他们可能企图窃取技术信息，或者往系统里放置他们所谓的“”——一种破坏性计算机程序。
(4) Organized Crime
Organized crime has discovered that computers can be used just like legitimate business people use them, but for illegal purposes. For example, computers are useful for keeping track of stolen goods or illegal gambling debts. In addition, counterfeiters and forgers use microcomputers and printers to produce sophisticated-looking documents such as checks and driver’s licenses.
犯罪团伙发现，可以像合法的商业人员一样使用计算机，但为了非法的目的。例如，计算机可用于跟踪赃物或非法赌债。另外，伪造者使用微机和打印机伪造支票、驾驶证等看起来很复杂的证件。
(1) Damage
Disgruntled employees sometimes attempt to destroy computers, programs, or files. In recent years, computer viruses have gained wide notoriety. Viruses are programs that “migrate” through networks and operating systems and attach themselves to different programs and databases.
不满的雇员有时企图破坏计算机、程序或文件。近年来，计算机病毒已是臭名远扬。病毒是一种程序，在网络和操作程序中“迁移”，并附加到不同的程序和数据库上。
病毒的一个变种是蠕虫病毒。这种破坏性程序用自我复制的信息填满计算机系统，以阻塞系统，使系统的运行减慢或停止。
A variant on the virus is the worm. This destructive program fills a computer system with self-replicating information, clogging the system so that its operations are slowed or stopped. The most infamous is known as the Internet Worm. In 1988, it traveled across North America, stopping thousands of computers along its way.
病毒的一个变种是蠕虫病毒。这种破坏性程序用自我复制的信息填满计算机系统，以阻塞系统，使系统的运行减慢或停止。其中最臭名昭著的是因特网蠕虫。1988年，它行遍北美，途中使成千上万的计算机瘫痪。
Viruses typically find their way into microcomputers through copied floppy disks or programs downloaded from electronic bulletin boards. Because viruses can be so serious—certain “disk-killer” viruses can destroy all the information on one’s system—computer users are advised to exercise care in accepting new programs and data from other sources.
病毒一般是通过复制的软盘或从电子公告版上下载的程序进入微机。因为病毒可造成严重危害——某些“磁盘杀手”病毒能毁坏系统上的所有信息，建议计算机用户在接受来自其他途径的新程序和数据时一定要小心。
Detection programs called virus checkers are available to alert users when certain kinds of viruses enter the system. Unfortunately, new viruses are being developed all the time, and not all viruses can be detected. There are
recommended procedures to reduce the risk of catching a computer virus and to minimize its potential damage.
现在有被称为病毒检查程序的检测程序可供使用，在某些种类的病毒进入系统时，向用户发出警告。不幸的是，新的病毒不断被开发出来，而且并不是所有的病毒都能被检测出来。现在有降低计算机病毒感染风险并尽量减少其潜在破坏的推荐步骤。
(2) Theft
Theft can take many forms—of hardware, of software, of data, of computer time. Thieves steal equipment, of course, but there are also “white-collar crimes.” Thieves steal data in the form of confidential information such as preferred client lists. They also use (steal) their company’s computer time to run another business.
（2）盗窃
盗窃可能采取多种形式——盗窃硬件、盗窃软件、盗窃数据、盗窃计算机时间等。窃贼当然盗取设备，但也有“白领犯罪行为”。窃贼盗取被看作机密信息的数据，如优先客户名单。他们也使用（盗窃）公司的计算机时间处理其他事务。
Unauthorized copying—a form of theft—of programs for personal gain is called software piracy. Pirated software accounts for 40 percent of software used in the United States. The incidence of pirated software is even higher overseas in such countries as Italy (82 percent) and Thailand (92 percent).
为个人利益而对程序进行的未经授权的拷贝也是一种盗窃形式，被称为软件盗版。盗版软件占到美国所使用的软件的40%。盗版软件在海外的比例甚至更高，如在意大利（82%）和泰国（92%）等国家。
(3) Manipulation
Finding entry into someone’s computer network and leaving a prankster’s message may seem like fun, which is why hackers do it. It is still against the law. Moreover, even if the manipulation seems harmless, it may cause a great deal of anxiety and wasted time among network users.
（3）操作
进入某人的计算机网络并留下恶作剧式的信息，可能显得很好玩。这也是为什么黑客这样做的原因。这样做仍然是违法的。此外，即使这样的操作似乎没有危害，它也可能给网络用户造成很大的焦虑和时间浪费。
The most notable example of an internet is the Internet (note the uppercase I ), which originated from research projects going back to the early 1960s. The goal was to develop the ability to link a variety 0f computer networks so that they could function 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Ｉ）。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。
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 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 involving millions of computers.
最初的工作大多是由美国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。
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 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、公司或机构那样的组织负责运行。每个域是一个自主系统，可根据本地管理机构的愿望进行配置。
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组成.
域的建立由互联网名称与数字地址分配机构（ICANN）监管,
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。
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. This particular router is often referred to as the domain's gateway, in that it represents the domain's 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。
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 the internet outside the domain’s gateway is out of the domain’s control and is of minimal concern to the 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。 in reference to 根据； 关于
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。
If one \"stood\" at a domain's gateway and \"looked out\" into the cloud, one could find a variety of structures. Indeed, the Internet 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。
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.
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。in turn 轮流地，依次
II Connecting to the Internet
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 ISP's equipment or to become a part of a domain already established by the ISP.
II 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
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 Internet 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
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
These technologies have greatly reduced the expense of broadband (high-capacity) Internet access (which used to be available only to large organizations that could afford the expense of dedicated Internet connections), making today's 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。
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, making the home system a local network within a domain established by the ISP.
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，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.
The connection from the home‘s 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。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。
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。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。
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。
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.
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。
Each 32-bit address consists of two parts: 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.
每个32位地址由两部分构成：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。
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 domain's local authority--usually a person having a job title such as network administrator 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。
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）；
and the pattern 17.12.25 would represent the three-byte bit pattern consisting of the byte 0001000l (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).
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）。
Thus a computer in the domain of the Addison-Wesley publishing company might have the IP address 192.207.177.133, 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-Wesley's domain).
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
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）。
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 aw.com. Note that the naming system reflects the domain's classification, which in this case is commercial as indicated 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aw.com。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。
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、表示美国机构的gov、表示非赢利机构的org、表示博物馆的museum、表示无使用的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。
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.
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 aw. com might be
identified as ssenterprise.aw.com.
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（称为国家代码顶级域名），如表示澳大利亚的au和表示加拿大的ca。
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助记名，从而为域
内的计算机取得助记名。例如， 位于aw.com 域内的一台计算机可能被标识为ssenterprise.aw.com。
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 computer's location within a hierarchical classification system. In particular, the address ssenterprise.aw. com indicates that the computer known as ssenterprise is within the institution aw within the class (or TLD) of commercial domains com.
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。具体来说ssenterprise.aw.com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）
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. 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。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。
Then, a computer at Nowhere University could have an address such as r2d2.compsc.nowhereu.edu, meaning that the computer r2d2 is in the subdomain compsc within the domain nowhereu within the class of educational domains edu.
那么，乌有大学的一台计算机就可能具有像r2d2.compsc.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。
Each domain's 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。
Together, all the name servers throughout the Internet are part of an Internet-wide directory system known as the domain name system (DNS) that is used to convert addresses in mnemonic form into their equivalent bit-pattern forms. In particular, when a human requests that a message be sent to a destination identified in mnemonic form,
整个因特网的所有名称服务器一起构成一个因特网范围的目录系统的一部分，该系统称为域名系统，用于将助记形式的地址转换成相应的位模式形式。具体来说，当一个人请求将一份报文发送到以助记形式标识的一个目的地时，
DNS is used to convert that mnemonic address into its equivalent IP address that is compatible with the Internet software. The process of extracting
information from DNS is often referred to as a \"DNS lookup.\" Normally, a DNS lookup is completed in a fraction of a second.
域名系统被用于将该助记地址转换成与因特网软件兼容的相应IP地址。从域名系统提取信息的过程常常被称为“域名系统查找”。一般来说，完成一个域名系统查找只需要几分之一秒。
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