The next step beyond newspapers (plus magazines and scientific journals) is the on-line digital library. Many professional organizations, such as the ACM (www.acm.org) and the IEEE Computer Society (www.computer.org), already have many journals and conference proceedings on-line. Other groups are following rapidly. Depending on the cost, size, and weight of book-sized notebook computers, printed books may become obsolete. Skeptics should take note of the effect the printing press had on the medieval illuminated manuscript.
报纸（还有杂志和科学期刊）在线形式的下一步是在线的数字化图书馆。许多专业机构，如，ACM (www.acm.org)和IEEE计算机社区(www.computer.org)，已经有很多在线期刊和在线会议论文。其他一些团体也跟着迅速发展起来。凭借书本大小的笔记本电脑在成本、大小及重量方面的优势，打印的书籍将逐步被淘汰。对此持怀疑态度的人应该注意到，印刷机对于中世纪手抄业带来的影响其实也是与此类似的一种发展。

All of the above applications involve interactions between a person and a remote database full of information. The second broad category of network use is person-to-person communication, basically the 21st century's answer to the 19th century's telephone. E-mail is already used on a daily basis by millions of people all over the world and its use is growing rapidly. It already routinely contains audio and video as well as text and pictures. Smell may take a while.
以上提到的计算机网络的应用都涉及个人与富含信息资源的远程数据库之间的交互作用。计算机网络应用的第二大类是人与人之间的通信，基本上是用21世纪新的通信方式回应19世纪的电话。E－mail已经成为全世界数百万人每天基本的通信方式，并且它的使用将得到进一步的快速普及。电子邮件现在不仅有文本和图象，还有音频和视频。（下面再进一步介绍）

Any teenager worth his or her salt is addicted to instant messaging. This facility, derived from the UNIX talk program in use since around 1970, allows two people to type messages at each other in real time. A multiperson version of this idea is the chat room, in which a group of people can type messages for all to see.
青少年把他们的兴趣沉溺在即时消息（instant messaging）上面。这种便捷方式起源于1970年左右UNIX的talk 程序，它可以让两个人即时互发键入的消息。即时消息的多人互发方式是在一个聊天室（chat room）内，一组人都可以键入让所有人看到的消息。

Worldwide newsgroups, with discussions on every conceivable topic, are already commonplace among a select group of people, and this phenomenon will grow to include the population at large. These discussions, in which one person posts a message and all the other subscribers to the newsgroup can read it, run the gamut from humorous to impassioned. Unlike chat rooms, newsgroups are not real time and messages are saved so that when someone comes back from vacation, all messages that have been posted in the meanwhile are patiently waiting for reading.
全球范围内的新闻组，在选出的一群媒体人之间讨论每个想了解的话题，已经是很平常的事，并且这种现象得到进一步的普及。在这些讨论中，每个人都可以发送消息，所有其他订了改组新闻的用户都可以看到这些发送的消息，包括从幽默的小事到充满激情的大事，无所不及。与聊天室不同的是，新闻组的消息不是即时的，这些消息通常保存着以便一些人度假回来时可以来看看。所有的消息发送的同时也在耐心的等待它们的读者。

Another type of person-to-person communication often goes by the name of peer-to-peer communication, to distinguish it from the client-server model (Parameswaran et al., 2001). In this form, individuals who form a loose group can communicate with others in the group, as shown in Fig. 1-3. Every person can, in principle, communicate with one or more other people; there is no fixed division into clients and servers.
另外一种人际通信的方式通常称为对等交流，以区别于客户－服务器模型（Parameswaran et al., 2001）。在这种模式中，单独的个体形成松散的组，这些个体可以和其他的组进行交流，如图1-3所示。原则上，每个人可以和一个或多个人进行交流；这种模式下，客户和服务器没有固定的角色分类。