What Is the Internet?

In this book, we’ll use the public Internet, a specific computer network, as our principal vehicle for discussing computer networks and their protocols. But what is the Internet? There are a couple of ways to answer this question. First, we can describe the nuts and bolts of the Internet, that is, the basic hardware and software components that make up the Internet. Second, we can describe the Internet in terms of a networking infrastructure that provides services to distributed applications. Let’s begin with the nuts-and-bolts description, using Figure 1.1 to illustrate our discussion.
在这本书中，我们将使用公共互联网，一个特定的计算机网络，作为我们讨论计算机网络及其协议的主要工具。但是互联网是什么呢？回答这个问题有几种方法。首先，我们可以描述互联网的具体细节，即构成互联网的基本硬件和软件组件。其次，我们可以用一个为分布式应用程序提供服务的网络基础设施来描述互联网。让我们从螺母说明开始，使用图1.1来说明我们的讨论。
1、principal 主要的
2、vehicle 工具
3、nuts
4、 infrastructure 基础设施

1.1.1 A Nuts-and-Bolts Description The Internet is a computer network that interconnects hundreds of millions of computing devices throughout the world. Not too long ago, these computing devices were primarily traditional desktop PCs, Linux workstations, and so-called servers that store and transmit information such as Web pages and e-mail messages. Increasingly, however, nontraditional Internet end systems such as laptops, smartphones, tablets,TVs, gaming consoles, Web cams, automobiles, environmental sensing devices, picture frames, and home electrical and security systems are being connected to the Internet. Indeed, the term computer network is beginning to sound a bit dated, given the many nontraditional devices that are being hooked up to the Internet. In Internet jargon, all of these devices are called hosts or end systems. As of July 2011,
互联网是一个计算机网络，连接全世界数亿计算机设备的连接。不久前，这些计算设备主要是传统的台式电脑、Linux工作站和存储和传输网页和信息等电子邮件的所谓服务器。然而，非传统的互联网终端系统，如笔记本电脑、智能手机、平板电脑、电视、游戏机、网络摄像头、汽车、环境传感设备、相框以及家庭电气和安全系统，正越来越多地连接到互联网上。事实上，考虑到许多非传统的设备正在连接到互联网上，计算机网络这个词开始听起来有点过时了。在互联网术语中，所有这些设备都被称为主机或终端系统。截至2011年7月，
1、jargon 术语
2、enterprise 企业

重点：
网络是由一组具有通信能力的设备互相连接而形成的
1、设备可以是主机（host，有时也称为端系统（end system））
2、也可以是连接设备 如连接其他网络的路由器，将设备连接在一起的交换机、变换数据形式的调制解调器等。 用一台即插即用的路由器连接两台电脑时，我们就组建了一个网络，尽管这个网络很小。