Most of this original work was sponsored by the U.S. government through the Defense Advanced Research Projects Agency (DARPA--pronounced "DAR-pa"). Over the years, the development of the lnternet shifted from a defense project to an academic research project, and today it is largely a commercial undertaking that links a worldwide combination of WANs, MANs, and LANs involving millions of computers.
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. 5/34 域的建立由互联网名称与数字地址分配机构（ICANN）监管,
Internet Architecture
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.
最初的工作大多是由美国政府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 3/34 台计算机。
Internet Architecture
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 11/34 现出了层次结构（图9A-1）。
Connecting to the Internet
II. Connecting to the lnternet To simplify the process of connecting to the Internet, numerous companies, called Internet service providers (ISPs), allow customers to connect their domains to the Internet via the ISP's equipment or to become a part of a domain already establitecture
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。 9/34
Internet Architecture
If one "stood" at a domain's gateway and "looked out" into the cloud, one could find a variety of structures. Indeed, the lnternet has grown in a somewhat haphazard way as various domains have found points at which to connect to the cloud. One popular structure, however, is for the gateways of a number of domains to be connected to form a regional network of gateways. 支持/赞成，是为了...
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 10/34 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。
Internet Architecture
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 轮流地、依次 to a more global network to which other regional networks attach. In this manner, that portion of the cloud takes on a hierarchical structure (Figure 9A-I).
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 12/34 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 lnternet access for the duration of the telephone call.
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 6/34 公司进行注册。
Internet Architecture
Once a domain has been registered, it can be attached to the existing lnternet by means of a router that connects one of the networks in the domain to a network already in the Internet. This particular router is often referred to as the domain's gateway, in that it represents the domain's gate to the rest of the Internet.
UNIT 9 The Internet
Section A The Internet
Introduction
The most notable example of an internet is the Internet (note the uppercase l ), which originated from research projects going back to the early 1960s. The goal was to develop the ability to link a variety of computer networks so that they could function as a connected system that would not be disrupted by local disasters.
I. Internet Architecture Conceptually, the internet can be viewed as a collection of domains, each of which consists of a network or a relatively small internet operated by a single organization such as a university, company, or government agency. Each domain is an autonomous system that can be configured as the local authority desires.
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 7/34 关，因为它相当于该域通往因特网其余部分的大门。