Internet Core Protocols: The Definitive Guide

The Internet Today

Over time, the ARPAnet evolved into an open “network-of-networks” using TCP/IP, with educational, commercial, and other organizations connected to each other through an interwoven mesh of networks. Today this type of mesh architecture is far less common, replaced by a much more structured hierarchy.

Rather than organizations connecting to each other directly, most organizations now connect to a local network access provider who routes network traffic upwards and outwards to other end-point networks.

Generally speaking, there are only a handful of top-level Internet Service Providers (ISPs), each of which provide major interconnection services around the country or globe. Most of these firms are telecommunications companies that specialize in large-scale networking (such as long-distance providers like MCI WorldCom and Sprint).

Below these top-level carriers are local or regional access providers who offer regional access and lower-speed connection services to end users directly (these mid-level carriers are sometimes referred to as Internet Access Providers, or “IAPs”). This design is represented in Figure 1.3.

Figure 1.3. The hierarchical architecture of the Internet

Visually, the Internet can be thought of as a few major networking companies who provide large-scale “backbone” services around the world, followed by a large number of secondary providers that resell ...