Internet Core Protocols: The Definitive Guide

The Internet, Defined

Simply having a lot of interconnected networks does not by itself mean that you have the “Internet.” To “internet” (with a lowercase “i”) means to interconnect networks. You can create an internet of Macintosh networks using AppleTalk and some routers, for example. The term “Internet” (with a capital “I”) refers to the specific global network of TCP/IP-based systems, originally consisting of ARPAnet and the other research networks.

There have been lots of private and public networks that have offered a multi-layer network design (private SNA^[1] networks from the 1980s are a good example of this). Therefore, the Internet in particular is a collection of networks that support host-to-host communications using TCP/IP protocols.

Under this definition, the network is made up of intelligent end-point systems that are self-deterministic, allowing each end-point system to communicate with any host it chooses. Rather than being a network where communications are controlled by a central authority (as found in many private networks), the Internet is specifically meant to be a collection of autonomous hosts that can communicate with each other freely.

This is an important distinction, and one that is often overlooked. For example, many of the private networks have offered mail-delivery services for their customers, allowing a user on one network to send email to another user on another network, but only by going through a predefined mail gateway service. Conversely, the Internet ...