Interconnected Internetwork

An internetwork is a collection of individual networks connected by intermediate networking devices, that functions as a single large network. Internetworking refers to the industry, products, and procedures that meet the challenge of creating and administering internetworks.

Figure below illustrates some different kinds of network technologies that can be interconnected by routers and other networking devices to create an internetwork.

The first networks were time-sharing networks that used mainframes and attached terminals. Such environments were implemented both IBM. Then Local-area networks (LANs) evolved around the PC revolution. LANs enabled multiple users in a relatively small geographical area to exchange files and messages, as well as access shared resources such as file servers and printers. 

Wide-area networks (WANs) create connectivity of LANs with geographically dispersed users. Some of the technologies used for connecting LANs include T1, T3, ATM, ISDN, ADSL, Frame Relay, radio links, and others.

Internetworking evolved as a solution to three key problems: isolated LANs, duplication of resources, and a lack of network management. Isolated LANs made electronic communication between different offices or departments impossible. Duplication of resources meant that the same hardware and software had to be supplied to each office or department, as did separate support staff. This lack of network management meant that no centralized method of managing and troubleshooting networks existed.