Terminology
Internetworking = the interconnection of separate (and often different) communications networks into an internetwork (or internet, a network of networks)
An internetwork typically concists of a large number of Local Area Networks (LAN), Metropolitan Area Networks (MAN) and Wide Area Networks (WAN) interconnected via routers
The Internet = a global open internetwork
Internet technology can also be used to implement closed corporate networks known as intranets
Two or more interconnected intranets are called an extranet
An internetwork provides only an unreliable connectionless datagram service between any two computers
It is the services and applications implemented in the computers that make the internetwork interesting