Hardware and software data communication systems.
The OSI seven layer model attempts to provide a way of partitioning any computer network into independent modules from the lowest (physical) layer to the highest (application) layer. Many different specifications exist at each of these layers.
Networks are often also classified according to their geographical extent: local area network (LAN), metropolitan area network (MAN), wide area network (WAN) and also according to the protocols used.
See BITNET, Ethernet, Internet, Novell, PSTN, network, the.
[Tanenbaum, A., "Computer Networks; 2nd ed.", Prentice Hall, Englewood Cliffs, NJ, 1989.]