protocol layer

networking The software and/or hardware environment of

two or more communications devices or computers in which a

particular network protocol operates. A network

connection may be thought of as a set of more or less

independent protocols, each in a different layer or level.

The lowest layer governs direct host-to-host communication

between the hardware at different hosts; the highest consists

of user application programs. Each layer uses the layer

beneath it and provides a service for the layer above. Each

networking component hardware or software on one host uses

protocols appropriate to its layer to communicate with the

corresponding component (its "peer") on another host. Such

layered protocols are sometimes known as peer-to-peer

protocols.

The advantages of layered protocols is that the methods of

passing information from one layer to another are specified

clearly as part of the protocol suite, and changes within a

protocol layer are prevented from affecting the other layers.

This greatly simplifies the task of designing and maintaining

communication systems.

Examples of layered protocols are TCP/IP's five layer

protocol stack and the OSI seven layer model.

(1997-05-05)