Layer

In telecommunications, the term layer has the following meanings:

1. In radio wave propagation, see F region.

2. In telecommunications networks and open systems architecture, a group of related functions that are performed in a given level in a hierarchy of groups of related functions.

Note: In specifying the functions for a given layer, the assumption is made that the specified functions for the layers below are performed, except for the lowest layer.

Source: from Federal Standard 1037C