In telecommunication, a n -entity is an active element in the n-th layer of the Open Systems Interconnection--Reference Model (OSI-RM) that (a) interacts directly with elements, i.e. , entities, of the layer immediately above or below the n-th layer, (b) is defined by a unique set of rules, i.e. , syntax, and information formats, including data and control formats, and (c) performs a defined set of functions.
Note 1: The n refers to any one of the 7 layers of the OSI-RM.
Note 2: In an existing layered open system, the n may refer to any given layer in the system.
Note 3: Layers are conventionally numbered from the lowest, i.e., the physical layer, to the highest, so that the n + 1 layer is above the n-th layer and the n- 1 layer is below.
Source: from Federal Standard 1037C
