N-entity
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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.
The n refers to any one of the 7 layers of the OSI-RM.
In an existing layered open system, the n may refer to any given layer in the system.
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.