ISO 18202:2015 defines, in an abstract manner, the MAL in terms of:
a) the concepts that it builds upon,
b) the basic types it provides,
c) the message headers required by the layer,
d) the relationship between, and the valid sequence of, the messages and resulting behaviours.

It does not specify:
a) individual implementations or products,
b) the implementation of entities or interfaces within real systems,
c) the methods or technologies required for communications.