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.