IEC 61158-3-21/FRAGF ED2

Industrial communication networks - Fieldbus specifications - Part 3-21: Data-link layer service definition - Type 21 elements

Scope

IEC 61158-3-21:2019 provides the common elements for basic time-critical messaging communications between devices in an automation environment. The term “time-critical” in this context means the prioritized full-duplex collision-free time-deterministic communication, of which one or more specified actions are required to be completed with some defined level of certainty. Failure to complete specified actions within the required time risks the failure of the applications requesting the actions, with attendant risk to equipment, plant, and possibly human life.
This International Standard defines in an abstract way the externally visible service provided by the Type 21 data-link layer in terms of:
a) the primitive actions and events of the service;
b) the parameters associated with each primitive action and event, and the form that they take; and
c) the interrelationships between these actions and events, and their valid sequences.