Historical
IEC 61158-4-3 Ed. 1.0 en:2007
Industrial communication networks - Fieldbus specifications - Part 4-3: Data-link layer protocol specification - Type 3 elements
"It provides basic time-critical messaging communications between devices in an automation environment. This protocol provides communication opportunities to a pre-selected ""master"" subset of data-link entities in a cyclic asynchronous manner, sequentially to each of those data-link entities. Other data-link entities communicate only as permitted and delegated by those master data-link entities. It includes the following significant changes with respect to the previous edition deletion of the former Type 6 fieldbus, and the placeholder for a Type 5 fieldbus data-link layer, for lack of market relevance; addition of new types of fieldbuses; division of this part into multiple parts numbered."
International Electrotechnical Commission [iec]