This part of IEC 61158 provides basic time-critical messaging communications between devices in an automation environment. The term time-critical is used to represent the presence of a time-window, within which one or more specified actions are required to be
completed with some defined level of certainty. Failure to complete specified actions within the time window risks failure of the applications requesting the actions, with attendant risk to
equipment, plant and possibly human life.
This part of IEC 61158 defines in an abstract way the externally visible service provided by the Fieldbus 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 which they take; and
c) the interrelationship between these actions and events, and their valid sequences. The purpose of this part of IEC 61158 is to define the services provided to
1) the various types of Fieldbus Application Layer at the boundary between the Application and Data Link Layers of the Fieldbus Reference Model, and
2) Systems Management at the boundary between the Data Link Layer and Systems Management of the Fieldbus Reference Model.
Seven distinct types of services are defined in this part of IEC 61158; each has a corresponding protocol in IEC 61158-4. The seven distinct types of DL-service are: Type 1 A DL-service which provides a superset of those services expected of OSI Data Link
Protocols as specified in ISO/IEC 8886. Type 2 A DL-service which provides both a connected and a connectionless subset of those
services specified in ISO/IEC 8886. Type 3 A DL-service which provides a connectionless subset of those services specified in
ISO/IEC 8886. Type 4 A DL-service which provides a connectionless subset of those services specified in ISO/IEC 8886.
NOTE 1 This part of IEC 61158 does not define a Type 5 Data Lin (...abbreviated)