BS EN 61158-3-21:2012 - Page 2

Industrial communication networks. Fieldbus specifications. Data-link layer service definition. Type 21 elements | Status: Withdrawn

1 Scope

1.1 Overview

This part of IEC 61158 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 standard defines in an abstract way the externally visible service provided by the Type 21 data-link layer in terms of:

1. a) the primitive actions and events of the service;
2. b) the parameters associated with each primitive action and event, and the form that they take; and
3. c) the interrelationships between these actions and events, and their valid sequences.

The purpose of this standard is to define the services provided to:

• • The Type 21 application layer at the boundary between the application and DLLs of the fieldbus reference model;
• • Systems management at the boundary between the DLL and the systems management of the fieldbus reference model.