BS EN IEC 61158-3-21:2019

What is BS EN IEC 61158-3-21 - fieldbus type 21 elements about?  

BS EN IEC 61158-3-21 is part of the BS EN IEC 61158 series that has been created to facilitate the interconnection of automation system components. BS EN IEC 61158-3-21 is related to other standards in the set as defined by the “three-layer” Fieldbus reference model described in IEC 61158-1. Throughout the set of Fieldbus standards, the term “service” refers to the abstract capability provided by one layer of the OSI Basic Reference Model to the layer immediately above. The data-link layer service defined in BS EN IEC 61158-3-21 is a conceptual architectural service, independent of administrative and implementation divisions. 

The principal objective of BS EN IEC 61158-3-21 is to specify the characteristics of conceptual services suitable for time-critical communications and to supplement the OSI Basic Reference Model in guiding the development of data link protocols for time-critical communications. A secondary objective is to provide migration paths from previously existing industrial communications protocols. 

Who is BS EN IEC 61158-3-21 - fieldbus type 21 elements for? 

BS EN IEC 61158-3-21 on Industrial communication networks - Fieldbus type 21 elements is useful for: 

• The IT industry / Software programmers 
• Internet engineering task forces  
• The automation industry 
• Implementors and designers of industrial automation systems 

Why should you use BS EN IEC 61158-3-21 - fieldbus type 21 elements?  

BS EN IEC 61158-3-21 provides you with 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. 

BS EN IEC 61158-3-21 defines in an abstract way the externally visible service provided by the Type 21 data-link layer in terms of: 

• The primitive actions and events of the service 
• The parameters associated with each primitive action and event, and the form that they take; and the interrelationships between these actions and events, and their valid sequences 

The purpose of BS EN IEC 61158-3-21 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 

BS EN IEC 61158-3-21 may be used as the basis for formal data link programming interfaces. Nevertheless, BS EN IEC 61158-3-21  is not a formal programming interface, and any such interface will need to address implementation issues not covered by this document, including: 

• The sizes and octet ordering of various multi-octet service parameters; 
• The correlation of paired primitives for request and confirm, or indication and response. 

What’s changed since the last update?  

BS EN IEC 61158-3-21 supersedes EN 61158-3-21:2012, which is withdrawn. BS EN IEC 61158-3-21 includes some technical changes with respect to EN 61158-3-21:2012.  

These include: 

• Added network control message type 
• Miscellaneous editorial corrections 

Using BS EN IEC 61158-3-21 guidelines you are in a position to facilitate industrial automation that accelerates productivity.