BS EN IEC 61158-4-21:2019

What is BS EN IEC 61158-4-21 – Type 21 protocol about?  

BS EN IEC 61158-4-21 is part of the BS EN IEC 61158 series that has been created to facilitate the interconnection of automation system components. The Data-link layer provides basic time-critical data communications between devices in an automated environment. Type 21 provides priority-based cyclic and acyclic data communication using an internal collision-free, full-duplex dual-port Ethernet switch technology. For wide applications in various automation applications, Type 21 does not restrict the cyclic/acyclic scheduling policy in the DLL. 

BS EN IEC 61158-4-21 describes: 

• Procedures for the timely transfer of data and control information from one data link user entity to a peer user entity, and among the data link entities forming the distributed data link service provider; 
• Procedures for giving communication opportunities based on ISO/IEC/IEEE 8802-3 MAC, with provisions for nodes to be added or removed during normal operation; 
• Structure of the Fieldbus data link protocol data units (DLPDUs) used for the transfer of data and control information by the protocol of this document, and their representation as physical interface data units. 

Who is BS EN IEC 61158-4-21  - Type 21 protocol for? 

BS EN IEC 61158-4-21 on Type 21 protocol is useful for: 

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

Why should you use BS EN IEC 61158-4-21 - Type 21 protocol?  

BS EN IEC 61158-4-21 is produced to facilitate the interconnection of automation system components. It is related to other standards in the set as defined by the “three-layer” Fieldbus reference model described in IEC 61158-1. The data-link protocol provides the data-link service by making use of the services available from the physical layer.  

BS EN IEC 61158-4-21 provides a set of rules for communication expressed in terms of the procedures to be carried out by peer data-link entities (DLEs) at the time of communication. These rules for communication are intended to provide a sound basis for development in order to serve a variety of purposes: 

• As a guide for implementors and designers 
• For use in the testing and procurement of equipment 
• As part of an agreement for the admittance of systems into the open systems environment 
• As a refinement to the understanding of time-critical communications within OSI 

BS EN IEC 61158-4-21 is concerned, in particular, with the communication and interworking of sensors, effectors, and other automation devices. By using BS EN IEC 61158-4-21 together with other standards positioned within the OSI or Fieldbus reference models, otherwise incompatible systems may work together in any combination. Using BS EN IEC 61158-4-21 guidelines, you are in a position to facilitate industrial automation that accelerates productivity. 

What’s changed since the last update?  

BS EN IEC 61158-4-21:2019 supersedes EN 61158-4-21:2012, which is withdrawn. BS EN IEC 61158-4-21:2019 includes some technical changes with respect to EN 61158-4-21:2012. These include: 

• Added Frame control Value, DLM function, and DLL constants 
• Changed NCM_RETRY_RNMS to NCM_CHECK_NET_INTEGRITY_REQ 
• Updated DLM state table 
• Miscellaneous editorial corrections