IEC 61158-6-21:2010

Overview

IEC 61158-6-21:2010 is an international standard developed by the International Electrotechnical Commission (IEC) as part of the wider IEC 61158 series, focusing on industrial communication networks and fieldbus specifications. Specifically, Part 6-21 defines the application layer protocol specification for Type 21 elements. This standard forms a vital component in facilitating interoperability and reliable communication among automation system components, particularly those requiring both time-critical and non-time-critical messaging.

The standard aligns with core concepts from the OSI Basic Reference Model (ISO/IEC 7498-1) and the OSI application layer structure (ISO/IEC 9545), ensuring compliance with established international communication frameworks. It describes the protocol governing communication at the application layer, including data representation (wire format) and the externally visible behavior of application protocol data units (APDUs) during data transfer.

IEC 61158-6-21:2010 is essential for system designers, implementers, and integrators seeking standardized methods for industrial device communication, enabling robust and interoperable industrial automation solutions.

Key Topics

• Type 21 Application Layer Protocol: Defines the syntax, behavior, and encoding rules for Type 21 fieldbus communication.
• Interoperability: Facilitates interaction among diverse automation devices such as sensors and actuators, even from different manufacturers.
• Application Protocol Data Units (APDUs): Specifies the formal abstract syntax and transfer syntax for how APDUs are represented and handled.
• Supporting Time-Critical Communications: Addresses requirements for communications that must occur within defined time windows to support safety and process reliability.
• Externally Visible Behavior: Clearly defines how application layer services behave during data exchange.
• Migration Path: Provides mechanisms for transitioning from legacy industrial communication protocols to modern standardized solutions.
• Conformance: Sets criteria for implementing the protocol within products and systems while accommodating flexibility in implementation.
• Terminology and Abbreviations: Adopts definitions from relevant ISO/IEC standards to ensure consistency across industrial communication documentation.

Applications

IEC 61158-6-21:2010 finds practical use in a wide variety of industrial automation environments, including:

• Process Automation: Enables reliable, deterministic communications between controllers, field devices, and supervisory systems in manufacturing plants.
• Distributed Control Systems (DCS): Provides standardized communication between distributed devices, improving system integration and expandability.
• Time-sensitive Operations: Supports applications where failure to communicate within strict timelines could pose risks to plant equipment or human safety.
• Multi-Vendor Environments: Ensures that devices from different manufacturers, adhering to this standard, can work together seamlessly.
• Testing and Procurement: Offers a reference for testing conformance and specifying requirements in procurement processes for industrial communication equipment.
• Legacy System Upgrades: Facilitates the integration and migration of older fieldbus technologies to contemporary, standards-based industrial networks.

Related Standards

Integrating IEC 61158-6-21:2010 within an industrial automation solution often involves coordination with related standards, notably within the IEC 61158 series and OSI model specifications:

• IEC 61158-3-21:2010 - Data-link layer service definition for Type 21 elements
• IEC 61158-4-21:2010 - Data-link layer protocol specification for Type 21 elements
• IEC 61158-5-21:2010 - Application layer service definition for Type 21 elements
• IEC/TR 61158-1 - Fieldbus reference model foundational guidance
• ISO/IEC 7498-1 - The OSI Basic Reference Model
• ISO/IEC 9545 - OSI application layer structure
• IEC 61784 series - Profiles for industrial communication networks
• ISO/IEC 8822, 8824-1, 10731, 9899 - Various underpinning OSI definitions and programming standards

Summary

IEC 61158-6-21:2010 delivers a robust, international framework for designing fieldbus application layers in industrial communication networks, simplifying device interconnection, enhancing safety, and promoting open, interoperable automation systems. For those working with fieldbus systems, understanding and applying this standard is central to developing future-proof and reliable industrial communications infrastructure.