IEC 61158-3-20:2014

Overview

IEC 61158-3-20:2014 is an International Electrotechnical Commission (IEC) standard that specifies the data-link layer service definitions for Type 20 fieldbus elements within industrial communication networks. It focuses on defining the abstract services provided by the data-link layer at the boundary with the application layer and systems management, particularly for time-critical messaging communications in automation environments. This standard supports connected and connectionless services aligned with ISO/IEC 8886, enabling reliable, time-sensitive data exchange between devices in industrial automation systems.

Key Topics

• Time-Critical Messaging: The standard addresses communication with strict time-window requirements ensuring actions are completed predictably and reliably, critical in automation for equipment safety and operational integrity.
• Data-Link Layer Services: Defines primitive actions, events, and associated parameters at the data-link layer for Type 20 fieldbus protocols, including request/confirm and indication/response pairs.
• Service Subsets: Specifies both connected and connectionless service options, allowing flexibility in communication management and catering to various automation needs.
• Boundary Definitions: Clarifies the services provided to the application layer and between the data-link layer and system management, promoting a modular and interoperable network stack.
• Abstract Specification: Offers a conceptual model rather than implementation details, serving as a foundation for formal programming interfaces and protocol development without imposing implementation constraints.
• Conformance: Emphasizes that conformity is based on data-link protocol implementations fulfilling the defined services, rather than on direct conformance to this service definition document.

Applications

IEC 61158-3-20:2014 serves crucial roles in industrial automation communication networks, particularly where deterministic and reliable data exchange is required within strict timing constraints. Key applications include:

• Industrial Process Control: Enhancing communication between controllers, sensors, and actuators ensuring timely and accurate control actions.
• Factory Automation: Supporting fieldbus systems that manage real-time machine coordination and safety systems.
• Safety-Critical Systems: Enabling communication frameworks for systems where delayed or failed messages could lead to hazardous situations impacting personnel or equipment.
• Systems Integration: Providing a standardized service layer interface to facilitate multi-vendor interoperability and migration from legacy protocols to modern fieldbus technologies.
• Network Management: Assisting in the design of system management protocols residing between the data-link layer and management layers to ensure network reliability and maintainability.

Related Standards

• IEC 61158 Series: The standard is part of the IEC 61158 family that covers fieldbus communication systems specifications, including physical, data-link, and application layers.
• ISO/IEC 8886: Provides generic definitions of connection-oriented and connectionless services that IEC 61158-3-20 references and adapts for industrial fieldbus use.
• IEC 61784-1 & IEC 61784-2: Define protocol profiles and combinations for industrial communication networks, complementing the service-oriented approach of IEC 61158-3-20.
• ISO/IEC 7498-1: The OSI Basic Reference Model that underpins the layered communication architecture this standard addresses.

By adhering to IEC 61158-3-20:2014, industries can ensure robust, time-sensitive communication services within fieldbus networks, supporting enhanced automation performance, safety, and interoperability. Implementers and system architects benefit from a clear service definition framework that facilitates efficient protocol design and seamless integration of industrial devices.