IEC 61158-5-4:2023

Overview

IEC 61158-5-4:2023 - Industrial communication networks – Fieldbus specifications – Part 5-4: Application layer service definition – Type 4 elements - defines the Fieldbus Application Layer (FAL) elements and services used for both time‑critical and non‑time‑critical messaging between application programs in automation systems. The fourth edition (2023) provides common FAL elements and Type 4‑specific material, including an extension for extended APDU size when operating on P‑NET IP networks.

Key topics and technical requirements

• Scope and architecture: Relationship of the FAL to the OSI application layer and other fieldbus entities; architectural diagrams and component summaries.
• FAL structure and concepts: Application entities (AEs), Application Process Objects (APOs), ASEs (Application Service Elements), naming and addressing, AREPs/REPs and gateway/routing behavior.
• Service definitions: Confirmed and unconfirmed FAL service procedures, time‑sequence diagrams, and common service parameters. Tables include REQUEST/RESPONSE parameters and error code mappings.
• Variable ASE: Variable types, constructed/basic variable specifications and variable model class - essential for representing process data and device parameters.
• Application relationship ASE: Class specifications and services for establishing and managing application relationships (AR send/acknowledge, attribute get/set).
• Conformance and normative references: Required references to related ISO/IEC and fieldbus documents and conformance statements.
• Practical details: APDU size considerations (with P‑NET IP extension), service parameter tables, and error handling guidance.

Practical applications

• Ensures interoperable application‑level messaging for industrial devices and controllers across Type 4 fieldbus implementations.
• Supports both time‑critical (defined time windows with safety/availability implications) and non‑time‑critical communications - applicable to process control, manufacturing automation, and systems where timing constraints affect equipment or personnel safety.
• Used for designing and implementing device firmware, protocol stacks, gateways, and runtime software that must conform to Type 4 fieldbus application services.

Who should use this standard

• Automation system architects and network designers
• Device and PLC manufacturers implementing Type 4 fieldbus stacks
• System integrators and OEMs building interoperable fieldbus solutions
• Safety and reliability engineers assessing time‑critical messaging behavior
• Developers of gateways, routers and protocol converters (including P‑NET IP implementations)

Related standards

• IEC 61158 series (other parts for data link, physical and protocol type definitions)
• IEC 61784 series (profile and protocol type combinations; referenced in the foreword)

Keywords: IEC 61158-5-4, fieldbus, application layer service definition, Type 4, industrial communication networks, time‑critical messaging, FAL, APDU, P‑NET IP, ASE, application relationship.