Overview
IEC 61158-5-18:2010 - "Industrial communication networks – Fieldbus specifications – Part 5-18" - defines the Application Layer service for Type 18 fieldbus systems. It specifies the abstract structure and externally visible services of the Fieldbus Application Layer (FAL) in conformance with the OSI Basic Reference Model (ISO/IEC 7498) and OSI Application Layer Structure (ISO/IEC 9545). Edition 2.0 (2010) is a technical revision of the 2007 edition and includes editorial corrections and the addition of cyclic data segmenting.
Key topics and technical requirements
- Abstract FAL model: Defines application resources (objects/APOs), Application Service Elements (ASEs), and a Layer Management Entity (LME) that together make up the FAL Application Entity (AE).
- Service definition: Specifies primitives (requests/indications/confirmations/responses), service parameters and valid sequences for operations between application programs.
- Time-critical and non-time-critical messaging: Tailored for basic time-critical communications, with attention to deterministic behavior and time windows required by control applications.
- Object-oriented elements: ASEs operate on classes of application process objects (APOs); a management ASE provides services for FAL class instances.
- Protocol-agnostic abstraction: The standard defines conceptual services, not concrete APIs or wire formats - implementation details like octet ordering and request-response correlation are left to protocols and APIs.
- Included service examples: Service families documented include attribute access (Get/Set Attributes), connection management (Connect/Disconnect), cyclic scanning (Start/Stop scan) and verification services (e.g., Verify slave configuration).
- Conformance model: Equipment does not directly “conform” to this part; conformance is achieved by implementing application-layer protocols (see IEC 61158-6 profiles) that fulfil the Type 18 FAL services.
Practical applications
- Designing and standardizing fieldbus application-layer protocols for industrial automation.
- Implementing time-critical control communications in PLCs, I/O modules, robots and process-control systems where determinism is required.
- Creating device firmware, gateway and stack implementations that map FAL services to lower-layer data-link and physical protocols.
- Supporting migration or integration of legacy industrial protocols into Type 18-conformant systems.
Who should use this standard
- Fieldbus protocol designers and implementers
- Device manufacturers and firmware developers
- System integrators and automation architects
- Control-engineering teams specifying deterministic communication requirements
Related standards
- IEC 61158 series (Fieldbus specifications)
- IEC/TR 61158-1 (Overview and guidance)
- ISO/IEC 7498 (OSI Basic Reference Model)
- ISO/IEC 9545 (OSI Application Layer Structure)
This standard is essential when you need an OSI-conformant, object-oriented application-layer service definition for Type 18 fieldbus networks-especially for time-critical industrial communications and cyclic data handling.