IEC 61158-5-26:2019

Overview - IEC 61158-5-26:2019 (Type 26 elements)

IEC 61158-5-26:2019 defines the Application Layer service structure for Type 26 fieldbus implementations within the IEC 61158 family. The standard specifies the Fieldbus Application Layer (FAL) in conformance with the OSI Basic Reference Model (ISO/IEC 7498-1) and the OSI Application Layer Structure (ISO/IEC 9545). It describes FAL application-entities (AEs) composed of object-oriented Application Service Elements (ASEs) and a Layer Management Entity (LME), and defines how ASEs operate on Application Process Object (APO) classes, including a management ASE for instance management.

Key technical topics and requirements

• FAL architecture and conformance
  • AE composition: ASEs + LME; AE services and management responsibilities.
  • Conformance to OSI application-layer models and terminology.
• Data type ASE
  • Formal definitions for FAL data types including fixed-length and string types.
• Communication model
  • Protocol stack overview for Type 26 fieldbus and the role of FAL in that stack.
  • Support for both cyclic data exchange and client/server (message) interactions.
• Cyclic data with Common-Memory (CM)
  • CM allocation and data sharing models that enable deterministic cyclic communication.
• Core ASEs and services
  • Cyclic-data ASE, Message data ASE, Communication load measurement ASE, Network management ASE, AR ASE, General-purpose command server ASE, and others.
  • Service primitives (read/write/send/update), network parameter read/write, logging, transparent/vendor-specific messaging, token/holding-time measurements and performance measurement services.
• Management and diagnostics
  • Node and network management information objects, configuration parameters, reset and status services, and logging/measurement support.

Practical applications and who uses this standard

IEC 61158-5-26 is targeted at designers and implementers of industrial communication systems who need a standardized application layer for Type 26 fieldbus networks:

• Device vendors (fieldbus devices, I/O modules, controllers) implementing FAL ASEs and APO objects.
• System integrators and automation engineers designing deterministic cyclic and message-based data exchange in factory and process automation.
• Network architects and test labs ensuring interoperability, conformance testing and performance measurement (token-holding time, communication load).
• OEMs and integrators deploying Type 26 fieldbus networks requiring standardized network management and diagnostics.

Related standards

• ISO/IEC 7498-1 (OSI Basic Reference Model)
• ISO/IEC 9545 (OSI Application Layer Structure)
• Other parts of IEC 61158 (fieldbus specifications) for link, physical and protocol profiles

Keywords: IEC 61158-5-26, Type 26, Fieldbus, Application Layer, FAL, ASE, LME, common memory, cyclic data, industrial communication networks, fieldbus specifications.