IEC 61158-6-2:2019

Overview

IEC 61158-6-2:2019 is the international standard that defines the application layer protocol specification for Type 2 fieldbus elements within industrial communication networks. It provides the common elements for both time‑critical and non‑time‑critical messaging between application programs in automation systems. The document specifies externally visible behavior, service primitives, and the wire representation of PDUs in conformance with the OSI Basic Reference Model (ISO/IEC 7498‑1) and the OSI application layer structure (ISO/IEC 9545).

Key Topics

• Application layer protocol (FAL): Abstract and transfer syntax for Fieldbus Application Layer (FAL) PDUs, including UCMM (connectionless) and connection‑oriented transports.
• Service primitives & PDUs: Definition of wire‑representation and externally visible behavior of service primitives and protocol data units (PDUs).
• Connection management: Connection Manager and Connection object behaviors, priorities, remaining path handling, and error codes.
• Object and service definitions: Identity, Assembly, Time Sync, Parameter and other object PDUs with updated class/attribute/service codes.
• State machines: Structured state machines for AP‑Context, FSPM, ARPMs, transport classes and DLL mapping protocol machines.
• DLL mapping & encapsulation: Mapping to data‑link layer (DMPM 1–3), encapsulation abstract syntax, common packet formats and TCP/session encapsulation management.
• Quality of Service & multicast handling: QoS mapping (DSCP / IEEE 802.1D/802.1Q) and IGMP usage for multicast traffic.
• Data types & encoding: Updates to data type dictionaries, compact encoding rules and data type reporting for interoperability.
• Edition 4 (2019) updates: Clarifications and extensions to response PDU formats, connection priority handling, identity/time sync/assembly PDUs, encapsulation syntax, DLL mapping protocol machine 2, and editorial corrections.

Applications

IEC 61158-6-2 is used wherever robust fieldbus application layer protocols are required:

• Factory automation and discrete manufacturing for device-to-device and controller communications.
• Process control systems requiring synchronized time and parameter exchange.
• Time‑critical and safety‑sensitive applications, where missed message windows can lead to equipment or personnel risk.
• Device manufacturers & firmware developers implementing Type 2 fieldbus stacks and PDUs.
• System integrators and network architects designing deterministic industrial Ethernet or fieldbus solutions.
• Compliance & testing labs verifying conformance to application layer behaviors and PDU formats.

Related Standards

• IEC 61158 (Fieldbus series)
• ISO/IEC 7498‑1 (OSI Basic Reference Model)
• ISO/IEC 9545 (OSI application layer structure)
• IEC 61158‑5‑2 (referenced object definitions)

By aligning implementation with IEC 61158-6-2:2019, vendors and integrators ensure interoperable, deterministic application-layer communications for Type 2 fieldbus deployments in industrial environments.