IEC 61158-4-2:2023

Overview

IEC 61158-4-2:2023 - part of the IEC 61158 fieldbus series - defines the data-link layer protocol specification (Type 2 elements) for industrial communication networks. Edition 5.0 (2023-03) specifies the procedures peer data-link entities (DLEs) must follow to provide reliable data-link services over a physical layer. The document is intended as a development, testing and procurement reference to enable interoperability, support time‑critical communications and guide implementers and system integrators in open automation environments.

Key topics and technical requirements

The standard covers the structure, encoding and operational rules for the data‑link layer without prescribing physical media specifics. Primary topics include:

• DLL architecture and services - functional classes, QoS considerations, and the DLL’s role in the three‑layer fieldbus reference model.
• DLPDU and Lpacket structure - definitions of Data‑Link Protocol Data Units (DLPDUs), Lpacket components and encoding conventions.
• Addressing - MAC ID, generic tag and fixed tag address formats used by DLEs.
• Media access and scheduling - access control machine (ACM), scheduled and unscheduled DLPDU handling, and moderator support.
• Services and procedures - connected and connectionless transfer services, queue maintenance, tag filters, link synchronization, synchronized parameter change and event reporting.
• Time and health mechanisms - time distribution Lpackets, tMinus/link parameters, “I’m‑alive” and ping mechanisms for synchronization and fault detection.
• Special Lpackets - UCMM (UnScheduled Connectionless Message Mode), keeper, TUI, WAMI, IP and Ethernet Lpackets, plus debug/reporting packets.
• DLL–PhL interface - required services and data‑encoding rules assumed from the physical layer.
• Station management objects - object models (e.g., ControlNet™ and Keeper objects), class/instance attributes, services and behavior to support network management, testing and commissioning.
• Conformance and applicability - guidelines for implementers, test houses and procurement to ensure interoperable equipment.

Practical applications and users

IEC 61158-4-2:2023 is used by:

• Device and gateway manufacturers implementing reliable data‑link protocols for field devices and controllers.
• System integrators and automation engineers designing deterministic, time‑critical industrial networks.
• Test laboratories and certification bodies for conformance testing and procurement specifications.
• OEMs and network architects seeking interoperability in multi‑vendor fieldbus environments.
• Standards committees and researchers analyzing fieldbus data‑link behaviors and QoS implications.

Related standards

• IEC 61158 series (other parts defining physical layer, application layer and mapping to the three‑layer fieldbus reference model)
• IEC 61158‑1 (reference models and overview of Type elements)

Keywords: IEC 61158-4-2, fieldbus, data-link layer, industrial communication networks, DLPDU, Lpacket, MAC ID, QoS, time-critical communications, station management.