IEC 61158-4-21:2010

Overview

IEC 61158-4-21:2010 - part of the IEC 61158 fieldbus series - specifies the data‑link layer protocol (Type 21) for industrial communication networks. It defines procedures and structures for timely transfer of data and control information between peer data‑link user entities and among data‑link entities that form a distributed data‑link service provider. The standard uses the service model of ISO/IEC 8802‑3 (Ethernet MAC), includes provisions for hot‑adding and removing nodes during normal operation, and replaces IEC/PAS 62573 (2008). The bilingual edition (2012‑01) corresponds to the English 2010‑08 publication.

Key topics and technical requirements

• Data‑link services and timing: Procedures to ensure timely delivery of data and control information between DLS‑users and peer entities.
• MAC integration: Definition of communication opportunities and medium access behavior based on ISO/IEC 8802‑3 MAC.
• DLPDU structure & encoding: Detailed formats and encoding rules for Data‑Link Protocol Data Units (DLPDUs) and their physical representation (Version, Length, DST/SRC addresses, Frame Control, Extension, DSAP, etc.).
• Dynamic network management: Mechanisms and procedures for adding/removing nodes during normal operation and managing topology changes.
• Protocol machines & primitives: Specification of the DL‑protocol machine (DLPM), Data‑link Manager (DLM), primitives exchanged with DLS‑users, DMAC and DPHY, and associated parameters and state machines.
• Network control messages: Definitions for NCM messages (e.g., NCM_LA, NCM_AT, NCM_LS, NCM_RS, NCM_AR) used for network management, address and topology control.
• Configuration, constants & error codes: Tables of configuration parameters, constants, device identifiers, and standardized error reporting codes to support conformance and diagnostics.

Applications and who should use it

• Industrial device manufacturers implementing fieldbus data‑link functionality in embedded firmware or NICs.
• Protocol stack developers building compliant data‑link layers or gateways between fieldbus types and Ethernet.
• System integrators and control engineers designing deterministic, real‑time industrial networks for factory automation and process control.
• Test laboratories and conformity assessors verifying interoperability, timing, and protocol conformance.
• Asset/maintenance engineers using network control messages for topology discovery, diagnostics and hot‑swap operations.

Related standards

• ISO/IEC 8802‑3 (Ethernet MAC) - referenced for MAC behavior and medium access.
• IEC 61158 series - other parts define application, transport and physical layers and additional Type elements in the fieldbus family.

Keywords: IEC 61158-4-21, fieldbus, data-link layer, DLPDU, industrial communication, ISO/IEC 8802-3 MAC, fieldbus protocol, industrial networks, protocol conformance, network management.