IEC 62541-4-2025 PDF

Full title and description

IEC 62541-4:2025 — OPC unified architecture - Part 4: Services. Defines the abstract OPC UA Services (the collection of Remote Procedure Calls) used for all interactions between OPC UA Clients and Servers, including discovery, secure channel and session management, node and view operations, attributes, methods, monitoring and subscriptions, history, query, redundancy and auditing. This fourth edition (2025) cancels and replaces the previous (2020) edition and contains technical revisions and clarifications to service behaviour, security, subscription handling and status codes.

Abstract

This standard specifies the abstract service set for the OPC Unified Architecture (OPC UA). It describes service semantics, request/response headers, error and status handling, and behavioural rules for client–server interactions without mandating a particular transport or encoding. Concrete mappings (for example UA‑TCP / UA‑SC / UA‑Binary or WebSocket/HTTPS mappings) are defined in IEC 62541-6. The 2025 edition adds support and clarifications including optional method arguments, ECC support, new status codes and subscription/retransmission behaviour among other updates.

General information

• Status: Published / Current edition (valid).
• Publication date: 16 December 2025.
• Publisher: International Electrotechnical Commission (IEC).
• ICS / categories: 25.040.40; 35.100.05.
• Edition / version: 4.0 (Fourth edition, 2025).
• Number of pages: 502.

Scope

Specifies the abstract definitions and semantics of OPC UA Services that implement client-server interactions. Covers service sets for discovery, secure channels, sessions, node and view manipulation, attribute access, method invocation, subscriptions and monitored items, historical access, query services, redundancy and audit mechanisms. The standard defines required and optional behaviours, status codes, data type enumerations, and normative rules that OPC UA Servers and Clients should follow to achieve interoperability; mappings to encodings and transports are handled in IEC 62541-6.

Key topics and requirements

• Service set model: discovery, SecureChannel, Session, NodeManagement, View, Query, Attribute, Method, MonitoredItem, Subscription and related services.
• Request/response headers, service semantics and error/status code conventions (including new status codes introduced in this edition).
• Certificate and security handling: procedures for creating SecureChannels and guidance on determining whether application certificates are trusted.
• Authentication and identity token behaviour, including expiry semantics for IssuedIdentityTokens.
• Subscription, monitored item and retransmission behaviour; changes to ensure subscription functionality when retransmission queues are optional.
• Method call enhancements: support for optional method arguments and related semantics.
• Addition of ECC (Elliptic Curve Cryptography) support and updates to related security interactions.
• New/clarified enumeration values (e.g., INVALID for BrowseDirection and TimestampsToReturn) and other protocol clarifications.
• Operational clarifications such as restrictions on AdditionalInfo, server busy handling, and requirements for providing server certificates in GetEndpoints responses in specified cases.

Typical use and users

Primary users are OPC UA implementers (software and firmware authors), automation vendors, system integrators, test laboratories and certification bodies. Architects and engineers building industrial automation systems, IIoT gateways, cloud connectors, SCADA/HMI vendors and operations teams will use this standard to ensure interoperable client/server behaviour, consistent security handling, correct subscription and historical access semantics, and compliance with OPC UA profiles.

Related standards

IEC 62541 is a multi-part series for OPC UA. Key related parts include: Part 1 (Overview and concepts), Part 2 (Security Model), Part 3 (Address space model), Part 5 (Information model), Part 6 (Mappings — concrete encodings and transports), Part 7 (Profiles), Part 8 (Data Access), Part 9 (Alarms & Conditions), Part 10 (Programs), Part 11 (Historical Access), Part 12 (Discovery and global services), Part 13 (Aggregates), Part 14 (PubSub) and subsequent parts addressing supplemental information models and application-specific extensions.

Keywords

OPC UA, IEC 62541-4, Services, RPC, SecureChannel, Session, Browse, Attributes, Methods, MonitoredItem, Subscription, History, Query, Certificates, ECC, Interoperability, Industrial Automation.

FAQ

Q: What is this standard?

A: IEC 62541-4:2025 defines the abstract services for the OPC Unified Architecture (OPC UA) — the RPC-like operations used by OPC UA Clients to interact with OPC UA Servers.

Q: What does it cover?

A: It covers the semantics and expected behaviour of discovery, secure channel and session management, node/view operations, attribute access, methods, subscriptions and monitored items, historical access, query, redundancy and auditing. It defines service headers, response semantics and status codes but does not mandate a transport or encoding (those are specified in IEC 62541-6).

Q: Who typically uses it?

A: Software and firmware developers implementing OPC UA Clients and Servers, system integrators, automation vendors, test and certification bodies, solution architects and operators who need to ensure correct and interoperable OPC UA service behaviour.

Q: Is it current or superseded?

A: This is the current (fourth) edition published 16 December 2025; it cancels and replaces the previous edition (2020).

Q: Is it part of a series?

A: Yes — it is Part 4 of the IEC 62541 series (OPC UA). The series includes companion parts that define the overall framework, security model, address space, mappings, information models, profiles and additional application-specific parts.

Q: What are the key keywords?

A: OPC UA, Services, SecureChannel, Session, Subscription, Methods, Attributes, MonitoredItem, History, Query, Certificates, ECC, Interoperability.