IEC 62541-4:2020 PDF

OPC Unified Architecture - Part 4: Services

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Title (English):

IEC 62541-4:2020

OPC Unified Architecture - Part 4: Services

Document status:: Active
Format:: Electronic (PDF)
Number of pages:: 717
Publication date:: July 13, 2020
Edition:: IEC IS 62541 edition 3 version 1
ICS:: 25.040.40

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Description (English):

IEC 62541-4:2020 defines the OPC Unified Architecture (OPC UA) Services. The Services defined are the collection of abstract Remote Procedure Calls (RPC) that are implemented by OPC UA Servers and called by OPC UA Clients. All interactions between OPC UA Clients and Servers occur via these Services. The defined Services are considered abstract because no particular RPC mechanism for implementation is defined in this document. IEC 62541-6 specifies one or more concrete mappings supported for implementation. For example, one mapping in IEC 62541-6 is to XML Web Services. In that case the Services described in this document appear as the Web service methods in the WSDL contract. Not all OPC UA Servers will need to implement all of the defined Services. IEC 62541-7 defines the Profiles that dictate which Services need to be implemented in order to be compliant with a particular Profile This third edition cancels and replaces the second edition published in 2015. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) Added ability to resend all data of monitored items in a Subscription using the ResendData Method. b) Added support for durable Subscriptions (lifetime of hours or days). c) Added Register2 and FindServersOnNetwork Services to support network-wide discovery using capability filters. d) Removed definition of software certificates. Will be defined in a future edition. e) Extended and partially revised the redundancy definition. Added sub-range definitions for ServiceLevel and added more terms for redundancy. f) Added a section on how to use Authorization Services to request user access tokens. g) Added JSON Web Tokens (JWTs) as a new user token. h) Added the concept of session-less service invocation. i) Added a generic structure that allows passing any number of attributes to the AddNodes Service. j) Added requirement to protect against user identity token attacks. k) Added new EncryptedSecret format for user identity tokens.

Technical details

Technical committee: SC 65E - Devices and integration in enterprise systems
SKU: IEC 62541-4:2020

Abstract

Overview

IEC 62541-4:2020 (OPC Unified Architecture - Part 4: Services) defines the OPC UA Services: the abstract Remote Procedure Calls (RPCs) that OPC UA Clients invoke and OPC UA Servers implement. This third edition (2020) replaces the 2015 edition and provides a technical revision of the Service definitions used for all client–server interactions in OPC UA. The document describes Services at an abstract level (no specific transport mandated); concrete mappings (for example to XML Web Services) are specified in IEC 62541-6. Profile requirements that determine which Services are mandatory are defined in IEC 62541-7.

Key topics and technical requirements

Abstract Service model: Defines request/response procedures, Service Sets (Discovery, SecureChannel, Session, NodeManagement, View, Attribute, Subscription, MonitoredItem, Method, Query, etc.), headers, and results.
Security and Authorization: Guidance on SecureChannel and Session creation, user impersonation, and Authorization Services; added mechanisms for obtaining user access tokens and defending against user identity token attacks.
Identity tokens: Adds JSON Web Tokens (JWTs) as a supported user token and introduces a new EncryptedSecret format for user identity tokens.
Subscriptions and monitoring: Enhancements include ResendData to resend monitored-item data, support for durable Subscriptions (long-lived subscriptions across hours/days), and changes to Publish/Republish behavior.
Discovery enhancements: New Register2 and FindServersOnNetwork Services to enable network-wide discovery with capability filters.
Redundancy and reliability: Extended redundancy definitions and additional ServiceLevel sub-ranges to support high-availability server/client configurations.
Session-less invocation: Introduces a model for invoking some Services without creating a full Session.
Node management extension: Generic structure enabling multiple attributes to be passed to the AddNodes Service.
Operational protections: New requirements to protect against token attacks and removal of software certificate definitions (to be re-introduced in a future edition).

Applications and who uses it

OPC UA Server and Client developers use IEC 62541-4 to implement compliant Service behavior, request/response semantics, and security expectations.
System integrators and automation engineers apply the Services model when designing reliable, discoverable, and secure industrial systems.
Vendors of industrial IoT, SCADA, and IIoT platforms adopt the Services to ensure interoperability across devices and systems.
Cybersecurity teams reference the document for secure channel/session practices, token management, and auditing requirements.
Use cases include real-time data access, historical data read/write, device discovery, event monitoring, and multi-vendor interoperability in manufacturing, energy, and process industries.

Related standards

IEC 62541-6 - OPC UA Mappings (concrete transport mappings such as XML Web Services)
IEC 62541-7 - OPC UA Profiles (which Services are required for compliance)
Refer to the broader IEC 62541 (OPC UA) series for additional parts (architecture, information model, security, etc.).

Related standards

Standards mentioned in the description

Abstract

Overview

Key topics and technical requirements

Abstract Service model: Defines request/response procedures, Service Sets (Discovery, SecureChannel, Session, NodeManagement, View, Attribute, Subscription, MonitoredItem, Method, Query, etc.), headers, and results.
Security and Authorization: Guidance on SecureChannel and Session creation, user impersonation, and Authorization Services; added mechanisms for obtaining user access tokens and defending against user identity token attacks.
Identity tokens: Adds JSON Web Tokens (JWTs) as a supported user token and introduces a new EncryptedSecret format for user identity tokens.
Subscriptions and monitoring: Enhancements include ResendData to resend monitored-item data, support for durable Subscriptions (long-lived subscriptions across hours/days), and changes to Publish/Republish behavior.
Discovery enhancements: New Register2 and FindServersOnNetwork Services to enable network-wide discovery with capability filters.
Redundancy and reliability: Extended redundancy definitions and additional ServiceLevel sub-ranges to support high-availability server/client configurations.
Session-less invocation: Introduces a model for invoking some Services without creating a full Session.
Node management extension: Generic structure enabling multiple attributes to be passed to the AddNodes Service.
Operational protections: New requirements to protect against token attacks and removal of software certificate definitions (to be re-introduced in a future edition).

Applications and who uses it

OPC UA Server and Client developers use IEC 62541-4 to implement compliant Service behavior, request/response semantics, and security expectations.
System integrators and automation engineers apply the Services model when designing reliable, discoverable, and secure industrial systems.
Vendors of industrial IoT, SCADA, and IIoT platforms adopt the Services to ensure interoperability across devices and systems.
Cybersecurity teams reference the document for secure channel/session practices, token management, and auditing requirements.
Use cases include real-time data access, historical data read/write, device discovery, event monitoring, and multi-vendor interoperability in manufacturing, energy, and process industries.

Related standards

IEC 62541-6 - OPC UA Mappings (concrete transport mappings such as XML Web Services)
IEC 62541-7 - OPC UA Profiles (which Services are required for compliance)
Refer to the broader IEC 62541 (OPC UA) series for additional parts (architecture, information model, security, etc.).

IEC 62541-4:2020 PDF

Technical details

Abstract

Overview

Key topics and technical requirements

Applications and who uses it

Related standards

Related standards

Abstract

Overview

Key topics and technical requirements

Applications and who uses it

Related standards

Related standards

OPC unified architecture - Part 6: Mappings

OPC unified architecture - Profiles

OPC Unified Architecture - Part 4: Services

OPC unified architecture - Part 2: Security Model (IEC 62541-2:2026)