IEC 62541-4:2015

OPC Unified Architecture - Part 4: Services

IEC 62541-4:2015 defines the OPC Unified Architecture (OPC UA) Services. The Services described are the collection of abstract Remote Procedure Calls (RPC) that are implemented by OPC UA Servers and called by OPC UA Clients. This second edition cancels and replaces the first edition published in 2011. It constitutes a technical revision. It includes the following changes:
- Update for 6.4 Redundancy.
- Clarifications for Publish and Reconnect scenarios.
- Handling of MonitoredItem changes in short network interruption scenarios.
- Update for 6.1.3 Determining if a Certificate is Trusted.
- Revised definition of parameters semaphoreFile and isOnline in Service RegisterServer.
- Services ModifySubscription and ModifyMonitoredItems.

Architecture Unifiée OPC - Partie 4: Services

L'IEC 62541-4:2015 définit les Services de l'Architecture Unifiée OPC (OPC UA). Les Services décrits sont le recueil d'appels de procédures abstraites distantes (RPC - Remote Procedure Calls) qui sont mises en oeuvre par les Serveurs OPC UA et qui sont appelées par les Clients OPC UA. Cette deuxième édition annule et remplace la première édition parue en 2011. Elle constitue une révision technique. Cette édition inclut les modifications suivantes:
- Mise à jour de 6.4 Redondance.
- Clarifications pour les scénarios Publish et Reconnect.
- Gestion des modifications de MonitoredItem dans les scénarios de courte interruption du réseau.
- Mise à jour de 6.1.3 Déterminer si un Certificat est fiable.
- Révision de la définition des paramètres semaphoreFile et isOnline dans le Service.
- Services ModifySubscription et ModifyMonitoredItems.

General Information

• Status: Published
• Publication Date: 24-Mar-2015
• ICS: 25.040.40 - Industrial process measurement and control
• ICS: 29.100.10 - Magnetic components
• ICS: 29.180 - Transformers. Reactors
• ICS: 35.100.05 - Multilayer applications
• Technical Committee: SC 65E - Devices and integration in enterprise systems
• Drafting Committee: WG 8 - TC 65/SC 65E/WG 8
• Current Stage: DELPUB - Deleted Publication
• Start Date: 13-Jul-2020
• Completion Date: 29-Sep-2017

Relations

• Revised: IEC 62541-4:2020 - OPC Unified Architecture - Part 4: Services
• Effective Date: 05-Sep-2023
• Revises: IEC 62541-4:2011 - OPC unified architecture - Part 4: Services
• Effective Date: 05-Sep-2023

Overview

IEC 62541-4:2015 is an international standard published by the International Electrotechnical Commission (IEC) that defines the Services of OPC Unified Architecture (OPC UA). OPC UA is a platform-independent, service-oriented architecture designed for industrial automation and interoperability across different systems and vendors. Part 4 specifically details the abstract Remote Procedure Calls (RPCs) that OPC UA servers implement and OPC UA clients invoke.

This edition is a technical revision and update of the original 2011 version. Significant enhancements include improved redundancy handling, enhanced Publish and Reconnect mechanisms, better management of MonitoredItem behavior during short network interruptions, strengthened certificate trust evaluation, and updates to key service operations such as RegisterServer, ModifySubscription, and ModifyMonitoredItems.

By providing a comprehensive specification of OPC UA service sets and behaviors, IEC 62541-4:2015 serves as a foundational document enabling consistent implementation, secure communication, and reliable data exchange within industrial IoT, process control, and manufacturing systems.

Key Topics

• Service Set Model
  Defines the organization of OPC UA services into logical groups such as Discovery, SecureChannel, Session, NodeManagement, View, Query, Attribute, Method, MonitoredItem, and Subscription service sets.

• Request/Response Procedures
  Abstract definitions of the client-server interaction model using request and response messages that facilitate OPC UA services.

• Security and Certificates
  Guidelines and workflows for establishing secure channels, managing application instance certificates, and determining certificate trustworthiness to ensure secure data exchange.

• Redundancy
  Comprehensive framework for server, client, and network redundancy to enhance availability and fault tolerance in OPC UA systems.

• Session and Connection Management
  Procedures for creating, activating, closing sessions, and mechanisms for re-establishing connections after network interruptions.

• Monitoring and Subscription Services
  Services to create, modify, and delete monitored items and subscriptions that allow clients to receive timely notifications of data changes or events.

• Auditing
  Logging and event mechanisms to track security-relevant actions across different service sets to support compliance and troubleshooting.

Applications

IEC 62541-4:2015 is essential for industries requiring robust and interoperable communication architectures such as:

• Industrial Automation
  Enables seamless integration of devices and control systems from multiple vendors by standardizing service operations.

• Smart Manufacturing
  Supports real-time data access, monitoring, and control critical for Industry 4.0 initiatives and advanced manufacturing execution systems (MES).

• Energy and Utilities
  Facilitates secure and reliable data exchange between control centers, substations, and field devices.

• Building Automation
  Provides services for managing HVAC, lighting, and security systems with standardized OPC UA service calls.

• Process Control and Oil & Gas
  Ensures consistent monitoring and control of process variables with fault-tolerant and secure communication services.

By adopting IEC 62541-4:2015, organizations can ensure their OPC UA implementations are compliant with international best practices, improving interoperability, security, and system resilience.

Related Standards

• IEC 62541-1: OPC Unified Architecture - Part 1: Overview and Concepts
  Provides foundational concepts and architecture details complementing Part 4 service definitions.

• IEC 62541-3: OPC Unified Architecture - Part 3: Address Space Model
  Defines the information model OPC UA servers expose, forming the basis for node-related services in Part 4.

• IEC 62541-5: OPC Unified Architecture - Part 5: Information Model
  Specifies structured data models and types used by OPC UA services.

• IEC 62541-6: OPC Unified Architecture - Part 6: Mappings
  Describes the binary and XML mappings which relate to the serialization of the services defined in Part 4.

• IEC 62541-7: OPC Unified Architecture - Part 7: Profiles
  Defines compliance profiles that include specific services from Part 4.

Together, these complementary standards form the comprehensive OPC UA framework supporting secure, interoperable, and scalable industrial communication systems.

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Keywords: IEC 62541-4, OPC UA Services, OPC Unified Architecture, industrial automation standards, OPC UA redundancy, secure OPC UA communication, OPC UA monitoring, industrial interoperability, IEC OPC UA standard, OPC UA session management

Standards Content (Sample)

IEC 62541-4 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
OPC Unified Architecture –
Part 4: Services
Architecture Unifiée OPC –
Partie 4: Services
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IEC 62541-4 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
OPC Unified Architecture –
Part 4: Services
Architecture Unifiée OPC –
Partie 4: Services
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40; 35.100 ISBN 978-2-8322-2369-7

– 2 – IEC 62541-4:2015 © IEC 2015
CONTENTS
FOREWORD . 12
1 Scope . 14
2 Normative references . 14
3 Terms, definitions and conventions . 15
3.1 Terms and definitions . 15
3.2 Abbreviations and symbols . 15
3.3 Conventions for Service definitions . 16
4 Overview . 17
4.1 Service Set model . 17
4.2 Request/response Service procedures . 21
5 Service Sets . 21
5.1 General . 21
5.2 Service request and response header . 21
5.3 Service results . 21
5.4 Discovery Service Set . 23
5.4.1 Overview . 23
5.4.2 FindServers . 24
5.4.3 GetEndpoints . 25
5.4.4 RegisterServer . 28
5.5 SecureChannel Service Set . 31
5.5.1 Overview . 31
5.5.2 OpenSecureChannel . 32
5.5.3 CloseSecureChannel . 35
5.6 Session Service Set . 36
5.6.1 Overview . 36
5.6.2 CreateSession . 36
5.6.3 ActivateSession . 40
5.6.4 CloseSession . 43
5.6.5 Cancel . 43
5.7 NodeManagement Service Set . 44
5.7.1 Overview . 44
5.7.2 AddNodes . 44
5.7.3 AddReferences . 46
5.7.4 DeleteNodes . 47
5.7.5 DeleteReferences . 48
5.8 View Service Set . 49
5.8.1 Overview . 49
5.8.2 Browse . 50
5.8.3 BrowseNext . 52
5.8.4 TranslateBrowsePathsToNodeIds . 54
5.8.5 RegisterNodes . 56
5.8.6 UnregisterNodes . 57
5.9 Query Service Set . 57
5.9.1 Overview . 57
5.9.2 Querying Views . 58
5.9.3 QueryFirst . 58

5.9.4 QueryNext . 62
5.10 Attribute Service Set . 63
5.10.1 Overview . 63
5.10.2 Read . 63
5.10.3 HistoryRead . 65
5.10.4 Write . 67
5.10.5 HistoryUpdate . 69
5.11 Method Service Set . 70
5.11.1 Overview . 70
5.11.2 Call . 71
5.12 MonitoredItem Service Set . 73
5.12.1 MonitoredItem model . 73
5.12.2 CreateMonitoredItems . 79
5.12.3 ModifyMonitoredItems . 81
5.12.4 SetMonitoringMode . 83
5.12.5 SetTriggering . 84
5.12.6 DeleteMonitoredItems . 85
5.13 Subscription Service Set . 86
5.13.1 Subscription model . 86
5.13.2 CreateSubscription . 93
5.13.3 ModifySubscription . 94
5.13.4 SetPublishingMode . 95
5.13.5 Publish . 96
5.13.6 Republish . 98
5.13.7 TransferSubscriptions . 98
5.13.8 DeleteSubscriptions . 100
6 Service behaviours . 101
6.1 Security . 101
6.1.1 Overview . 101
6.1.2 Obtaining and Installing an Application Instance Certificate . 101
6.1.3 Determining if a Certificate is Trusted . 102
6.1.4 Creating a SecureChannel . 104
6.1.5 Creating a Session . 106
6.1.6 Impersonating a User . 107
6.2 Software Certificates . 107
6.2.1 Overview . 107
6.2.2 Obtaining and Installing a Software Certificate . 107
6.2.3 Validating a Software Certificate . 109
6.3 Auditing . 109
6.3.1 Overview . 109
6.3.2 General audit logs. 109
6.3.3 General audit Events . 109
6.3.4 Auditing for Discovery Service Set . 110
6.3.5 Auditing for SecureChannel Service Set . 110
6.3.6 Auditing for Session Service Set . 110
6.3.7 Auditing for NodeManagement Service Set . 111
6.3.8 Auditing for Attribute Service Set . 111
6.3.9 Auditing for Method Service Set . 111
6.3.10 Auditing for View, Query, MonitoredItem and Subscription Service Set . 112

– 4 – IEC 62541-4:2015 © IEC 2015
6.4 Redundancy . 112
6.4.1 Redundancy overview . 112
6.4.2 Server redundancy overview . 112
6.4.3 Client redundancy . 116
6.4.4 Network redundancy . 116
6.5 Re-establishing connections . 117
7 Common parameter type definitions . 118
7.1 ApplicationDescription . 118
7.2 ApplicationInstanceCertificate . 118
7.3 BrowseResult . 119
7.4 ContentFilter . 119
7.4.1 ContentFilter structure . 119
7.4.2 ContentFilterResult . 120
7.4.3 FilterOperator . 121
7.4.4 FilterOperand parameters . 127
7.5 Counter . 128
7.6 ContinuationPoint . 129
7.7 DataValue . 129
7.7.1 General. 129
7.7.2 PicoSeconds . 130
7.7.3 SourceTimestamp . 130
7.7.4 ServerTimestamp . 130
7.7.5 StatusCode assigned to a value . 131
7.8 DiagnosticInfo . 131
7.9 EndpointDescription . 132
7.10 ExpandedNodeId . 133
7.11 ExtensibleParameter . 133
7.12 Index . 134
7.13 IntegerId . 134
7.14 MessageSecurityMode . 134
7.15 MonitoringParameters . 134
7.16 MonitoringFilter parameters . 135
7.16.1 Overview . 135
7.16.2 DataChangeFilter . 136
7.16.3 EventFilter . 136
7.16.4 AggregateFilter . 139
7.17 MonitoringMode . 140
7.18 NodeAttributes parameters . 140
7.18.1 Overview . 140
7.18.2 ObjectAttributes parameter . 141
7.18.3 VariableAttributes parameter . 141
7.18.4 MethodAttributes parameter . 142
7.18.5 ObjectTypeAttributes parameter . 142
7.18.6 VariableTypeAttributes parameter . 142
7.18.7 ReferenceTypeAttributes parameter . 143
7.18.8 DataTypeAttributes parameter . 143
7.18.9 ViewAttributes parameter . 143
7.19 NotificationData parameters . 144
7.19.1 Overview . 144

7.19.2 DataChangeNotification parameter . 144
7.19.3 EventNotificationList parameter . 145
7.19.4 StatusChangeNotification parameter . 145
7.20 NotificationMessage . 145
7.21 NumericRange . 146
7.22 QueryDataSet . 147
7.23 ReadValueId . 147
7.24 ReferenceDescription. 148
7.25 RelativePath . 149
7.26 RequestHeader . 149
7.27 ResponseHeader . 151
7.28 ServiceFault . 151
7.29 SessionAuthenticationToken . 151
7.30 SignatureData . 153
7.31 SignedSoftwareCertificate . 153
7.32 SoftwareCertificate . 153
7.33 StatusCode . 154
7.33.1 General. 154
7.33.2 Common StatusCodes . 156
7.34 TimestampsToReturn . 159
7.35 UserIdentityToken parameters . 159
7.35.1 Overview . 159
7.35.2 AnonymousIdentityToken . 160
7.35.3 UserNameIdentityToken . 160
7.35.4 X509IdentityTokens . 161
7.35.5 IssuedIdentityToken . 161
7.36 UserTokenPolicy . 162
7.37 ViewDescription . 163
Annex A (informative) BNF definitions . 164
A.1 Overview over BNF . 164
A.2 BNF of RelativePath . 164
A.3 BNF of NumericRange . 165
Annex B (informative) Content Filter and Query Examples . 166
B.1 Simple ContentFilter examples . 166
B.1.1 Overview . 166
B.1.2 Example 1. 166
B.1.3 Example 2. 167
B.2 Complex Examples of Query Filters . 167
B.2.1 Overview . 167
B.2.2 Used type model . 168
B.2.3 Example Notes . 170
B.2.4 Example 1. 171
B.2.5 Example 2. 172
B.2.6 Example 3. 173
B.2.7 Example 4. 175
B.2.8 Example 5. 176
B.2.9 Example 6. 178
B.2.10 Example 7. 179
B.2.11 Example 8. 181

– 6 – IEC 62541-4:2015 © IEC 2015
B.2.12 Example 9. 182

Figure 1 – Discovery Service Set . 17
Figure 2 – SecureChannel Service Set. 18
Figure 3 – Session Service Set . 18
Figure 4 – NodeManagement Service Set . 18
Figure 5 – View Service Set . 19
Figure 6 – Attribute Service Set . 19
Figure 7 – Method Service Set . 20
Figure 8 – MonitoredItem and Subscription Service Sets . 20
Figure 9 – Discovery process . 23
Figure 10 – Using a Gateway Server . 27
Figure 11 – The Registration Process – Manually Launched Servers . 28
Figure 12 – The Registration Process – Automatically Launched Servers . 29
Figure 13 – SecureChannel and Session Services . 32
Figure 14 – Multiplexing Users on a Session . 38
Figure 15 – MonitoredItem Model . 74
Figure 16 – Typical delay in change detection . 75
Figure 17 – Queue overflow handling . 77
Figure 18 – Triggering Model . 78
Figure 19 – Obtaining and Installing an Application Instance Certificate . 102
Figure 20 – Determining if a Application Instance Certificate is Trusted . 104
Figure 21 – Establishing a SecureChannel . 105
Figure 22 – Establishing a Session . 106
Figure 23 – Impersonating a User . 107
Figure 24 – Obtaining and Installing a Software Certificate . 108
Figure 25 – Transparent Redundancy setup . 113
Figure 26 – Non-Transparent Redundancy setup . 113
Figure 27 – Server proxy for redundancy . 116
Figure 28 – Reconnect Sequence . 117
Figure 29 – Logical layers of a Server . 152
Figure 30 – Obtaining a SessionAuthenticationToken . 152
Figure B.1 – Filter Logic Tree Example . 166
Figure B.2 – Filter Logic Tree Example . 167
Figure B.3 – Example Type Nodes . 169
Figure B.4 – Example Instance Nodes . 170
Figure B.5 – Example 1 Filter . 171
Figure B.6 – Example 2 Filter Logic Tree . 172
Figure B.7 – Example 3 Filter Logic Tree . 174
Figure B.8 – Example 4 Filter Logic Tree . 176
Figure B.9 – Example 5 Filter Logic Tree . 177
Figure B.10 – Example 6 Filter Logic Tree . 178
Figure B.11 – Example 7 Filter Logic Tree . 180

Figure B.12 – Example 8 Filter Logic Tree . 181
Figure B.13 – Example 9 Filter Logic Tree . 183

Table 1 – Service Definition Table . 16
Table 2 – Parameter Types defined in IEC 62541-3 . 17
Table 3 – FindServers Service Parameters . 25
Table 4 – GetEndpoints Service Parameters . 27
Table 5 – RegisterServer Service Parameters . 30
Table 6 – RegisterServer Service Result Codes . 30
Table 7 – OpenSecureChannel Service Parameters . 34
Table 8 – OpenSecureChannel Service Result Codes . 35
Table 9 – CloseSecureChannel Service Parameters . 35
Table 10 – CloseSecureChannel Service Result Codes . 35
Table 11 – CreateSession Service Parameters . 38
Table 12 – CreateSession Service Result Codes . 40
Table 13 – ActivateSession Service Parameters . 42
Table 14 – ActivateSession Service Result Codes . 43
Table 15 – CloseSession Service Parameters . 43
Table 16 – CloseSession Service Result Codes . 43
Table 17 – Cancel Service Parameters . 44
Table 18 – AddNodes Service Parameters . 45
Table 19 – AddNodes Service Result Codes . 45
Table 20 – AddNodes Operation Level Result Codes . 46
Table 21 – AddReferences Service Parameters . 46
Table 22 – AddReferences Service Result Codes . 47
Table 23 – AddReferences Operation Level Result Codes . 47
Table 24 – DeleteNodes Service Parameters . 48
Table 25 – DeleteNodes Service Result Codes . 48
Table 26 – DeleteNodes Operation Level Result Codes . 48
Table 27 – DeleteReferences Service Parameters . 49
Table 28 – DeleteReferences Service Result Codes . 49
Table 29 – DeleteReferences Operation Level Result Codes . 49
Table 30 – Browse Service Parameters . 51
Table 31 – Browse Service Result Codes. 52
Table 32 – Browse Operation Level Result Codes. 52
Table 33 – BrowseNext Service Parameters . 53
Table 34 – BrowseNext Service Result Codes . 53
Table 35 – BrowseNext Operation Level Result Codes . 54
Table 36 – TranslateBrowsePathsToNodeIds Service Parameters . 55
Table 37 – TranslateBrowsePathsToNodeIds Service Result Codes . 55
Table 38 – TranslateBrowsePathsToNodeIds Operation Level Result Codes . 56
Table 39 – RegisterNodes Service Parameters . 56
Table 40 – RegisterNodes Service Result Codes . 57

– 8 – IEC 62541-4:2015 © IEC 2015
Table 41 – UnregisterNodes Service Parameters . 57
Table 42 – UnregisterNodes Service Result Codes . 57
Table 43 – QueryFirst Request Parameters . 60
Table 44 – QueryFirst Response Parameters . 61
Table 45 – QueryFirst Service Result Codes . 62
Table 46 – QueryFirst Operation Level Result Codes . 62
Table 47 – QueryNext Service Parameters . 63
Table 48 – QueryNext Service Result Codes. 63
Table 49 – Read Service Parameters . 64
Table 50 – Read Service Result Codes . 64
Table 51 – Read Operation Level Result Codes . 65
Table 52 – HistoryRead Service Parameters . 66
Table 53 – HistoryRead Service Result Codes . 67
Table 54 – HistoryRead Operation Level Result Codes . 67
Table 55 – Write Service Parameters . 68
Table 56 – Write Service Result Codes . 69
Table 57 – Write Operation Level Result Codes . 69
Table 58 – HistoryUpdate Service Parameters . 70
Table 59 – HistoryUpdate Service Result Codes . 70
Table 60 – HistoryUpdate Operation Level Result Codes . 70
Table 61 – Call Service Parameters . 72
Table 62 – Call Service Result Codes . 72
Table 63 – Call Operation Level Result Codes . 73
Table 64 – CreateMonitoredItems Service Parameters . 80
Table 65 – CreateMonitoredItems Service Result Codes . 80
Table 66 – CreateMonitoredItems Operation Level Result Codes . 81
Table 67 – ModifyMonitoredItems Service Parameters . 82
Table 68 – ModifyMonitoredItems Service Result Codes . 82
Table 69 – ModifyMonitoredItems Operation Level Result Codes . 83
Table 70 – SetMonitoringMode Service Parameters . 83
Table 71 – SetMonitoringMode Service Result Codes . 83
Table 72 – SetMonitoringMode Operation Level Result Codes . 84
Table 73 – SetTriggering Service Parameters . 84
Table 74 – SetTriggering Service Result Codes . 85
Table 75 – SetTriggering Operation Level Result Codes . 85
Table 76 – DeleteMonitoredItems Service Parameters . 85
Table 77 – DeleteMonitoredItems Service Result Codes . 86
Table 78 – DeleteMonitoredItems Operation Level Result Codes . 86
Table 79 – Subscription States . 88
Table 80 – Subscription State Table . 89
Table 81 – State variables and parameters . 91
Table 82 – Functions .
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