SIST EN IEC 62541-4:2026

OPC unified architecture - Part 4: Services (IEC 62541-4:2025)

This part of IEC 62541 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 UA-TCP UA-SC UA-Binary. In that case the Services described in this document appear as OPC UA Binary encoded payload, secured with OPC UA Secure Conversation and transported via OPC UA TCP.
Not all OPC UA Servers implement all of the defined Services. IEC 62541-7 defines the Profiles that dictate which Services must be implemented in order to be compliant with a particular Profile.
A BNF (Backus-Naur form) for browse path names is described in Annex A.

OPC Unified Architecture - Teil 4: Dienste (IEC 62541-4:2025)

Architecture unifiée OPC - Partie 4: Services (IEC 62541-4:2025)

IEC 62541-4:2025 est disponible sous forme de IEC 62541-4:2025 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.

L'IEC 62541-4:2025 définit les Services de l'Architecture unifiée OPC (OPC UA). Les Services définis sont le recueil d'appels de procédures abstraites distantes (RPC, Remote Procedure Call) qui sont mises en œuvre par les Serveurs OPC UA et qui sont appelées par les Clients OPC UA. Toutes les interactions entre Clients et Serveurs OPC UA ont lieu par le biais de ces Services. Les Services définis sont dits abstraits, car aucun mécanisme RPC particulier n'est spécifié dans le présent document pour leur mise en œuvre. L'IEC 62541‑6 spécifie un ou plusieurs mécanismes concrets de mapping pour la mise en œuvre. Par exemple, dans l'IEC 62541‑6, l'un des mécanismes de mapping repose sur l'utilisation du profil UA-TCP UA-SC UA-Binary. Dans ce cas, les Services décrits dans le présent document apparaissent comme une charge utile à codage OPC UA Binaire, sécurisé par une Conversation OPC UA sécurisée et transporté par le protocole TPC d'OPC UA. Tous les Serveurs OPC UA ne mettent pas en œuvre tous les Services définis. L'IEC 62541‑7 définit les Profils qui dictent les Services qui doivent être mis en œuvre afin d'être conforme à un Profil particulier. Une BNF (Backus-Naur Form, forme de Backus-Naur) pour les noms de chemins de navigation est décrite à l'Annexe A. Cette quatrième édition annule et remplace la troisième édition parue en 2020. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) ajout de nouvelles définitions au Service d'Appel de Méthode pour autoriser des arguments de Méthode facultatifs;
b) ajout d'une référence au SystemStatusChangeEventType pour les scénarios d'erreur d'élément surveillé par un événement;
c) amélioration de la description générale de la manière de déterminer si un Certificat est fiable;
d) ajout de la prise en charge d'ECC;
e) ajout de revisedAggregateConfiguration à la structure AggregateFilterResult;
f) ajout de la valeur INVALID au type de données d'énumération BrowseDirection;
g) ajout de la valeur INVALID au type de données d'énumération TimestampsToReturn;
h) ajout de définitions qui permettent de s'assurer que la fonctionnalité d'abonnement fonctionne si les files d'attente de retransmission sont facultatives;
i) ajout d'une exigence de symétrie entre les contrôles du client et le contrôle du Certificat du Serveur;
j) ajout d'une précision indiquant que le domaine "local" de niveau supérieur n'est pas ajouté par le serveur dans le certificat et n'est pas vérifié par le client lorsqu'il est retourné par un LDS-ME;
k) ajout d'une définition relative au comportement d'expiration des IssuedIdentityTokens;
l) ajout du code de statut Good_PasswordChangeRequired à ActivateSession;
m) limitation des AdditionalInfos aux serveurs en mode de débogage;
n) ajout d'un nouveau code de statut Bad_ServerTooBusy;
o) ajout d'une définition pour les cas où le certificat du serveur doit être contenu dans la réponse GetEndpoints.

Enotna arhitektura OPC - 4. del: Storitve (IEC 62541-4:2025)

Ta del standarda IEC 62541 določa storitve OPC Unified Architecture (OPC UA). Določene storitve so zbirka abstraktnih oddaljenih klicev postopkov (RPC), ki jih izvajajo strežniki OPC UA in jih kličejo odjemalci OPC UA. Vse interakcije med odjemalci in strežniki OPC UA potekajo prek teh storitev. Določene storitve se štejejo za abstraktne, ker v tem dokumentu ni določen noben poseben mehanizem RPC za izvedbo. IEC 62541-6 določa eno ali več konkretnih preslikav, ki so podprte za izvedbo. Na primer, ena preslikava v IEC 62541-6 je na UA-TCP UA-SC UA-Binary. V tem primeru se storitve, opisane v tem dokumentu, pojavijo kot binarno kodirano breme OPC UA, zavarovano z OPC UA Secure Conversation in preneseno prek OPC UA TCP.
Vsi strežniki OPC UA ne izvajajo vseh določenih storitev. IEC 62541-7 določa profile, ki narekujejo, katere storitve morajo biti izvedene, da so skladne z določenim profilom.
BNF (Backus-Naurova oblika) za imena poti brskanja je opisana v Prilogi A.

General Information

• Status: Published
• Public Enquiry End Date: 30-Mar-2024
• Publication Date: 12-Apr-2026
• ICS: 25.040.40 - Industrial process measurement and control
• ICS: 35.100.05 - Multilayer applications
• ICS: 35.240.50 - IT applications in industry
• Technical Committee: MOV - Measuring equipment for electromagnetic quantities
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 24-Feb-2026
• Due Date: 01-May-2026
• Completion Date: 13-Apr-2026
• Mandate: M/490 - Standardisation mandate to the European Standardisation Organisations (ESOs) to support European Smart Grid deployment
• Ref Project: EN IEC 62541-4:2026 - OPC unified architecture - Part 4: Services

Relations

• Refers: SIST EN IEC 62541-8:2020 - OPC Unified Architecture - Part 8: Data Access (IEC 62541-8:2020)
• Effective Date: 10-Feb-2026
• Refers: SIST EN IEC 62541-12:2020 - OPC Unified Architecture Specification - Part 12: Discovery (IEC 62541-12:2020)
• Effective Date: 10-Feb-2026
• Refers: SIST EN IEC 62541-5:2020 - OPC Unified Architecture - Part 5: Information Model
• Effective Date: 10-Feb-2026
• Refers: SIST EN IEC 62541-6:2020 - OPC Unified Architecture - Part 6: Mappings (IEC 62541-6:2020)
• Effective Date: 10-Feb-2026
• Refers: SIST EN IEC 62541-11:2020 - OPC Unified Architecture - Part 11: Historical Access (IEC 62541-11:2020)
• Effective Date: 10-Feb-2026
• Refers: SIST EN IEC 62541-3:2020 - OPC unified architecture - Part 3: Address Space Model (IEC 62541-3:2020)
• Effective Date: 10-Feb-2026
• Refers: SIST EN IEC 62541-2:2026 - OPC unified architecture - Part 2: Security Model (IEC 62541-2:2026)
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 62541-3:2026 - OPC unified architecture - Part 3: Address space model (IEC 62541-3:2025)
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 62541-18:2025 - OPC unified architecture - Part 18: Role-Based Security (IEC 62541-18:2025)
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 62541-13:2020 - OPC Unified Architecture - Part 13: Aggregates (IEC 62541-13:2020)
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 62541-7:2020 - OPC unified architecture - Part 7: Profiles (IEC 62541-7:2020)
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 62541-11:2026 - OPC Unified Architecture - Part 11: Historical Access (IEC 62541-11:2025)
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 62541-1:2026 - OPC unified architecture - Part 1: Overview and concepts (IEC 62541-1:2025)
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 62541-5:2026 - OPC unified architecture - Part 5: Information model (IEC 62541-5:2026)
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 62541-9:2020 - OPC Unified Architecture - Part 9: Alarms and conditions (IEC 62541-9:2020)
• Effective Date: 03-Feb-2026

Overview

prEN IEC 62541-4:2024 (IEC 62541-4:2025 RLV) defines the OPC Unified Architecture (OPC UA) - Part 4: Services. It specifies the abstract collection of Remote Procedure Calls (RPC) - the Services - that OPC UA Servers implement and OPC UA Clients invoke. These Services cover discovery, secure channels, sessions, node management, browsing, attribute access (Read/Write/History), Method calls, monitored items and subscriptions, query, auditing, redundancy and other runtime behaviours. The edition is a technical revision and is provided as an RLV (Redline Version) that shows changes compared to the previous edition.

Key Topics and Requirements

• Abstract Service definitions: Services are described at an abstract RPC level; concrete encodings and transports (for example OPC UA Binary over UA-TCP with Secure Conversation) are defined in IEC 62541‑6.
• Service Sets: Includes Discovery, SecureChannel, Session, NodeManagement, View/Browse, Attribute, Method, MonitoredItem and Subscription Service Sets, plus Query and auditing behaviours.
• Security & Authorization: Procedures for SecureChannel creation, session establishment, identity tokens, certificate trust checks and continuous security checks are addressed.
• Subscription & Monitoring: Subscription models, Publish/Republish, monitored items and re-establish/republish behaviours (including optional retransmission queue handling).
• Discovery & Endpoints: FindServers, GetEndpoints and registration services; rules for when server certificates must appear in GetEndpoints responses.
• Data and Filters: Content filters, AggregateFilterResult enhancements and support for timestamps, browse path syntax (BNF in Annex A).
• Significant technical changes in this edition (selected):
  • Optional Method arguments for Call service
  • Support for ECC (Elliptic Curve Cryptography)
  • Added INVALID values for BrowseDirection and TimestampsToReturn
  • New status codes: Good_PasswordChangeRequired, Bad_ServerTooBusy
  • Definitions for IssuedIdentityToken expiration behaviour
  • Clarifications on certificate trust, LDS-ME domain handling and retransmission queues
  • Addition of revisedAggregateConfiguration in AggregateFilterResult

Applications and Users

• Designed for implementers and integrators of OPC UA Servers and Clients in industrial automation, IIoT, SCADA, process control and manufacturing systems.
• Useful to system architects, device vendors, cybersecurity engineers, and test labs who need to implement, map, secure or validate OPC UA Services.
• Enables consistent interoperability across industrial devices and enterprise systems by defining required service semantics and error handling.

Related Standards

• IEC 62541‑6: OPC UA concrete mappings (encodings and transports)
• IEC 62541‑7: OPC UA Profiles (which Services are required for a given compliance profile)
• Annex A provides a BNF for browse path names to support path translation and browsing.

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2026
Enotna arhitektura OPC - 4. del: Storitve (IEC 62541-4:2025)
OPC unified architecture - Part 4: Services (IEC 62541-4:2025)
OPC Unified Architecture - Teil 4: Dienste (IEC 62541-4:2025)
Architecture unifiée OPC - Partie 4: Services (IEC 62541-4:2025)
Ta slovenski standard je istoveten z: EN IEC 62541-4:2026
ICS:
25.040.40 Merjenje in krmiljenje Industrial process
industrijskih postopkov measurement and control
35.240.50 Uporabniške rešitve IT v IT applications in industry
industriji
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 62541-4

NORME EUROPÉENNE
EUROPÄISCHE NORM February 2026
ICS 25.040.40; 35.100.05 Supersedes EN IEC 62541-4:2020
English Version
OPC unified architecture - Part 4: Services
(IEC 62541-4:2025)
Architecture unifiée OPC - Partie 4: Services OPC Unified Architecture - Teil 4: Dienste
(IEC 62541-4:2025) (IEC 62541-4:2025)
This European Standard was approved by CENELEC on 2026-01-20. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 62541-4:2026 E

European foreword
The text of document 65E/1053/CDV, future edition 4 of IEC 62541-4, prepared by SC 65E "Devices
and integration in enterprise systems" of IEC/TC 65 "Industrial-process measurement, control and
automation" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2027-02-28
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2029-02-28
document have to be withdrawn
This document supersedes EN IEC 62541-4:2020 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a standardization request addressed to CENELEC by the
European Commission. The Standing Committee of the EFTA States subsequently approves these
requests for its Member States.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 62541-4:2025 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 62541 (series) NOTE Approved as EN IEC 62541 (series)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 62541-1 - OPC Unified Architecture - Part 1: EN IEC 62541-1 -
Overview and concepts
IEC 62541-2 - OPC unified architecture - Part 2: Security EN IEC 62541-2 -
model
IEC 62541-3 - OPC Unified Architecture - Part 3: Address EN IEC 62541-3 -
Space Model
IEC 62541-5 - OPC Unified architecture - Part 5: EN IEC 62541-5 -
Information Model
IEC 62541-6 - OPC unified architecture - Part 6: EN IEC 62541-6 -
Mappings
IEC 62541-7 - OPC Unified Architecture - Part 7: Profiles EN IEC 62541-7 -
IEC 62541-8 - OPC unified architecture - Part 8: Data EN IEC 62541-8 -
access
IEC 62541-9 - OPC Unified Architecture - Part 9: Alarms EN IEC 62541-9 -
and Conditions
IEC 62541-11 - OPC Unified Architecture - Part 11: EN IEC 62541-11 -
Historical Access
IEC 62541-12 - OPC unified architecture - Part 12: EN IEC 62541-12 -
Discovery and global services
IEC 62541-13 - OPC Unified Architecture - Part 13: EN IEC 62541-13 -
Aggregates
IEC 62541-18 - OPC unified architecture - Part 18: Role- EN IEC 62541-18 -
Based Security
Under preparation. Stage at the time of publication: FprEN IEC 62541-2:2025.
Under preparation. Stage at the time of publication: prEN IEC 62541-9:2024.
IEC 62541-4 ®
Edition 4.0 2025-12
INTERNATIONAL
STANDARD
OPC unified architecture -
Part 4: Services
ICS 25.040.40; 35.100.05 ISBN 978-2-8327-0833-0

IEC 62541-4:2025-12(en)
IEC 62541-4:2025 © IEC 2025
CONTENTS
FOREWORD . 13
1 Scope . 16
2 Normative references . 16
3 Terms, definitions, abbreviated terms and conventions . 17
3.1 Terms and definitions . 17
3.2 Abbreviated terms. 19
3.3 Conventions for Service definitions . 19
4 Overview . 20
4.1 Service Set model. 20
4.2 Request/response Service procedures . 23
5 Service Sets. 24
5.1 General . 24
5.2 Service request and response header . 24
5.3 Service results . 24
5.4 Discovery Service Set . 26
5.4.1 Overview . 26
5.4.2 FindServers . 27
5.4.3 FindServersOnNetwork . 29
5.4.4 GetEndpoints. 30
5.4.5 RegisterServer . 33
5.4.6 RegisterServer2 . 35
5.5 SecureChannel Service Set . 37
5.5.1 Overview . 37
5.5.2 OpenSecureChannel . 38
5.5.3 CloseSecureChannel . 42
5.6 Session Service Set . 43
5.6.1 Overview . 43
5.6.2 CreateSession . 43
5.6.3 ActivateSession . 49
5.6.4 CloseSession . 52
5.6.5 Cancel . 53
5.7 NodeManagement Service Set . 54
5.7.1 Overview . 54
5.7.2 AddNodes . 54
5.7.3 AddReferences . 56
5.7.4 DeleteNodes . 58
5.7.5 DeleteReferences . 59
5.8 View Service Set . 61
5.8.1 Overview . 61
5.8.2 Browse . 61
5.8.3 BrowseNext . 63
5.8.4 TranslateBrowsePathsToNodeIds . 65
5.8.5 RegisterNodes . 67
5.8.6 UnregisterNodes . 68
5.9 Query Service Set. 69
5.9.1 Overview . 69
5.9.2 Querying Views . 70
IEC 62541-4:2025 © IEC 2025
5.9.3 QueryFirst . 70
5.9.4 QueryNext . 74
5.10 Attribute Service Set . 76
5.10.1 Overview . 76
5.10.2 Read . 76
5.10.3 HistoryRead . 78
5.10.4 Write . 81
5.10.5 HistoryUpdate. 84
5.11 Method Service Set. 85
5.11.1 Overview . 85
5.11.2 Call . 86
5.12 MonitoredItem Service Set . 89
5.12.1 MonitoredItem model . 89
5.12.2 CreateMonitoredItems . 94
5.12.3 ModifyMonitoredItems . 97
5.12.4 SetMonitoringMode . 99
5.12.5 SetTriggering. 101
5.12.6 DeleteMonitoredItems . 102
5.13 Subscription Service Set . 104
5.13.1 Subscription model. 104
5.13.2 CreateSubscription. 113
5.13.3 ModifySubscription . 114
5.13.4 SetPublishingMode . 116
5.13.5 Publish . 117
5.13.6 Republish . 119
5.13.7 TransferSubscriptions. 120
5.13.8 DeleteSubscriptions . 122
6 Service behaviours . 123
6.1 Security . 123
6.1.1 Overview . 123
6.1.2 Obtaining and installing an Application Instance Certificate . 124
6.1.3 Determining if a Certificate is trusted . 125
6.1.4 Creating a SecureChannel . 128
6.1.5 Creating a Session . 130
6.1.6 Impersonating a User . 131
6.1.7 Continuous security checks . 131
6.2 Authorization Services . 131
6.2.1 Overview . 131
6.2.2 Indirect handshake with an Identity Provider . 132
6.2.3 Direct handshake with an Identity Provider . 132
6.3 Session-less Service invocation . 133
6.3.1 Description . 133
6.3.2 Parameters . 134
6.3.3 Service results . 135
6.4 Software Certificates . 135
6.5 Auditing . 135
6.5.1 Overview . 135
6.5.2 General audit logs . 136
6.5.3 General audit Events . 136
IEC 62541-4:2025 © IEC 2025
6.5.4 Auditing for Discovery Service Set . 136
6.5.5 Auditing for SecureChannel Service Set . 136
6.5.6 Auditing for Session Service Set . 137
6.5.7 Auditing for NodeManagement Service Set . 137
6.5.8 Auditing for Attribute Service Set . 137
6.5.9 Auditing for Method Service Set . 138
6.5.10 Auditing for View, Query, MonitoredItem and Subscription Service Set . 138
6.6 Redundancy . 138
6.6.1 Redundancy overview . 138
6.6.2 Server Redundancy . 139
6.6.3 Client Redundancy . 150
6.6.4 Network Redundancy . 150
6.6.5 Manually forcing failover . 152
6.7 Re-establishing connections . 152
6.8 Durable Subscriptions . 154
7 Common parameter type definitions . 155
7.1 AdditionalParametersType . 155
7.2 ApplicationDescription . 156
7.3 ApplicationInstanceCertificate . 156
7.4 ApplicationType . 157
7.5 BrowseDirection . 157
7.6 BrowseResult . 158
7.7 ContentFilter . 158
7.7.1 ContentFilter structure . 158
7.7.2 ContentFilterResult . 159
7.7.3 FilterOperator . 160
7.7.4 FilterOperand parameters . 168
7.8 Counter . 170
7.9 ContinuationPoint . 170
7.10 DataChangeTrigger. 171
7.11 DataValue . 172
7.11.1 General. 172
7.11.2 PicoSeconds . 172
7.11.3 SourceTimestamp . 172
7.11.4 ServerTimestamp . 173
7.11.5 StatusCode assigned to a value . 173
7.12 DiagnosticInfo . 174
7.13 DiscoveryConfiguration parameters . 175
7.13.1 Overview . 175
7.13.2 MdnsDiscoveryConfiguration . 175
7.14 EndpointDescription . 175
7.15 EphemeralKeyType . 176
7.16 ExpandedNodeId . 176
7.17 ExtensibleParameter . 177
7.18 Index . 177
7.19 IntegerId . 177
7.20 MessageSecurityMode . 178
7.21 MonitoringParameters . 178
7.22 MonitoringFilter parameters . 179
IEC 62541-4:2025 © IEC 2025
7.22.1 Overview . 179
7.22.2 DataChangeFilter . 180
7.22.3 EventFilter . 181
7.22.4 AggregateFilter . 183
7.23 MonitoringMode . 185
7.24 NodeAttributes parameters . 185
7.24.1 Overview . 185
7.24.2 ObjectAttributes parameter . 186
7.24.3 VariableAttributes parameter . 186
7.24.4 MethodAttributes parameter . 187
7.24.5 ObjectTypeAttributes parameter . 187
7.24.6 VariableTypeAttributes parameter . 188
7.24.7 ReferenceTypeAttributes parameter . 188
7.24.8 DataTypeAttributes parameter . 189
7.24.9 ViewAttributes parameter . 189
7.24.10 GenericAttributes parameter . 190
7.25 NotificationData parameters . 190
7.25.1 Overview . 190
7.25.2 DataChangeNotification parameter . 191
7.25.3 EventNotificationList parameter . 192
7.25.4 StatusChangeNotification parameter . 192
7.26 NotificationMessage . 192
7.27 NumericRange . 193
7.28 QueryDataSet . 194
7.29 ReadValueId . 194
7.30 ReferenceDescription . 195
7.31 RelativePath . 196
7.32 RegisteredServer . 197
7.33 RequestHeader . 198
7.34 ResponseHeader . 200
7.35 ServiceFault . 201
7.36 SessionAuthenticationToken . 201
7.37 SignatureData . 202
7.38 SignedSoftwareCertificate . 202
7.39 StatusCode . 203
7.39.1 General. 203
7.39.2 Common StatusCodes . 206
7.40 TimestampsToReturn . 209
7.41 UserIdentityToken parameters . 210
7.41.1 Overview . 210
7.41.2 Token Encryption and Proof of Possession . 210
7.41.3 AnonymousIdentityToken . 215
7.41.4 UserNameIdentityToken . 216
7.41.5 X509IdentityTokens. 217
7.41.6 IssuedIdentityToken . 218
7.42 UserTokenPolicy . 218
7.43 UserTokenType . 219
7.44 VersionTime . 219
7.45 ViewDescription. 220
IEC 62541-4:2025 © IEC 2025
Annex A (informative) Backus-Naur form (BNF) definitions . 221
A.1 Overview over BNF . 221
A.2 BNF of RelativePath . 221
A.3 BNF of NumericRange . 223
Annex B (informative) ContentFilter and Query examples . 224
B.1 Simple ContentFilter examples . 224
B.1.1 Overview . 224
B.1.2 Example 1 . 224
B.1.3 Example 2 . 225
B.2 Complex Examples of Query Filters . 226
B.2.1 Overview . 226
B.2.2 Used type model . 226
B.2.3 Example Notes . 229
B.2.4 Example 1 . 230
B.2.5 Example 2 . 231
B.2.6 Example 3 . 232
B.2.7 Example 4 . 235
B.2.8 Example 5 . 236
B.2.9 Example 6 . 237
B.2.10 Example 7 . 239
B.2.11 Example 8 . 241
B.2.12 Example 9 . 242
Bibliography . 245

Figure 1 – Discovery Service Set . 21
Figure 2 – SecureChannel Service Set . 21
Figure 3 – Session Service Set . 21
Figure 4 – NodeManagement Service Set . 21
Figure 5 – View Service Set. 22
Figure 6 – Attribute Service Set . 22
Figure 7 – Method Service Set . 23
Figure 8 – MonitoredItem and Subscription Service Sets . 23
Figure 9 – Discovery process . 26
Figure 10 – Using a Gateway Server . 32
Figure 11 – The Registration Process – Manually Launched Servers . 33
Figure 12 –The Registration Process – Automatically Launched Servers . 34
Figure 13 – SecureChannel and Session Services . 38
Figure 14 – Multiplexing users on a Session . 45
Figure 15 – MonitoredItem model . 89
Figure 16 – Typical delay in change detection . 91
Figure 17 – Queue overflow handling . 92
Figure 18 – Triggering model . 93
Figure 19 – Obtaining and installing an Application Instance Certificate . 125
Figure 20 – Determining if an Application Instance Certificate is trusted . 128
Figure 21 – Establishing a SecureChannel . 129
Figure 22 – Establishing a Session . 130
IEC 62541-4:2025 © IEC 2025
Figure 23 – Impersonating a User . 131
Figure 24 – Indirect handshake with an Identity Provider . 132
Figure 25 – Direct handshake with an Identity Provider . 133
Figure 26 – Transparent Redundancy setup example . 140
Figure 27 – Non-Transparent Redundancy setup . 141
Figure 28 – Client Start-up steps . 145
Figure 29 – Cold Failover . 146
Figure 30 – Warm Failover . 147
Figure 31 – Hot Failover . 148
Figure 32 – HotAndMirrored Failover . 149
Figure 33 – Server proxy for Redundancy . 150
Figure 34 – Transparent network Redundancy . 151
Figure 35 – Non-transparent network Redundancy . 152
Figure 36 – Reconnect sequence . 153
Figure 37 – Logical layers of a Server . 201
Figure 38 – Obtaining a SessionAuthenticationToken . 202
Figure 39 – EncryptedSecret layout . 212
Figure B.1 – Filter logic tree example . 224
Figure B.2 – Filter logic tree example . 225
Figure B.3 – Example Type Nodes . 228
Figure B.4 – Example Instance Nodes . 229
Figure B.5 – Example 1 Filter . 230
Figure B.6 – Example 2 filter logic tree . 232
Figure B.7 – Example 3 filter logic tree . 233
Figure B.8 – Example 4 filter logic tree . 235
Figure B.9 – Example 5 filter logic tree . 236
Figure B.10 – Example 6 filter logic tree . 238
Figure B.11 – Example 7 filter logic tree . 240
Figure B.12 – Example 8 filter logic tree . 242
Figure B.13 – Example 9 filter logic tree . 243

Table 1 – Service definition table . 19
Table 2 – Parameter Types defined in IEC 62541-3 . 20
Table 3 – FindServers Service Parameters . 28
Table 4 – FindServersOnNetwork Service Parameters. 29
Table 5 – GetEndpoints Service Parameters . 32
Table 6 – RegisterServer Service Parameters . 34
Table 7 – RegisterServer Service Result Codes . 35
Table 8 – RegisterServer2 . 36
Table 9 – RegisterServer2 Service Result Codes . 36
Table 10 – RegisterServer2 Operation Level Result Codes . 37
Table 11 – OpenSecureChannel Service Parameters . 40
Table 12 – OpenSecureChannel Service Result Codes. 42
IEC 62541-4:2025 © IEC 2025
Table 13 – CloseSecureChannel Service Parameters . 43
Table 14 – CloseSecureChannel Service Result Codes . 43
Table 15 – CreateSession Service Parameters . 46
Table 16 – CreateSession Service Result Codes . 48
Table 17 – ActivateSession Service Parameters . 50
Table 18 – ActivateSession Service Result Codes . 52
Table 19 – CloseSession Service Parameters . 53
Table 20 – CloseSession Service Result Codes . 53
Table 21 – Cancel Service Parameters . 53
Table 22 – AddNodes Service Parameters . 54
Table 23 – AddNodes Service Result Codes . 55
Table 24 – AddNodes Operation Level Result Codes . 56
Table 25 – AddReferences Service Parameters . 56
Table 26 – AddReferences Service Result Codes . 57
Table 27 – AddReferences Operation Level Result Codes . 57
Table 28 – DeleteNodes Service Parameters. 58
Table 29 – DeleteNodes Service Result Codes . 59
Table 30 – DeleteNodes Operation Level Result Codes . 59
Table 31 – DeleteReferences Service Parameters . 59
Table 32 – DeleteReferences Service Result Codes . 60
Table 33 – DeleteReferences Operation Level Result Codes. 60
Table 34 – Browse Service Parameters . 61
Table 35 – Browse Service Result Codes . 63
Table 36 – Browse Operation Level Result Codes . 63
Table 37 – BrowseNext Service Parameters . 64
Table 38 – BrowseNext Service Result Codes . 64
Table 39 – BrowseNext Operation Level Result Codes . 65
Table 40 – TranslateBrowsePathsToNodeIds Service Parameters . 66
Table 41 – TranslateBrowsePathsToNodeIds Service Result Codes . 67
Table 42 – TranslateBrowsePathsToNodeIds Operation Level Result Codes . 67
Table 43 – RegisterNodes Service Parameters . 68
Table 44 – RegisterNodes Service Result Codes . 68
Table 45 – UnregisterNodes Service Parameters . 69
Table 46 – UnregisterNodes Service Result Codes . 69
Table 47 – QueryFirst Request Parameters . 71
Table 48 – QueryFirst Response Parameters . 73
Table 49 – QueryFirst Service Result Codes . 74
Table 50 – QueryFirst Operation Level Result Codes . 74
Table 51 – QueryNext Service Parameters . 75
Table 52 – QueryNext Service Result Codes . 75
Table 53 – Read Service Parameters . 76
Table 54 – Read Service Result Codes . 77
Table 55 – Read Operation Level Result Codes . 77
IEC 62541-4:2025 © IEC 2025
Table 56 – HistoryRead Service Parameters . 78
Table 57 – HistoryRead Service Result Codes . 80
Table 58 – HistoryRead Operation Level Result Codes . 81
Table 59
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