IEC 62541-6:2015

IEC 62541-6 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
OPC unified architecture –
Part 6: Mappings
Architecture unifiée OPC –
Partie 6: Correspondances
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé Fax: +41 22 919 03 00
CH-1211 Geneva 20 info@iec.ch
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing more than 30 000 terms and
Technical Specifications, Technical Reports and other definitions in English and French, with equivalent terms in 15
documents. Available for PC, Mac OS, Android Tablets and additional languages. Also known as the International
iPad. Electrotechnical Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a More than 60 000 electrotechnical terminology entries in
variety of criteria (reference number, text, technical English and French extracted from the Terms and Definitions
committee,…). It also gives information on projects, replaced clause of IEC publications issued since 2002. Some entries
and withdrawn publications. have been collected from earlier publications of IEC TC 37,

77, 86 and CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: csc@iec.ch.
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Catalogue IEC - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
Application autonome pour consulter tous les renseignements
Le premier dictionnaire en ligne de termes électroniques et
bibliographiques sur les Normes internationales,
électriques. Il contient plus de 30 000 termes et définitions en
Spécifications techniques, Rapports techniques et autres
anglais et en français, ainsi que les termes équivalents dans
documents de l'IEC. Disponible pour PC, Mac OS, tablettes
15 langues additionnelles. Egalement appelé Vocabulaire
Android et iPad.
Electrotechnique International (IEV) en ligne.

Recherche de publications IEC - www.iec.ch/searchpub
Glossaire IEC - std.iec.ch/glossary
Plus de 60 000 entrées terminologiques électrotechniques, en
La recherche avancée permet de trouver des publications IEC
en utilisant différents critères (numéro de référence, texte, anglais et en français, extraites des articles Termes et
comité d’études,…). Elle donne aussi des informations sur les Définitions des publications IEC parues depuis 2002. Plus
projets et les publications remplacées ou retirées. certaines entrées antérieures extraites des publications des

CE 37, 77, 86 et CISPR de l'IEC.
IEC Just Published - webstore.iec.ch/justpublished

Service Clients - webstore.iec.ch/csc
Restez informé sur les nouvelles publications IEC. Just
Published détaille les nouvelles publications parues. Si vous désirez nous donner des commentaires sur cette
Disponible en ligne et aussi une fois par mois par email. publication ou si vous avez des questions contactez-nous:
csc@iec.ch.
IEC 62541-6 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
OPC unified architecture –
Part 6: Mappings
Architecture unifiée OPC –
Partie 6: Correspondances
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40; 35.100 ISBN 978-2-8322-2373-4

– 2 – IEC 62541-6:2015 © IEC 2015
CONTENTS
FOREWORD . 7
1 Scope . 9
2 Normative references . 9
3 Terms, definitions, abbreviations and symbols . 11
3.1 Terms and definitions . 11
3.2 Abbreviations and symbols . 11
4 Overview . 12
5 Data encoding . 13
5.1 General . 13
5.1.1 Overview . 13
5.1.2 Built-in Types . 13
5.1.3 Guid . 14
5.1.4 ByteString . 15
5.1.5 ExtensionObject` . 15
5.1.6 Variant . 15
5.2 OPC UA Binary . 16
5.2.1 General. 16
5.2.2 Built-in Types . 16
5.2.3 Enumerations. 25
5.2.4 Arrays . 25
5.2.5 Structures . 25
5.2.6 Messages . 26
5.3 XML . 26
5.3.1 Built-in Types . 26
5.3.2 Enumerations. 33
5.3.3 Arrays . 33
5.3.4 Structures . 33
5.3.5 Messages . 34
6 Message SecurityProtocols . 34
6.1 Security handshake . 34
6.2 Certificates . 35
6.2.1 General. 35
6.2.2 Application Instance Certificate . 36
6.2.3 Signed Software Certificate. 36
6.3 Time synchronization . 37
6.4 UTC and International Atomic Time (TAI) . 37
6.5 Issued User Identity Tokens – Kerberos . 38
6.6 WS Secure Conversation . 38
6.6.1 Overview . 38
6.6.2 Notation . 40
6.6.3 Request Security Token (RST/SCT) . 40
6.6.4 Request Security Token Response (RSTR/SCT) . 41
6.6.5 Using the SCT . 42
6.6.6 Cancelling Security contexts . 42
6.7 OPC UA Secure Conversation . 43
6.7.1 Overview . 43

6.7.2 MessageChunk structure . 43
6.7.3 MessageChunks and error handling . 46
6.7.4 Establishing a SecureChannel . 47
6.7.5 Deriving keys . 48
6.7.6 Verifying Message Security . 49
7 Transport Protocols . 50
7.1 OPC UA TCP . 50
7.1.1 Overview . 50
7.1.2 Message structure . 50
7.1.3 Establishing a connection . 52
7.1.4 Closing a connection. 53
7.1.5 Error handling . 54
7.1.6 Error recovery . 54
7.2 SOAP/HTTP . 56
7.2.1 Overview . 56
7.2.2 XML Encoding . 56
7.2.3 OPC UA Binary Encoding . 57
7.3 HTTPS . 57
7.3.1 Overview . 57
7.3.2 XML Encoding . 59
7.3.3 OPC UA Binary Encoding . 60
7.4 Well known addresses . 60
8 Normative Contracts . 61
8.1 OPC Binary Schema . 61
8.2 XML Schema and WSDL . 61
Annex A (normative) Constants . 62
A.1 Attribute Ids . 62
A.2 Status Codes . 62
A.3 Numeric Node Ids . 62
Annex B (normative) OPC UA Nodeset . 64
Annex C (normative) Type declarations for the OPC UA native Mapping . 65
Annex D (normative) WSDL for the XML Mapping . 66
D.1 XML Schema . 66
D.2 WDSL Port Types . 66
D.3 WSDL Bindings . 66
Annex E (normative) Security settings management . 67
E.1 Overview. 67
E.2 SecuredApplication . 68
E.3 CertificateIdentifier . 71
E.4 CertificateStoreIdentifier . 73
E.5 CertificateList . 73
E.6 CertificateValidationOptions . 73
Annex F (normative) Information Model XML Schema . 75
F.1 Overview. 75
F.2 UANodeSet . 75
F.3 UANode . 76
F.4 Reference . 76
F.5 UAType . 77

– 4 – IEC 62541-6:2015 © IEC 2015
F.6 UAInstance . 77
F.7 UAVariable . 77
F.8 UAMethod . 78
F.9 TranslationType . 78
F.10 UADataType . 79
F.11 DataTypeDefinition . 79
F.12 DataTypeField . 80
F.13 Variant . 80
F.14 Example (Informative) . 81

Figure 1 – The OPC UA Stack Overview . 13
Figure 2 – Encoding Integers in a binary stream . 16
Figure 3 – Encoding Floating Points in a binary stream . 17
Figure 4 – Encoding Strings in a binary stream . 17
Figure 5 – Encoding Guids in a binary stream . 18
Figure 6 – Encoding XmlElements in a binary stream . 19
Figure 7 – A String NodeId . 20
Figure 8 – A Two Byte NodeId . 20
Figure 9 – A Four Byte NodeId . 21
Figure 10 – Security handshake . 34
Figure 11 – Relevant XML Web Services specifications . 39
Figure 12 – The WS Secure Conversation handshake . 39
Figure 13 – OPC UA Secure Conversation MessageChunk . 43
Figure 14 – OPC UA TCP Message structure . 52
Figure 15 – Establishing a OPC UA TCP connection . 53
Figure 16 – Closing a OPC UA TCP connection . 53
Figure 17 – Recovering an OPC UA TCP connection . 55
Figure 18 – Scenarios for the HTTPS Transport . 58

Table 1 – Built-in Data Types . 14
Table 2 – Guid structure . 14
Table 3 – Supported Floating Point Types . 17
Table 4 – NodeId components . 19
Table 5 – NodeId DataEncoding values . 19
Table 6 – Standard NodeId Binary DataEncoding . 19
Table 7 – Two Byte NodeId Binary DataEncoding . 20
Table 8 – Four Byte NodeId Binary DataEncoding. 20
Table 9 – ExpandedNodeId Binary DataEncoding . 21
Table 10 – DiagnosticInfo Binary DataEncoding . 22
Table 11 – QualifiedName Binary DataEncoding . 22
Table 12 – LocalizedText Binary DataEncoding . 22
Table 13 – Extension Object Binary DataEncoding. 23
Table 14 – Variant Binary DataEncoding . 24
Table 15 – Data Value Binary DataEncoding . 25

Table 16 – Sample OPC UA Binary Encoded structure . 26
Table 17 – XML Data Type Mappings for Integers . 27
Table 18 – XML Data Type Mappings for Floating Points . 27
Table 19 – Components of NodeId . 29
Table 20 – Components of ExpandedNodeId . 30
Table 21 – Components of Enumeration . 33
Table 22 – SecurityPolicy . 35
Table 23 – ApplicationInstanceCertificate . 36
Table 24 – SignedSoftwareCertificate . 37
Table 25 – Kerberos UserTokenPolicy . 38
Table 26 – WS-* Namespace prefixes . 40
Table 27 – RST/SCT Mapping to an OpenSecureChannel Request . 41
Table 28 – RSTR/SCT Mapping to an OpenSecureChannel Response . 42
Table 29 – OPC UA Secure Conversation Message header . 44
Table 30 – Asymmetric algorithm Security header . 44
Table 31 – Symmetric algorithm Security header . 45
Table 32 – Sequence header . 45
Table 33 – OPC UA Secure Conversation Message footer . 46
Table 34 – OPC UA Secure Conversation Message abort body . 47
Table 35 – OPC UA Secure Conversation OpenSecureChannel Service . 47
Table 36 – Cryptography key generation parameters . 49
Table 37 – OPC UA TCP Message header . 50
Table 38 – OPC UA TCP Hello Message . 51
Table 39 – OPC UA TCP Acknowledge Message . 51
Table 40 – OPC UA TCP Error Message . 52
Table 41 – OPC UA TCP error codes . 54
Table 42 – WS-Addressing headers . 56
Table 43 – Well known addresses for Local Discovery Servers . 60
Table A.1 – Identifiers assigned to Attributes . 62
Table E.1 – SecuredApplication . 69
Table E.2 – CertificateIdentifier . 71
Table E.3 – Structured directory store . 72
Table E.4 – CertificateStoreIdentfier . 73
Table E.5 – CertificateList . 73
Table E.6 – CertificateValidationOptions . 74
Table F.1 – UANodeSet . 75
Table F.2 – UANode . 76
Table F.3 – Reference . 77
Table F.4 – UANodeSet Type Nodes. 77
Table F.5 – UANodeSet Instance Nodes . 77
Table F.6 – UAInstance . 77
Table F.7 – UAVariable . 78
Table F.8 – UAMethod . 78

– 6 – IEC 62541-6:2015 © IEC 2015
Table F.9 – TranslationType . 79
Table F.10 – UADataType . 79
Table F.11 – DataTypeDefinition . 80
Table F.12 – DataTypeField . 80

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPC UNIFIED ARCHITECTURE –
Part 6: Mappings
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62541-6 has been prepared by subcommittee 65E: Devices and
integration in enterprise systems, of IEC technical committee 65: Industrial-process
measurement, control and automation.
This second edition cancels and replaces the first edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Some applications need to operation in environments with no access to cryptography
libraries. To support this a new HTTPS transport has been defined in 7.3;
b) The padding byte is not long enough to handle asymmetric key sizes larger than 2048 bits.
Added an additional padding byte to 6.7.2 to handle this case.
c) Fixed errors in SOAP action URIs defined in 7.2.2;

– 8 – IEC 62541-6:2015 © IEC 2015
d) Needed a standard way to serialize nodes in an address space. Added the UANodeSet
schema defined in Annex F;
The text of this standard is based on the following documents:
CDV Report on voting
65E/377/CDV 65E/405/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 62541 series, published under the general title OPC Unified
Architecture, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
OPC UNIFIED ARCHITECTURE –
Part 6: Mappings
1 Scope
This part of IEC 62541 specifies the OPC Unified Architecture (OPC UA) mapping between
the security model described in IEC TR 62541-2, the abstract service definitions, described in
IEC 62541-4, the data structures defined in IEC 62541-5 and the physical network protocols
that can be used to implement the OPC UA specification.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC TR 62541-1, OPC Unified Architecture – Part 1: Overview and Concepts
IEC TR 62541-2, OPC Unified Architecture – Part 2: Security Model
IEC 62541-3, OPC Unified Architecture – Part 3: Address Space Model
IEC 62541-4, OPC Unified Architecture – Part 4: Services
IEC 62541-5, OPC Unified Architecture – Part 5: Information Model
IEC 62541-7, OPC Unified Architecture – Part 7: Profiles
XML Schema Part 1: XML Schema Part 1: Structures
http://www.w3.org/TR/xmlschema-1/
XML Schema Part 2: XML Schema Part 2: Datatypes
http://www.w3.org/TR/xmlschema-2/
SOAP Part 1: SOAP Version 1.2 Part 1: Messaging Framework
http://www.w3.org/TR/soap12-part1/
SOAP Part 2: SOAP Version 1.2 Part 2: Adjuncts
http://www.w3.org/TR/soap12-part2/
XML Encryption: XML Encryption Syntax and Processing
http://www.w3.org/TR/xmlenc-core/
XML Signature: XML-Signature Syntax and Processing
http://www.w3.org/TR/xmldsig-core/
WS Security: SOAP Message Security 1.1
http://www.oasis-open.org/committees/download.php/16790/wss-v1.1-spec-os-
SOAPMessageSecurity.pdf
– 10 – IEC 62541-6:2015 © IEC 2015
WS Addressing: Web Services Addressing (WS-Addressing)
http://www.w3.org/Submission/ws-addressing/
WS Trust: WS Trust 1.3
http://docs.oasis-open.org/ws-sx/ws-trust/v1.3/ws-trust.html
WS Secure Conversation: WS Secure Conversation 1.3
http://docs.oasis-open.org/ws-sx/ws-secureconversation/v1.3/ws-secureconversation.html
WS Security Policy: WS Security Policy 1.2
http://docs.oasis-open.org/ws-sx/ws-securitypolicy/200702/ws-securitypolicy-1.2-spec-
os.html
SSL/TLS: RFC 5246 – The TLS Protocol Version 1.2
http://tools.ietf.org/html/rfc5246.txt
X509: X.509 Public Key Certificate Infrastructure
http://www.itu.int/rec/T-REC-X.509-200003-I/e
WS-I Basic Profile 1.1: WS-I Basic Profile Version 1.1
http://www.ws-i.org/Profiles/BasicProfile-1.1.html
WS-I Basic Security Profile 1.1: WS-I Basic Security Profile Version 1.1
http://www.ws-i.org/Profiles/BasicSecurityProfile-1.1.html
HTTP: RFC 2616 – Hypertext Transfer Protocol – HTTP/1.1
http://www.ietf.org/rfc/rfc2616.txt
Base64: RFC 3548 – The Base16, Base32, and Base64 Data Encodings
http://www.ietf.org/rfc/rfc3548.txt
X690: ITU-T X.690 – Basic (BER), Canonical (CER) and Distinguished (DER) Encoding Rules
http://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf
IEEE-754: Standard for Binary Floating-Point Arithmetic
http://grouper.ieee.org/groups/754/
HMAC: HMAC – Keyed-Hashing for Message Authentication
http://www.ietf.org/rfc/rfc2104.txt
PKCS #1: PKCS #1 – RSA Cryptography Specifications Version 2.0
http://www.ietf.org/rfc/rfc2437.txt

FIPS 180-2: Secure Hash Standard (SHA)
http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf

FIPS 197: Advanced Encyption Standard (AES)
http://www.csrc.nist.gov/publications/fips/fips197/fips-197.pdf

UTF8: UTF-8, a transformation format of ISO 10646
http://tools.ietf.org/html/rfc3629
RFC 3280: RFC 3280 – X.509 Public Key Infrastructure Certificate and CRL Profile
http://www.ietf.org/rfc/rfc3280.txt
RFC 4514: RFC 4514 – LDAP: String Representation of Distinguished Names

http://www.ietf.org/rfc/rfc4514.txt
NTP: RFC 1305 – Network Time Protocol (Version 3)
http://www.ietf.org/rfc/rfc1305.txt
Kerberos: WS Security Kerberos Token Profile 1.1
http://docs.oasis-open.org/wss/v1.1/wss-v1.1-spec-os-KerberosTokenProfile.pdf
3 Terms, definitions, abbreviations and symbols
3.1 Terms and definitions
For the purposes of this document the terms and definitions given in IEC TR 62541-1,
IEC TR 62541-2 and IEC 62541-3 as well as the following apply.
3.1.1
DataEncoding
a way to serialize OPC UA Messages and data structures
3.1.2
Mapping
specifies how to implement an OPC UA feature with a specific technology
Note 1 to entry: For example, the OPC UA Binary Encoding is a Mapping that specifies how to serialize OPC UA
data structures as sequences of bytes.
3.1.3
Security Protocol
ensures the integrity and privacy of UA Messages that are exchanged between OPC UA
applications
3.1.4
Stack Profile
a combination of DataEncodings, SecurityProtocol and TransportProtocol Mappings
Note 1 to entry: OPC UA applications implement one or more StackProfiles and can only communicate with OPC
UA applications that support a StackProfile that they support.
3.1.5
Transport Protocol
a way to exchange serialized OPC UA Messages between OPC UA applications
3.2 Abbreviations and symbols
API Application Programming Interface
ASN.1 Abstract Syntax Notation #1 (used in X690)
BP WS-I Basic Profile Version
BSP WS-I Basic Security Profile
CSV Comma Separated Value (File Format)
HTTP Hypertext Transfer Protocol
HTTPS Secure Hypertext Transfer Protocol
IPSec Internet Protocol Security
RST Request Security Token
OID Object Identifier (used with ASN.1)
RSTR Request Security Token Response

– 12 – IEC 62541-6:2015 © IEC 2015
SCT Security Context Token
SHA1 Secure Hash Algorithm
SOAP Simple Object Access Protocol
SSL Secure Sockets Layer (Defined in SSL/TLS)
TCP Transmission Control Protocol
TLS Transport Layer Security (Defined in SSL/TLS)
UTF8 Unicode Transformation Format (8-bit) (Defined in UTF8)
UA Unified Architecture
UASC OPC UA Secure Conversation
WS-* XML Web Services Specifications
WSS WS Security
WS-SC WS Secure Conversation
XML Extensible Markup Language
4 Overview
Other parts of this series of standards are written to be independent of the technology used
for implementation. This approach means OPC UA is a flexible specification that will continue
to be applicable as technology evolves. On the other hand, this approach means that it is not
possible to build an OPC UA Application with the information contained in IEC TR 62541-1
through to IEC 62541-5 because important implementation details have been left out.
This standard defines Mappings between the abstract specifications and technologies that can
be used to implement them. The Mappings are organized into three groups: DataEncodings,
SecurityProtocols and TransportProtocols. Different Mappings are combined together to
create StackProfiles. All OPC UA Applications shall implement at least one StackProfile and
can only communicate with other OPC UA Applications that implement the same StackProfile.
This standard defines the DataEncodings in Clause 5, the SecurityProtocols in Clause 6 and
the TransportProtocols in 6.7.6. The StackProfiles are defined in IEC 62541-7.
All communication between OPC UA Applications is based on the exchange of Messages. The
parameters contained in the Messages are defined in IEC 62541-4; however, their format is
specified by the DataEncoding and TransportProtocol. For this reason, each Message defined
in IEC 62541-4 shall have a normative description which specifies exactly what shall be put
on the wire. The normative descriptions are defined in the appendices.
A Stack is a collection of software libraries that implement one or more StackProfiles. The
interface between an OPC UA Application and the Stack is a non-normative API which hides
the details of the Stack implementation. An API depends on a specific DevelopmentPlatform.
Note that the datatypes exposed in the API for a DevelopmentPlatform may not match the
datatypes defined by the specification because of limitations of the DevelopmentPlatform. For
example, Java does not support an unsigned integer which means that any Java API will need
to map unsigned integers onto a signed integer type.
Figure 1 illustrates the relationships between the different concepts defined in this standard.

Client
UA Application
Server
Development Platforms
.NET 3.0
API
ANSI C
JRE 5.0
Data Encodings
Serialization Layer
UA Binary
UA XML
Encoded Message
Security Protocols
WS Secure Conversation
Stack
Secure Channel Layer
UA Secure Conversation
Security Transforms
Signing
Secured Message
Encryption
Transport Protocols
Transport Layer UA TCP
SOAP/HTTP
W SDL and XML Schema
Wire Protocol
UA Binary Schema
Mappings
IEC
Figure 1 – The OPC UA Stack Overview
The layers described in this specification do not correspond to layers in the OSI 7 layer model
[X200]. Each OPC UA StackProfile should be treated as a single Layer 7 (Application)
protocol that is built on an existing Layer 5, 6 or 7 protocol such as TCP/IP, TLS or HTTP.The
SecureChannel layer is always present even if the SecurityMode is None. In this situation, no
security is applied but the SecurityProtocol implementation shall maintain a logical channel
with a unique identifier. Users and administrators are expected to understand that a
SecureChannel with SecurityMode set to None cannot be trusted unless the Application is
operating on a physically secure network or a low level protocol such as IPSec is being used.
5 Data encoding
5.1 General
5.1.1 Overview
This standard defines two data encodings: OPC UA Binary and OPC UA XML. It describes
how to construct Messages using each of these encodings.
5.1.2 Built-in Types
All OPC UA DataEncodings are based on rules that are defined for a standard set of built-in
types. These built-in types are then u
...