OPC unified architecture - Part 1: Overview and concepts

This part of IEC 62541 presents the concepts and overview of the OPC Unified Architecture (OPC UA). Reading this document is helpful to understand the remaining parts of this multi-part document set. Each of the other parts of IEC 62451 is briefly explained along with a suggested reading order.

OPC Unified Architecture - Teil 1: Übersicht und Konzepte

Architecture unifiée OPC - Partie 1: Vue d'ensemble et concepts

IEC TR 62541-1:2020 est disponible sous forme de IEC TR 62541-1:2020 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.

Enotna arhitektura OPC - 1. del: Pregled in koncepti

General Information

Status
Published
Publication Date
07-Sep-2021
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
27-Jul-2021
Due Date
01-Oct-2021
Completion Date
08-Sep-2021

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SLOVENSKI STANDARD
SIST-TP CLC IEC/TR 62541-1:2021
01-oktober-2021
Nadomešča:
SIST-TP CLC/TR 62541-1:2010
Enotna arhitektura OPC - 1. del: Pregled in koncepti
OPC unified architecture - Part 1: Overview and concepts
OPC Unified Architecture - Teil 1: Übersicht und Konzepte
Architecture unifiée OPC - Partie 1: Vue d'ensemble et concepts
Ta slovenski standard je istoveten z: CLC IEC/TR 62541-1:2021
ICS:
25.040.40 Merjenje in krmiljenje Industrial process
industrijskih postopkov measurement and control
35.100.01 Medsebojno povezovanje Open systems
odprtih sistemov na splošno interconnection in general
SIST-TP CLC IEC/TR 62541-1:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CLC IEC/TR 62541-1:2021
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SIST-TP CLC IEC/TR 62541-1:2021
TECHNICAL REPORT CLC IEC/TR 62541-1
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
July 2021
ICS 25.040.40; 35.100.01 Supersedes CLC/TR 62541-1:2010
English Version
OPC unified architecture - Part 1: Overview and concepts
(IEC/TR 62541-1:2020)

Architecture unifiée OPC - Partie 1: Vue d'ensemble et OPC Unified Architecture - Teil 1: Übersicht und Konzepte

concepts (IEC/TR 62541-1:2020)
(IEC/TR 62541-1:2020)
This Technical Report was approved by CENELEC on 2021-07-05.

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,

Turkey 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

© 2021 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. CLC IEC/TR 62541-1:2021 E
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SIST-TP CLC IEC/TR 62541-1:2021
CLC IEC/TR 62541-1:2021 (E)
European foreword

This document (CLC IEC/TR 62541-1:2021) consists of the text of IEC/TR 62541-1:2020, prepared by

SC 65E "Devices and integration in enterprise systems" of IEC/TC 65 "Industrial-process

measurement, control and automation".
This document supersedes CLC/TR 62541-1:2010.

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.

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 Technical Report IEC/TR 62541-1:2020 was approved by CENELEC as a

European Technical Report without any modification.
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SIST-TP CLC IEC/TR 62541-1:2021
CLC IEC/TR 62541-1:2021 (E)
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.cenelec.eu.
Publication Year Title EN/HD Year
IEC/TR 62541-2 - OPC unified architecture – Part 2: CLC/TR 62541-2 -
Security Mode
IEC 62541-3 - OPC Unified Architecture - Part 3: EN IEC 62541-3 -
Address Space Model
IEC 62541-4 - OPC Unified Architecture - Part 4: EN IEC 62541-4 -
Services
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 62541-10 - OPC Unified Architecture - Part 10: EN IEC 62541-10 -
Programs
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 62541-14 - OPC unified architecture - Part 14: EN IEC 62541-14 -
PubSub
ITU X.509 - Information technology – Open Systems
Interconnection – The Directory: Public-
key and attribute certificate
frameworkshttps://www.itu.int/rec/T-REC-
X.509
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SIST-TP CLC IEC/TR 62541-1:2021
IEC TR 62541-1
Edition 3.0 2020-11
TECHNICAL
REPORT
colour
inside
OPC unified architecture –
Part 1: Overview and concepts
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 25.040.40; 35.100.01 ISBN 978-2-8322-9076-7

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
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SIST-TP CLC IEC/TR 62541-1:2021
– 2 – IEC TR 62541-1:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms, definitions, and abbreviated terms ....................................................................... 7

3.1 Terms and definitions .............................................................................................. 7

3.2 Abbreviated terms ................................................................................................. 11

4 Structure of the OPC UA series ..................................................................................... 12

4.1 Specification organization ..................................................................................... 12

4.2 Core specification parts ........................................................................................ 12

4.3 Access Type specification parts ............................................................................ 13

4.4 Utility specification parts ....................................................................................... 13

5 Overview ....................................................................................................................... 14

5.1 UA scope .............................................................................................................. 14

5.2 General ................................................................................................................. 14

5.3 Design goals ......................................................................................................... 14

5.4 Integrated models and services............................................................................. 16

5.4.1 Security model ............................................................................................... 16

5.4.2 Integrated AddressSpace model .................................................................... 17

5.4.3 Integrated object model ................................................................................. 18

5.4.4 Integrated services ........................................................................................ 18

5.5 Sessions ............................................................................................................... 18

6 Systems concepts ......................................................................................................... 19

6.1 Client Server Overview ......................................................................................... 19

6.2 OPC UA Clients .................................................................................................... 19

6.3 OPC UA Servers ................................................................................................... 20

6.3.1 General ......................................................................................................... 20

6.3.2 Real objects .................................................................................................. 20

6.3.3 Server application .......................................................................................... 20

6.3.4 OPC UA AddressSpace ................................................................................. 21

6.3.5 Subscription entities ...................................................................................... 21

6.3.6 OPC UA Service Interface ............................................................................. 21

6.3.7 Server to Server interactions ......................................................................... 22

6.4 Redundancy .......................................................................................................... 23

6.5 Publish-Subscribe ................................................................................................. 23

6.6 Synergy of models ................................................................................................ 24

7 Service Sets .................................................................................................................. 25

7.1 General ................................................................................................................. 25

7.2 Discovery Service Set ........................................................................................... 25

7.3 SecureChannel Service Set .................................................................................. 25

7.4 Session Service Set .............................................................................................. 26

7.5 NodeManagement Service Set .............................................................................. 26

7.6 View Service Set ................................................................................................... 26

7.7 Query Service Set ................................................................................................. 26

7.8 Attribute Service Set ............................................................................................. 27

7.9 Method Service Set ............................................................................................... 27

7.10 MonitoredItem Service Set .................................................................................... 27

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7.11 Subscription Service Set ....................................................................................... 28

Figure 1 – OPC UA specification organization ....................................................................... 12

Figure 2 – OPC UA target applications .................................................................................. 15

Figure 3 – OPC UA System architecture ............................................................................... 19

Figure 4 – OPC UA Client architecture .................................................................................. 19

Figure 5 – OPC UA Server architecture ................................................................................ 20

Figure 6 – Peer-to-peer interactions between Servers ........................................................... 22

Figure 7 – Chained Server example ...................................................................................... 23

Figure 8 – Integrated Client Server and PubSub models ....................................................... 24

Figure 9 – SecureChannel and Session Services .................................................................. 26

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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPC UNIFIED ARCHITECTURE –
Part 1: Overview and concepts
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.

The main task of IEC technical committees is to prepare International Standards. However, a

technical committee may propose the publication of a technical report when it has collected

data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC TR 62541-1, which is a Technical Report, has been prepared by subcommittee 65E:

Devices and integration in enterprise systems, of IEC technical committee 65: Industrial-

process measurement, control and automation.

This third edition cancels and replaces the second edition of IEC TR 62541-1, published in

2016. This edition constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

a) added Subclauses 6.5 and 6.6 and other text throughout to include PubSub introduction;

b) added new transports and encodings to existing overview sections;
c) removed WS-SecureConversation example since this mapping has been deprecated;
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IEC TR 62541-1:2020 © IEC 2020 – 5 –
d) improved the definition of Certificate.
The text of this Technical Report is based on the following documents:
Enquiry draft Report on voting
65E/678/DTR 65E/702/RVDTR

Full information on the voting for the approval of this technical report 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.

Throughout this document and the referenced other Parts of the series, certain document

conventions are used:

Italics are used to denote a defined term or definition that appears in the “Terms and definition”

clause in one of the parts of the series.

Italics are also used to denote the name of a service input or output parameter or the name of

a structure or element of a structure that are usually defined in tables.

The italicized terms and names are also often written in camel-case (the practice of writing

compound words or phrases in which the elements are joined without spaces, with each

element's initial letter capitalized within the compound). For example, the defined term is

AddressSpace instead of Address Space. This makes it easier to understand that there is a

single definition for AddressSpace, not separate definitions for Address and Space.

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.

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– 6 – IEC TR 62541-1:2020 © IEC 2020
OPC UNIFIED ARCHITECTURE –
Part 1: Overview and concepts
1 Scope

This part of IEC 62541 presents the concepts and overview of the OPC Unified Architecture

(OPC UA). Reading this document is helpful to understand the remaining parts of this multi-part

document set. Each of the other parts of IEC 62451 is briefly explained along with a suggested

reading order.
2 Normative references

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.
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 62541-6, OPC unified architecture – Part 6: Mappings
IEC 62541-7, OPC unified architecture – Part 7: Profiles
IEC 62541-8, OPC unified architecture – Part 8: Data access
IEC 62541-9, OPC unified architecture – Part 9: Alarms and Conditions
IEC 62541-10, OPC unified architecture – Part 10: Programs
IEC 62541-11, OPC unified architecture – Part 11: Historical Access
IEC 62541-12, OPC unified architecture – Part 12: Discovery and global services
IEC 62541-13, OPC Unified Architecture – Part 13: Aggregates
IEC 62541-14, OPC unified architecture – Part 14: PubSub

ITU X.509, Information technology – Open Systems Interconnection – The Directory: Public-key

and attribute certificate frameworks
https://www.itu.int/rec/T-REC-X.509
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IEC TR 62541-1:2020 © IEC 2020 – 7 –
3 Terms, definitions, and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
AddressSpace
collection of information that a Server makes visible to its Clients

Note 1 to entry: See IEC 62541-3 for a description of the contents and structure of the Server AddressSpace.

3.1.2
Aggregate
function that calculates derived values from Raw data

Note 1 to entry: Raw data may be from a historian or buffered real time data. Common Aggregates include averages

over a given time range, minimum over a time range and maximum over a time range.

3.1.3
Alarm

type of Event associated with a state condition that typically requires acknowledgement

Note 1 to entry: See IEC 62541-9 for a description of Alarms.
3.1.4
Attribute
primitive characteristic of a Node

Note 1 to entry: All Attributes are defined by OPC UA, and may not be defined by Clients or Servers. Attributes are

the only elements in the AddressSpace permitted to have data values.
3.1.5
Broker

intermediary program module that routes NetworkMessages from Publishers to Subscribers

Note 1 to entry: Brokers are building blocks of Message Oriented Middleware.
3.1.6
Certificate

digitally signed data structure that contains a public key and the identity of a Client or Server

3.1.7
Client

software application that sends Messages to OPC UA Servers conforming to the Services

specified in this set of specifications
3.1.8
Condition
generic term that is an extension to an Event

Note 1 to entry: A Condition represents the conditions of a system or one of its components and always exists in

some state.
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3.1.9
Communication Stack

layered set of software modules between the application and the hardware that provides various

functions to encode, encrypt and format a Message for sending, and to decode, decrypt and

unpack a Message that was received
3.1.10
DataSet
list of named data values

Note 1 to entry: A DataSet typically consists of Event fields or Variable values.

3.1.11
DataSetMessage
payload of a NetworkMessage created from a DataSet

Note 1 to entry: The DataSetMessage is an immutable payload of the NetworkMessage handed off to the Message

Oriented Middleware (transport layer) for delivery by the Publisher. The Subscriber receives the DataSetMessage as

the payload of a NetworkMessage from the Publisher with additional headers that may be supplied by the Message

Oriented Middleware along the way.
3.1.12
Discovery

process by which Client obtains information about Servers, including endpoint and security

information
3.1.13
Event

generic term used to describe an occurrence of some significance within a system or system

component
3.1.14
EventNotifier

special Attribute of a Node that signifies that a Client may subscribe to that particular Node to

receive Notifications of Event occurrences
3.1.15
Information Model

organizational framework that defines, characterizes and relates information resources of a

given system or set of systems

Note 1 to entry: The core AddressSpace model supports the representation of Information Models in the

AddressSpace. See IEC 62541-5 for a description of the base OPC UA Information Model.

3.1.16
Message

data unit conveyed between Client and Server that represents a specific Service request or

response
3.1.17
Message Oriented Middleware

infrastructure supporting sending and receiving NetworkMessages between distributed systems

Note 1 to entry: An OPC UA Application may support different types of Message Oriented Middleware

infrastructures and protocols like AMQP, MQTT, or UDP with IP multicast. Other types like DDS or XMPP can also

be integrated into the OPC UA PubSub model.
3.1.18
Method
callable software function that is a component of an Object
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3.1.19
MonitoredItem

Client-defined entity in the Server used to monitor Attributes or EventNotifiers for new values

or Event occurrences and that generates Notifications for them
3.1.20
NetworkMessage

DataSetMessages and header to facilitate delivery, routing, security and filtering

Note 1 to entry: The Publisher hands off the NetworkMessage to the Message Oriented Middleware (transport layer)

to deliver DataSetMessages to the Subscribers.

Note 2 to entry: The term message is used with various connotations in the messaging world. The Publisher might

like to think of the message as an immutable payload handed off to the Message Oriented Middleware for delivery.

The Subscriber often thinks of the message as not only that immutable payload from the sender, but also various

annotations supplied by the Message Oriented Middleware along the way. To avoid confusion, the term

DataSetMessage is used to mean the message as supplied by the Publisher for a DataSet and the term

NetworkMessage is used to mean the DataSetMessage plus sections for annotation at the head and tail of the

DataSetMessage.
3.1.21
Node
fundamental component of an AddressSpace
3.1.22
NodeClass
class of a Node in an AddressSpace

Note 1 to entry: NodeClasses define the metadata for the components of the OPC UA object model. They also

define constructs, such as Views, that are used to organize the AddressSpace.
3.1.23
Notification

generic term for data that announces the detection of an Event or of a changed Attribute value;

Notifications are sent in NotificationMessages.
3.1.24
NotificationMessage
Message published from a Subscription that contains one or more Notifications
3.1.25
Object
Object Instance
Node that represents a physical or abstract element of a system

Note 1 to entry: Objects are modelled using the OPC UA Object Model. Systems, subsystems and devices are

examples of Objects. An Object may be defined as an instance of an ObjectType.
3.1.26
ObjectType
Node that represents the type definition for an Object
3.1.27
OPC UA Application

Client, which calls OPC UA Services, or a Server, which performs those Services, or an OPC

UA Publisher or an OPC UA Subscriber
3.1.28
Publisher
entity sending NetworkMessages to a Message Oriented Middleware
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Note 1 to entry: A Publisher can be a native OPC UA Application or an application that only has knowledge about

the Message Oriented Middleware and the rules for encoding the NetworkMessages and DataSetMessages.

3.1.29
PubSub
OPC UA variant of the publish subscribe messaging pattern
3.1.30
Profile
specific set of capabilities to which a Server may claim conformance
Note 1 to entry: Each Server may claim conformance to more than one Profile.
Note 2 to entry: The set of capabilities are defined in IEC 62541-7.
3.1.31
Program

executable Object that, when invoked, immediately returns a response to indicate that execution

has started, and then returns intermediate and final results through Subscriptions identified by

the Client during invocation
3.1.32
Reference
explicit relationship (a named pointer) from one Node to another

Note 1 to entry: The Node that contains the Reference is the source Node, and the referenced Node is the target

Node. All References are defined by ReferenceTypes.
3.1.33
ReferenceType
Node that represents the type definition of a Reference

Note 1 to entry: The ReferenceType specifies the semantics of a Reference. The name of a ReferenceType

identifies how source Nodes are related to target Nodes and generally reflects an operation between the two, such

as “A contains B”.
3.1.34
Server
software application that implements and exposes the Services spe
...

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