OPC Unified Architecture (OPC UA) is a cross-platform, open-source, IEC62541 standard for data exchange from sensors to cloud applications developed by the OPC Foundation. Distinguishing characteristics are:
Standardized data models freely available for over 60 types of industrial equipment, published by the OPC Foundation via Companion Specifications Extensible security profiles, including authentication, authorization, encryption and checksums Extensible security key management, including X.509, token and password Support for both client-server and publish-subscribe communication patterns Communication protocol independent. Mappings to several communication protocols like TCP/IP, UDP/IP, WebSockets, AMQP and MQTT are specified Initially successful in standardized data exchange with industrial equipment (discrete manufacturing, process manufacturing, energy) and systems for data collection and control, but now also leveraged in building automation, weighing and kitchen equipment and cloud applications Open – open-source reference implementations freely available to OPC Foundation members, non members under GPL 2.0 license Cross-platform – not tied to one operating system or programming language Service-oriented architecture (SOA) The specification is freely available on the OPC Foundation website and is split into several parts to ease implementation, but only OPC UA stack vendors need to read them, end users simply leverage existing commercial and/or open-source stacks available in all popular programming languages
History Although developed by the same organization, OPC UA differs significantly from its predecessor, Open Platform Communications (OPC). The Foundation's goal for OPC UA was to provide a path forward from the original OPC communications model (namely the Microsoft Windows-only process exchange COM/DCOM) that would better meet the emerging needs of industrial automation.Mahnke, Wolfgang; Leitner, Stefan-Helmut https://library.e.abb.com/public/75d70c47268d78bfc125762d00481f78/56-61%203M903_ENG72dpi.pdf OPC Unified Architecture – The future standard for communication and information modeling in automation], 3/2009 ABB Review 3/2009, page 56-61
After more than three years of specification work and another year for a prototype implementation, the first version of the Unified Architecture was released in 2006.
The current version of the specification is on 1.04 (22 November 2017). The new version of OPC UA now has added publish/subscribe in addition to the client/server communications infrastructure.
Although the original binding to COM/DCOM helped OPC to distribute well, it had several drawbacks: Frequent configuration issues with DCOM; No configurable time-outs; Microsoft Windows only; Lower security; No control over DCOM (COM/DCOM is kind of a black box, developers have no access to sources and therefore have to deal with bugs or insufficient implementations).
These drawbacks along with a number of other considerations pushed the decision to develop a new and independent stack for OPC UA, which replaces COM/DCOM. The main characteristics of this communication stack were: Multi-platform implementation, including portable ANSI C, Java and .NET implementations; Scalability: from smart sensors and smart actuators to mainframes; Multi-threaded, as well as single-threaded/single-task operation—necessary for porting the stack to embedded devices; Security, based on new standards; Configurable time-outs for each service; Chunking of big datagrams.
This communication stack reflects the beginning of various innovations. The OPC UA architecture is a service-oriented architecture (SOA) and is based on different logical levels.
OPC Base Services are abstract method descriptions, which are protocol independent and provide the basis for OPC UA functionality. The transport layer puts these methods into a protocol, which means it serializes/deserializes the data and transmits it over the network. Two protocols are specified for this purpose. One is a binary TCP protocol, optimized for high performance and the second is Web service-oriented.
The OPC information model is a Mesh Network based on nodes. These nodes can include any kind of meta information, and are similar to the objects of object-oriented programming (OOP). A node can have attributes for read access such as DataAccess (DA), HistoricDataAccess (HDA), methods that can be called (Commands), and triggered events that can be transmitted (such as AlarmEvent (AE), DataAccess, and DataChange). Nodes hold process data as well as other types of metadata. The OPC namespace contains the type-model. The namespace is a URI that identifies the naming authority responsible for assigning the identifier element of the NodeId. Naming authorities include the local Server, the underlying system, standards bodies and consortia. It is expected that most Nodes will use the URI of the Server or of the underlying system. OPC UA defines a common infrastructure model to facilitate this information exchange, and specifies the following: The information model to represent structure, behaviour and semantics; The message model to interact between applications; The communication model to transfer the data between end-points; The conformance model to guarantee interoperability between systems.
Client software can verify what profiles a server supports. This is necessary to obtain information, if a server only supports DA functionality or additionally AE, HDA, etc. Additionally, information can be obtained about whether a server supports a given profile. New and important features of OPC UA are: Redundancy support Heartbeat for connections in both directions (to indicate whether the other end is "alive"). This means that both server and client recognize interrupts. Buffering of data and acknowledgements of transmitted data. Lost connections don't lead to lost data anymore. Lost datagrams can be refetched.
At the OPC UA DevCon in October 2006, in Munich the first prototypes were presented live. Various UA Servers have been shown on a Beckhoff programmable logic controller and an embedded test board from Euros. The Beckhoff PLC is based on Windows XP Embedded and the embedded controller is based on the real-time operating system Euros. The company Embedded Labs Ltd demonstrated an OPC UA Server based on their own C++ UA Stack executing on a single chip ARM microcontroller with 64kB RAM. In October 2012 the German Fraunhofer-Application Center IOSB-INA and the Institute for industrial Information Technologies (inIT) showed that an OPC UA server is scalable down to 15 kB RAM and 10 kB ROM and therefore usable at chip level.
The current version of the specification is 1.05.06, and was released on 22 October, 2025.
Specifications The OPC UA specification is a multi-part specification and consists of the following parts: Concepts Security Model Address Space Model Services Information Model Mappings Profiles Data Access Alarms and Conditions Programs Historical Access Discovery and Global Services Aggregates PubSub Safety State Machines Alias Names Role-Based Security Dictionary Reference File Transfer Device Onboarding Base Network Model Common Reference Types Scheduler
Additionally, part 100 Devices, and part 200 Industrial Automation are also available. These build on the core set of specifications, and adds new common definitions that then are used in different companion specifications. E.g. both OPC UA for Analyser Devices and OPC UA for Machinery builds directly on part 100.
In contrast to the COM-based specifications, the UA specifications are not pure application specifications. They describe typical UA internal mechanisms, which get handled through the communication stack and are normally only of interest for those that port a stack to a specific target or those that want to implement their own UA stack.
The OPC UA application developers code against the OPC UA API and therefore mainly use API documentation. Nevertheless, part 3, 4, and 5 may be of interest for application developers.Massaro, Simone What is OPC UA and how does it affect your world?, 5/15/2008 planetengineering.com
OSI model OPC UA is a OSI model Layer 7: Application layer
With in the Application layer, OPC UA have 4 sub layers: +OPC UA Stack OverviewLayerDescriptionOPC UA standardUA ApplicationClient ServerSerialization layer Data EncodingOPC 10000-6 UA Part 6: Mappings: DataEncodingSecure channel layerSecure ProtocolsOPC 10000-6 UA Part 6: Mappings: SecurityProtocolTransport layerTransport ProtocolsOPC 10000-6 UA Part 6: Mappings: TransportProtocols OPC 10000-14: UA Part 14: PubSub: Transport Protocol Mappings
Transport Protocols OPC UA is a versatile industrial communication protocol that is designed to be transport-agnostic, and operate over several transport mechanisms, each corresponding to different layers of the OSI model. It can use, TCP, UDP or Ethernet directly, or it can also be encapsulated within higher-level application protocols such as HTTPS, WebSockets, AMQP, and MQTT.
OPC-UA support: +OPC UA Transport protocolsProtocol nameOSI LayerOPC UA standardinfoOPC UA UDP4OPC 10000-14: UA Part 14: PubSub, OPC UA UDPSupport Multicast, Broadcast, Unicast, DTLSOPC UA Ethernet2OPC 10000-14: UA Part 14: PubSub: OPC UA EthernetEtherType for UADP is 0xB62CAMQP7OPC 10000-14: UA Part 14: PubSub: AMQPMQTT7OPC 10000-14: UA Part 14: PubSub: MQTTHTTPS7OPC 10000-6 UA Part 6: Mappings: OPC UA HTTPSWebSockets7OPC 10000-6 UA Part 6: Mappings: WebsocketsOPC UA TCP4OPC 10000-6 UA Part 6: Mappings: OPC UA TCP
UA communication stack The architecture of a UA application, independent of whether it is the server or client part, is structured into levels.
Some parts equalize to the former COM Proxy/Stubs and get provided by the OPC Foundation. The portability level is new; it simplifies porting the UA ANSI C stack to other target platforms. A port layer for Windows and Linux is also provided by the OPC Foundation.
UA security UA Security consists of authentication and authorization, encryption and data integrity via signatures. For Web Services the WS-SecureConversation gets used and is therefore compatible with .NET and other SO–AP implementations. For the binary variant, the algorithms of WS-SecureConversation have been followed and also converted to a binary equivalent. This is named as UA Secure Conversation.
There is also a mixed version where the code is binary, but the transport layer is SOAP. This is a compromise between efficient binary coding and firewall-friendly transmission. Binary coding always requires UA Secure Conversation. The authentication uses X.509 certificates exclusively. It relies on the application developer to choose which certificate store the UA application gets bound to. For instance, it is possible to use the public key infrastructure (PKI) of an Active Directory.
Built-in data types The OPC UA standard defines 25 built-in data types: +