OPC Unified Architecture

OPC FOUNDATION HISTORY

The OPC Foundation’s forerunner – a task force composed of Fisher-Rosemount, Rockwell Software, Opto 22, Intellution, and Intuitive Technology – was able to develop a basic, workable, OPC specification after only a single year’s work. This standard was named “OLE for Process Control” as it was built on Microsoft COM/DCOM technology and acted like a device driver to enable PLC controllers to deliver live data, alarms and historical data. A simplified, stage-one solution was released in August 1996.

While each of the members worked for competing companies, they quickly established great relationships and focused on the task of developing a specification that was built on solid technology for interoperability. Sample code came first, followed by the specification. The OPC task force made sure that everything was feasible and exceeded the expectations of all the (competing) vendors since the goal was to develop technology that multiple vendors would quickly adopt in the interest of multi-vendor interoperability.

The today called “OPC classic” became defacto standard and formed the successful base of worldwide adopted interoperability standard and constantly increasing membership of OPC Foundation.

INDEPENDENCE

The OPC Foundation is a non-profit organization that is independent of individual manufacturers or special technologies. Members of the working groups come from member companies on a voluntary basis. The organization is financed entirely from membership fees and receives no government grants. The organization operates worldwide and has regional contacts on all continents. All members have identical voting rights, irrespective of their size.

MEMBER DISTRIBUTION

Although the head office is in Phoenix, Arizona, most members (above 50 %) are based in Europe. Around one third of the members are based in North America. All main manufacturers of automation technology are members of the OPC Foundation and already offer OPC technologies in their products.

THE NEW OPC GENERATION: OPC UA

In 2003 OPC Foundation started separating services from data and the OPC Unified Architecture (OPC UA) was created as a service-oriented architecture. It was designed to seamlessly deliver secure and reliable information exchange from sensors through to IT enterprise independent of operating systems, vendors and markets.

The challenge to adoption was a huge install base of existing OPC products based on OPC Classic which needed to migrate to the next generation OPC UA technology. As such, OPC UA had to take into account back-ward compatibility. After verification and implementation in 2006 and 2007 the OPC UA specification was finally released in 2008.

To better facilitate global adoption, the OPC UA was designed to become an IEC specification. Work on making the OPC UA standard compliant with IEC rules and templates commenced in 2010 and was completed in 2012. As a result, the OPC UA standard is now a full-fledged IEC standard known as IEC62541. In addition, the OPC UA standard has also been localized in different part of the world like China, Korea and Singapore.

OPC UA: At a Glance

SECURE, RELIABLE INTEROPERABILITY

OPC UA is the latest generation of OPC technology from the OPC Foundation. OPC UA rewrites the original OPC standard from the ground up and extends its relevance by addressing a broad range of modern communication requirements. As such, OPC UA delivers a secure, reliable transport of data and information from sensors and the shop floor to control systems, production planning systems, and beyond.

PLATFORM AND VENDOR-INDEPENDENT

OPC UA is an open standard without dependence on or binding to proprietary technologies or individual vendors. Hence, all OPC UA communications are 100% independent of the vendors who implement them, the programming languages used, and the platforms those products run on.

USES THE LATEST OPEN STANDARDS

OPC UA is based on a various types of standards and protocols carefully chosen based on their ability to meet the needs of specific OPC UA use cases.

For example:

  • For OPC UA Client-Server communications, OPC UA uses an optimized TCP based binary protocol for data exchange over the IANA registered port 4840.
  • For Cloud-based communications, OPC UA uses popular protocols like MQTT and AMQP.
  • For communication in the field OPC UA uses UDP and specialized protocols like TSN or 5G for deterministic communication.
  • Web Sockets may also be used to support browser-based OPC UA Clients. New protocol bindings like QUIC (UDP-based Internet protocol) can be integrated easily without breaking existing functionality.

ROBUST INFORMATION MODELING

Robust information modelling (IM) is built into the heart of the OPC UA standard. OPC UA defines base building blocks and consistent rules to build object-oriented models with them. In OPC UA it is possible to expose and discover information models in a consistent and universal manner between all OPC UA entities. OPC UA defines a few industry agnostic IMs that other organizations use as a common starting point to define their own OPC UA based IMs. OPC UA also defines the mechanisms needed to facilitate dynamic discovery and access to OPC UA IMs.

    This is crucial for 3rd party interoperability because different OPC UA implementations will natively implement different IMs.

    Key OPC UA functions include:

    • Browsing: A look-up mechanism used to locate object instances and their semantics
    • Read and write operations: used for current and historical data
    • Method execution
    • Notification for data and events

    CLIENT-SERVER

    OPC UA Client-Server communications are based on the service-oriented architecture (SOA) paradigm. Therefore, information model access is defined via services. Unlike classic Web services which describe their services using the xml-based Web Services Design Language (WSDL) which allows each service provider’s implementation to be different and hence not directly interoperable, OPC UA predefines generic standardized services to ensure all OPC UA implementations are compatible. A WSDL definition is not required in OPC UA, because the services are standardized. As a result, they are compatible and interoperable, without the caller needing to have any special knowledge about the structure or behaviour of a special service.

    PUBLISH-SUBSCRIBE (PUBSUB)

    PubSub provides an alternative mechanism for data and event notification. Unlike Client-Server communications, PubSub is optimized for many-to-many interactions where multiple clients may receive broadcasted notifications in a fire-and-forget fashion. With PubSub, OPC UA applications do not directly exchange requests and responses. Instead, Publishers send messages to Message Oriented Middleware without any knowledge about the Subscriber(s). Similarly, Subscribers express interest in specific types of data and process messages that contain this data without knowledge of the Publisher(s). PubSub and Client Server are based on the OPC UA Information Model. Publishers are typically OPC UA Servers and

    Subscribers are commonly OPC UA Clients. Local OPC UA Client-Server communications are used to setup PubSub components.

    STRONG SECURITY THAT IS SCALABLE

    OPC UA is based on accepted security concepts and standards that are also used for secure internet communications. Examples include SSL, TLS and AES. OPC UA offers protection against unauthorized access, sabotage, modification of process data, and careless operations. OPC UA security mechanisms include: user and application authentication, signing of messages, and data encryption. While users are free to choose which OPC UA security functions they want to use based on their infrastructure and context, vendors are obliged to implement all of them depending on the OPC UA profile they want to support. This ability to choose which security features are used makes OPC UA usable (scalable) in all types of environments (e.g. limited computing resources vs. large computer systems).

    ACCESSIBILITY AND RELIABILITY

    OPC UA defines a robust architecture with reliable communication mechanisms, configurable timeouts and automatic error detection that restores communications between OPC UA Clients and Servers without data loss. In addition, OPC UA redundancy functions for both client and server applications make OPC UA suitable for high-availability applications.

    SIMPLIFICATION BY UNIFICATION

    OPC UA defines an integrated address space and a unified information model that supports process data, alarms, historical data, and function calls (methods). Beyond OPC classic functionality, OPC UA also supports the description and use of complex procedures and systems in uniform object oriented components. Hence, OPC UA clients which only support basic rules can still process data from OPC UA Servers without any knowledge of the complex data structures residing in the OPC UA Server.

    GROWING AREAS OF ADOPTION

    The functional breadth of OPC UA makes it universal and applicable for use in an ever growing list of new markets and applications. From local plants to remote field stations behind firewalls – OPC UA is the right choice to standardize on. Other

    standards bodies increasingly use OPC UA as an interoperability platform for defining and implementing their own information models. Currently, the OPC Foundation cooperates with over 52 such groups from various industries, including: discrete and process automation, energy, engineering tool manufacturers, industrial kitchen equipment, and many more.

    About OPC Hub ASEAN/Singapore

    Beckhoff Singapore has been officially appointed as OPC Hub ASEAN and will coordinate activities on behalf of OPC Foundation within ASEAN. Mr. David Chia, Managing Director of Beckhoff Automation Pte. Ltd will act as the Head of the OPC Hub ASEAN with the key objectives to promote OPC UA Technology awareness and works towards support the interests of all OPC members in a neutral way.

    The first members of the OPC Hub are Ngee Ann Polytechnic and Singapore Polytechnic, who formed a collaboration to jointly organize, promote and showcase OPC-UA technology and offer training courses, test-bedding and “live“ demonstrations of the OPC-UA technology for the industries in Singapore. Both institutions will also hold regular seminars to educate and facilitate adoption and deployment of OPC UA products as well as development of vertical market application guidelines for specialized industries in the region.

    With OPC UA recently recognised as a Singapore Standard, we look forward to more involvement in the country’s move towards Industry 4.0.