The first OPC UA specifications with the core functionality were released in 2008 and have therefore been available for more than a decade. The sustainability of the architecture is demonstrated by the fact that no incompatible changes or even a 'version 2' have been necessary to cover new requirements. Up to version 1.03 from 2015, smaller features were added or completed and, above all, the quality of the specification and the certification tests based on it were improved. The first major enhancement was the addition of a publish/subscribe communication model (PubSub) to the client/server communication model and the associated protocols in version 1.04, which reached its release status in 2018.

The major release cycles for OPC UA specifications are typically three years. However, due to the large number of companion specifications based on OPC UA, more and more features are being identified that are generally valid and should therefore be included in the OPC UA specification. In order to ensure faster availability, the OPC UA working group has started to publish smaller or completed features as amendments to the released specification.

OPC UA is essentially stable, but will probably never achieve the status of 'fully specified', as the construction kit for industrial interoperability is always being expanded with further solution modules based on real requirements.

The determinism requirement

As an extension to OPC UA version 1.04, three further amendments have already been released. More are in the works.

© OPC Foundation

Most of the requirements for OPC UA can be solved at the information model level. This means that no changes need to be made to the communication models or protocols. The requirement for real-time capable communication in OPC UA is an exception here. The first aspect to be added was the OPC UA PubSub communication model. It has been released with version 1.04.
At the same time, a sub-working group of the OPC UA working group was set up to investigate the use of Time Sensitive Networking (TSN) as an extension to standard Ethernet for OPC UA. The necessary TSN parameters for the PubSub model are currently being defined. These are also to be published as an amendment to OPC UA 1.04.

The focus here was initially on controller-to-controller communication, also with the requirement to be able to provide a black channel for a safety protocol. There has also been a 'PROFIsafe over OPC UA' working group for such safety solutions since the beginning of 2018. This group is expected to deliver initial results in 2019.

Field level communication

Over the past two years, the use of OPC UA for communication right down to the field devices has increasingly become the subject of discussion. In November 2018, the OPC Foundation therefore launched the Field Level Communication (FLC) initiative to bundle all global activities with the extended requirements. The vision of the initiative is to strive for an open, uniform, secure and standards-based IIoT communication solution between sensors, actuators, controllers and a cloud that meets all the requirements of industrial automation. This also explicitly addresses deterministic communication and functional safety as an optional feature.

The 23 initial supporting companies of the FLC-SC - the group is open to further members.

© OPC Foundation

Following the public appeal, 23 large, globally active member companies of the OPC Foundation pledged their support in just four weeks. In the FLC-SC (Steering Committee), they not only want to jointly coordinate the requirements and roadmaps, but also provide the necessary budgets to finance the FLC activities in addition to the existing membership fees. The companies in the group come from all regions of the world and cover a large part of the global market for industrial automation.

Following the first public announcement at SPS IPC Drives 2018, the group has already started work at full speed: The kick-off meeting took place in Frankfurt on December 17 and 18, 2018; 40 representatives of the 23 FLC-SC companies were present to create the necessary regulations and get the technical working groups off the ground. All OPC Foundation member companies (except 'only' logo members) can participate in the technical working groups as part of their normal membership. Following the public call, 160 employees have already registered for the new FLC working group. The kick-off of the technical working group in Munich from January 8 to 10, 2019 was attended by 90 participants from 36 companies.

The FLC working group aims to solve all automation requirements for communication with field devices - for external communication, the objectives and the status of development are coordinated between the FLC marketing group and the OPC Foundation. TSN is just one variant as a deterministic transmission channel alongside conventional Ethernet and, in future, 5G. This is why the name of the initiative is not 'OPC UA over TSN', as this would only cover one aspect of the comprehensive approach. The overarching standard is 'OPC UA' and this also includes the possibility of using TSN as an option if deterministic transmission is required.

A working group already existed for the safety aspect; this will now be integrated into the FLC working group. The topic of motion is a new addition. It is important to note that the range of tasks should not end with the definition of drive profiles. The group agrees that duplicate specifications for TSN must be avoided at all costs. The OPC Foundation has therefore concluded cooperation agreements with IEC and IEEE in order to coordinate the activities for IEEE 802.1 and IEC 60802 with FLC and make them usable in FLC. In future, there may only be a single TSN cable over which various real-time services can be handled simultaneously - including OPC UA. The Foundation did not set out with the aim of defining a new fieldbus, but rather to integrate existing approaches into OPC UA. The most important aspect is to have the information models available end-to-end from the sensor to the cloud with integrated security. And so, as always, the market will ultimately decide according to the criteria: Cost, consistency, performance, manageability of complexity, diagnostic options and availability.

Upcoming challenge

OPC UA has become a kind of 'movement' that hardly any company can refuse to join: The huge investment alone is evident from the 50 or so industrial groups currently working on companion specifications. The aim is to plug and play standardized information, which is then exchanged using OPC UA mechanisms - optionally also deterministically at field level, even if not deterministically up to the public cloud. There is still a long way to go, but it is extremely exciting: this goal can only be achieved under the umbrella of the OPC Foundation as the 'United Nations of Automation'. The will and spirit to find a common solution was clearly noticeable at the previous meetings.

The real challenge for the OPC Foundation, however, lies in the harmonization of information models in order to avoid 'conflicts of information models'. The OPC Foundation has recognized this and put it on the public roadmap: https://opcfoundation.org/about/opc-technologies/opc-ua/opcua-roadmap/

Authors: Matthias Damm is CEO at Ascolab and Stefan Hoppe is President of the OPC Foundation.