Rockwell Automation has now joined the group of companies that sees TSN plus OPC UA as 'the' end-to-end communication solution across the entire automation pyramid. Siemens also wants to use TSN across the entire pyramid, but has so far only used OPC UA down to controller level. Is the US company's move perhaps now changing your attitude?

Rainer Brehm: As far as Siemens is concerned, we are trying to act from a market perspective. And we can see from our first implementation that there is still a lot to be clarified and corresponding activities to be implemented in terms of controller-controller communication and the companion specs for the interfaces alone.

Thomas Hahn: When we finally manage to communicate across machines in a standardized way - and also manage to standardize the connections to the MES and SCADA world - then we can think about further steps. We at Siemens and the OPC Foundation want to concentrate on these tasks for the time being - right down to the controllers.

Both Rockwell Automation and Siemens are founding members of the OPC Foundation and both have a very important say in the direction of the OPC Foundation. Will Rockwell's decision change the direction of the OPC Foundation? In other words, will the Foundation now also promote OPC UA at field level?

Thomas Hahn, Chief Expert Software at Siemens, Vice President of the OPC Foundation and Chairman of LNI 4.0: "The OPC Foundation has an enormous range of tasks ahead of it - we are working flat out on how we can cope with this."

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Brehm : And even the layer 2 process is not to be sneezed at, as our current efforts within the IEC/IEEE 60802 Joint Working Group show. Standardization efforts are currently underway there with the global community, where we are trying to take the right steps from an automation market perspective.

However, if the shapers - with a tailwind from Rockwell Automation - are now pushing the topic of OPC UA plus TSN at field level and thus competing with the established fieldbuses ...

Brehm:... then these activities should be organized under the umbrella of the OPC Foundation! We agree with the shapers on this. Ultimately, the OPC Foundation should be the place where discussions are held for everything relating to the OPC plus TSN bundle. The companies' experts have been sitting there for a long time; it is a recognized open community. The future of OPC UA plus TSN will only be successful under a common OPC umbrella.

What about further tasks, such as the necessary device certifications? Can the OPC Foundation even cope with this organizationally? Should the fieldbus organizations perhaps be involved in this?

Hahn: Internally, the OPC Foundation has all the mechanisms in place to quickly set up further working groups, if these make sense. Nothing stands in the way of scaling. And then a comment on TSN: The OPC UA over TSN group with more than 80 participants is already meeting under the umbrella of the OPC Foundation - there is room there to drive forward the other tasks together with other partners ...

Brehm: ... important questions still need to be clarified: To what extent would companies come together in an OPC Foundation to define certain fieldbus services in a task force? And: Do you want to use existing infrastructures or build new ones?

Is the life cycle of fieldbus organizations now slowly coming to an end?

Hahn: We don't think so. The PNO, the ODVA and others have concluded cooperation agreements with the OPC Foundation for a reason ...

Brehm:...and we don't see the end of Profinet either. We see many applications where Profinet fits well and many cases where Profinet on TSN fits even better! We are now taking Profinet to the next level, making it future-proof with TSN and ensuring a prudent migration to TSN-based standards. In addition, there will of course be use cases where OPC UA plus TSN is a better fit - and we can imagine offering such a solution.

The PNO and the OPC Foundation have set up a joint working group on safety using Profisafe and operating it via OPC UA with or without TSN. Can this solution be implemented as the 'only' quasi-standard safety solution, especially as important features such as the pub/sub mechanism are missing from Profisafe?

Hahn: The signal came from the PNO: we would like to make Profisafe available and the OPC said: ok! In January, we convened a working group to examine Profisafe in the context of OPC. This group is already running successfully!

Brehm: Profisafe is probably the most established safety profile for device communication worldwide. If you are aiming for convergence from the user's perspective within the framework of OPC UA - both at controller-controller level and at field level - then it would make sense to use Profisafe. We are actively working on this concrete step towards greater consistency. As client/server is available today, we are of course tackling this first, pub/sub via TSN will follow shortly, the necessity is undisputed.

How soon can products for TSN plus OPC UA generally be expected?

Brehm: The question is, when will TSN have the necessary mass in the market? The answer depends heavily on the issue of standardization. But to achieve breadth, you also need an ecosystem - in other words, many manufacturers that offer TSN. You need valve terminals, you need sensors and actuators. And you need the corresponding chips and the corresponding protocols. A gut feeling would be: If it happens extremely quickly - three years, but more likely four to five years. Ultimately, it will be the added value of TSN and OPC UA for the customer that will determine the speed.