July 26, 2019
John Kowal, director of business development at B&R Industrial Automation, provided this FAQ on OPC UA over TSN. B&R is a 'committed contributor' to the 'OPC UA including TSN down to the field level' initiative.

Q: What exactly is the performance of OPC UA over TSN?

A: The technology is capable of addressing 10,000 network nodes, scalable from 10 Mb to 10 Gb. B&R conducted a test achieving cycle times below 50 µs with a jitter of ±100 ns in a network of 200 remote I/O modules. This level of performance makes proprietary fieldbus networks operating under an OPC UA over TSN network unnecessary. OPC UA over TSN allows high-performance motion traffic and bandwidth-intense IT traffic on one cable without interfering with each other.

Download a detailed white paper on the topic of OPC UA over TSN implementation.

Q: Will OPC UA over TSN make it easier to integrate factory and machine networks with our IT requirements?

A: OPC UA was designed to communicate with IT systems. OPC UA over TSN will enable you to use converged OT networks with IT networks, using security mechanisms familiar to IT departments today. The flavors of Ethernet used in fieldbus communications are typically not standard IEEE 802.1 platforms, are therefore not familiar to IT personnel, and do not work with the IT department’s configuration tools.

Q: What are the main differences between OPC UA over TSN and running the various existing fieldbus protocols over TSN?

A: The legacy fieldbus protocols would share a common TSN network, but devices are not interoperable; only devices standardizing on OPC UA are. Also, they do not provide semantics, whereas OPC UA does. OPC UA has built-in security. OPC UA is widely supported and new developments continue to be supported. It is a recognized international standard for communication from sensor to cloud. Interoperability is very important. Without system interoperability, you are locked into one vendor, limiting your options to one automation solution, with no ability to communicate or synchronize with other systems. You are limited to the level of innovation offered by your chosen vendor. As a practical operational capability, users have long sought interoperability between machines from different suppliers with different control platforms installed in their plants in order to perform tasks such as condition monitoring, line balancing, predictive maintenance, machine optimization and plug-and-produce startups.

At the engineering phase for the machine builder, and commissioning and maintenance for the end user, using different communications protocols might require a higher level of resources—for example, if motion is not supported, a separate motion network could be required.

Q: If my plant is standardized on one of the existing fieldbus protocols, is there any advantage to switching to OPC UA over TSN?

A: The main advantages are semantics, security and performance. Performance aspects include high bandwidth and guaranteed real-time communication.

A machine builder would need to support every major fieldbus over TSN, whereas the extension of OPC UA’s capabilities for real-time field-level communication with TSN mechanisms offers the benefits of a single network and protocol all the way from the device level to the cloud regardless of the vendor.

An end user might be concerned about converged networks and might need the ability to use OPC UA to connect to the cloud over MQTT, for example. Cloud platforms today support an OPC UA connector, simplifying communication.

Regardless of the manufacturer of a machine, OPC UA companion specifications allow the machine to describe itself in the same way, with standardized semantics. ARC Advisory Group has written an informative blog on the subject.

Q: What topologies does OPC UA over TSN support?

A: Topologies that are commonly used in industrial networks are supported, including line, star, tree, and ring. TSN includes a standard mechanism for seamless, real-time redundancy implemented through cable redundancy, ring, or mesh topologies.

Q: Can OPC UA over TSN and OPC UA non-TSN devices be used in the same network?

A: Yes, because TSN is an evolution of standard Ethernet. TSN simply enhances standard Ethernet with real-time capabilities, so it is possible to have standard Ethernet devices and TSN devices present in the same network. Standard Ethernet devices would not need any interface/gateway to connect to a TSN network. However, only TSN-capable devices will be able to communicate in real time.

This FAQ appeared as a sidebar to our July cover story, "Not So Fast: TSN Not Quite Ready for Prime Time."

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