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TSN: an idea whose time has come?

01 February, 2018

Growing numbers of automation suppliers are throwing their weight behind an open technology known as Time-Sensitive Networking (TSN), which guarantees deterministic real-time data transmission between products from different suppliers, and promises to cut networking costs. Contributing editor Tony Sacks reports on the latest developments from the SPS IPC Drives show in Germany.

Time-Sensitive Networking (TSN) is being touted as the answer to the problems of synchronising high-speed industrial networks so that they perform reliably and deterministically in closed-loop control applications. The technology is being developed by the IEEE which is adding TSN to its Ethernet and wireless communications standards.

The potential attractions are significant. TSN will allow the use of open networks that support multi-vendor interoperability and bring together the worlds of OT (operational technology) and IT (information technology). In theory, TSN will support real-time control and synchronisation of high-performance machines over standard Ethernet networks, allowing both time-critical and standard communications to share the same network without interfering with each other or creating bottlenecks.

At the SPS IPC Drives automation mega-show held in Germany in 2016, a group of more than ten automation suppliers – including ABB, Bosch Rexroth, B&R, Cisco, General Electric, Kuka, NI, Parker Hannifin, Schneider Electric and SEW-Eurodrive – announced that they were backing the use of OPC UA over TSN as a unifying communication system for use between industrial control components, and with the cloud. The group predicted that the technology, based on open standards, would allow devices from different suppliers to interoperate seamlessly with each other and provide deterministic, real-time, peer-to-peer communications.

In the year since that announcement, the group has added several new members – including Phoenix Contact, Pilz, Sick and Wago – and at the most recent SPS show, at the end of November, they were able to demonstrate considerable progress in turning their TSN vision into a reality.

Over the past 18 months, TSN testbeds have been set up (under the auspices of the Industrial Internet Consortium) in the US and Germany, and more than 20 vendors of automation and communications technologies have taken part in events to test the interoperability of TSN products that they are developing.

The first fruits of this activity could be seen at the 2017 SPS where several suppliers were demonstrating TSN-compatible products at various stages of development. They included Beckhoff, Belden, B&R, Cisco, Hilscher, Moxa, National Instruments, Renesas, TTTech and Xilinx. (Some of these developments are outlined in the box, below/right).

Although the TSN-supporting companies include some eminent organisations, there are still some big-name absentees – notably, Siemens, Rockwell Automation and any of the Japanese automation manufacturers. But members of the consortium suggest that some of these companies are already working on TSN behind the scenes and may join the group formally at a later stage.

Certainly, Profibus & Profinet International (PI), the networking organisation most closely associated with Siemens, is working to incorporate TSN into Profinet. It announced this at the 2017 Hannover Fair, and at the SPS show, announced that the first findings of its TSN working group are now available, and that a road-map for the work on the specification has been drawn up.

PI points out that because TSN defines only the data link layer (level 2), Profinet, as an application protocol, should integrate seamlessly with TSN, allowing controllers and field devices to communicate with each other, and to exchange data.

PI believes that the ease of configuration of TSN network parameters will be a critical factor in how well it is accepted by users. The organisation argues that TSN will only be integrated easily if it uses a plug-and-work approach that avoids the need for extensive adjustments. PI is therefore primarily pursuing a decentralised configuration model, which allows the creation of flexible, efficient networks.

PI is aiming to publish its specification for using of TSN with Profinet by the middle of 2019.

Another networking organisation working to integrate TSN is the EtherCat Technology Group (ETG). It says that TSN will expand EtherCat applications to include “heterogeneous” network environments. It will allow industrial controllers to contact several different EtherCat segments in real-time via Ethernet. No changes to the EtherCat slave devices will be needed. TSN will also expand the EtherCat Automation Protocol (EAP) for communication between controls, resulting in more deterministic performance at this level.

The ETG is expanding its technology in the form of a profile which will avoid the need for any changes to the TSN standards. And, because the IEEE has not yet finalised its TSN specification, the use of a profile will also simplify adaptation to the final version of TSN. The ETG is a member of the IEEE committee drawing up the IEEE 802.1 specifications, ensuring that it will be able to access the specifications before they have been adopted formally. It will therefore be able to implement the technology at almost at the same time as the final TSN specification is published.

According to ETG, neither EtherCat device segments, nor EtherCat devices, will need to be modified to implement TSN. The stream adaptation function that connects an EtherCat segment to a TSN network can be placed either in the last TSN switch or in the first EtherCat slave device.

“The incorporation of TSN standards will significantly improve the real-time characteristics of generic Ethernet,” predicts Dr Guido Beckmann, chairman of the ETG Technical Committee. “With our technology expansion, we are making use of TSN in an ideal way, and exactly where TSN can offer significant advantages – in factory networks.

“As one frame is sufficient for EtherCat to communicate with a whole segment, and thus with the entire fieldbus network, EtherCat is virtually predestined for integration with TSN networks,” he adds. “We achieve this without turning our technology inside out. EtherCat together with TSN offers the ‘best of both worlds’. Therefore, this prepares EtherCat perfectly for the future.”

At the recent SPS show, the manufacturers in the group backing TSN were keen to stress their commitment to the technology. For example, Bernd Eschermann, head of technology in ABB’s industrial automation division, made the following pledge: “Whenever a new industrial product is developed by ABB that requires Ethernet-based real-time communication, we will make sure that OPC-UA over TSN is made available as a basic communication option. While the current focus is on controller-to-controller and upwards communication, we see an obvious advantage to use the same protocols down to the field level.”

And speaking on behalf of Schneider Electric, its chief technology officer, Fabrice Jadot, said: “We have a deep conviction that the development of a fully interoperable standard, based on OPC-UA TSN technologies and widely supported by the automation players, is the cornerstone and key differentiator to deliver to industry on the new requirements for increased flexibility, performance and maintainability.”

By the time the next SPS IPC Drives exhibition takes place at the end of this year, we should have a clearer idea of whether this enthusiasm is justified.

Automation manufacturers are testing the interoperability of their TSN Automation manufacturers are testing the interoperability of their TSN products using a pair of testbeds organised by the Industrial Internet Consortium – one in Germany, the other in the US

TSN products start to emerge

The recent SPS IPC Drives show in Germany was an opportunity to see some of the first TSN-supporting products in action. For example:

• Beckhoff was showing a bus coupler for its EtherCat I/O system that allows EtherCat segments to communicate with remote EtherCat controllers via Ethernet. The coupler uses TSN functions to minimise delays caused by Ethernet switches, and allows EtherCat I/O terminals and other EtherCat devices to be used on TSN networks. Beckhoff says that the coupler will combine the advantages of EtherCat (such as carrying numerous small packets of digital and analogue data) with those of TSN (which allows data streams to be defined for real-time, prioritised transmission across networks). Control systems will be able to address multiple EtherCat segments in real-time via TSN without needing to modify EtherCat slave devices. The coupler, placed as the first device in an EtherCat segment, contains one 100Mbit/s port that connects it to an Ethernet or TSN network, and another that can be used to integrate remote EtherCat devices.

• National Instruments demonstrated a pair of TSN-compatible products – an IP67-protected controller, and a TSN-enabled data acquisition system. The IC-3173 controller uses TSN for controller-to-controller communications, and is designed to act as an Industrial Internet of Things edge node in harsh locations, including spraydown manufacturing environments, without needing a protective enclosure. The CompactDAQ data acquisition system uses TSN to provide tight time synchronisation, thus simplifying and improving the scalability of distributed systems. The precise synchronised timing over the network eliminates the need for lengthy timing cables and ensures tightly synchronised measurements.

• The industrial computing specialist, Kontron, demonstrated a box PC controlling three motors that were synchronised via TSN. The PC was controlling the motors using a TSN card and TSN switches. At the same time, it was communicating with a primary server that was handling management functions via the OPC UA protocol. The PC could also be used to handle time-critical tasks locally, while data analysis is performed in the cloud. In this scenario, the PC would also handle motor control as well as processing time-critical data, thus acting both as a “fog” computer for edge analytics, and a gateway. Kontron has developed a TSN network card with a built-in switch for redundant networks with two or four Gigabit Ethernet ports. The PCI Express card allows PCs to be connected via a redundant ring-, line- or star-shaped TSN network, and can be used to add to TSN to existing PCs.

• The industrial networking manufacturer, Moxa, was demonstrating its first TSN Ethernet switch at SPS. Its aim is to equip customers with advanced networking infrastructures as they move towards Industry 4.0. “Time-sensitive networking is what factory automation needs,” says Moxa Networking product manager, Jack Lin. It means that “plant operators will no longer have to deal with different proprietary technologies”. The new technology, he predicts, will be “extremely beneficial for the manufacturing sector as it not only reduces overall costs, but also allows for more possibilities for innovation.”

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