Time-Sensitive Networking: the factory’s traffic cop

Wireless technologies can make production halls more efficient and more dynamic, but this involves a huge challenge: All data must arrive in the right place at the right time. Could Time-Sensitive Networking provide a breakthrough in this area?

When you step inside a factory building, you enter a world that operates according to its own specific rules: strict production processes, rigorous quality control, modern machinery, and a highly specialized workforce. One cog engages with the other, and one action determines the next – always with a view to speeding up production. For example, with conveyor belts for transporting components, a camera hangs above the belt and casts a critical eye over every object that passes. If the camera spots a defect, a jet of compressed air is immediately activated to eject the flawed component into a waste bin. This time, however, something goes wrong: The data are not transmitted in time, the jet of compressed air fires into thin air, and the belt must be stopped. All it takes is one brief moment to bring this world, with all of its specific rules, to a standstill.

Production downtimes of this kind are costly. In response, manufacturing and industrial companies are always looking for a decisive boost in efficiency that allows the cogs to engage more effectively – and this search quickly leads them to the field of wireless communication. After all, in contrast to the wired connections that have dominated until now, wireless communication carries significantly lower maintenance and repair costs. What’s more, wireless technologies can reach into the most distant corners of a production hall, allowing the integration of mobile elements such as automated mobile robots (AMRs) or automated guided vehicles (AGVs) that move through a factory autonomously and transport materials. Suddenly, there is a hint of dynamism in the otherwise rigid processes of industrial communication, speeding up production and making it more flexible. As always, however: with great opportunities come great challenges.

Green light, red light

Frank Burkhardt knows all too well what this means in practice. As manager of the Industrial Communications group at Fraunhofer IIS, he has been studying real-time wireless communication in the production environment for many years. Through this work, he and his team have achieved ever greater speeds and pushed latencies further and further down into the range of microseconds. At some point, however, it became clear that this wasn’t enough. “Fast wireless communication isn’t much use if the network behind it isn’t deterministic,” says Burkhardt. This means that all data must reliably arrive in exactly the right place at exactly the right time – even when faced with increasing dynamism, mobility, and unpredictability in a factory setting. With this in mind, Burkhardt is now researching a technology known as Time-Sensitive Networking (TSN), which combines wireless communication and determinism.

If you want to understand how TSN works, the first thing is to imagine the antithesis of the production environment: a fictional city where there are neither traffic lights nor traffic rules nor road signs. Cars block each other’s paths at intersections, the law of the jungle dominates, horns are blaring everywhere – the situation descends into chaos. Chance and whim now decide which vehicle reaches its destination punctually and whether ambulances can get emergency patients to the hospital on time or instead get stuck in traffic. No one would want to live in a city like this.

Leaving the fictional city behind, let’s turn our minds back to the factory. Here, it’s not vehicles driving to a destination, but rather packets of data. “Talkers” transmit their data, which then travel to data intersections via “bridges” and are ultimately received by “listeners.” With Time-Sensitive Networking, there is now a central authority – a sort of traffic cop – that assigns each data packet a traffic light of its own. By switching these lights to green or red, it decides which packet can pass through the intersection and when. Just as there are vehicles whose punctuality takes special priority in traffic (such as the ambulance carrying an emergency patient), there are also data packets that are so vital to processes in the production hall that they cannot afford to be late.

Everything that is mission-critical or safety-critical is therefore given priority of passage. Examples include the compressed air that is intended to remove a defective component – because production will otherwise come to a standstill – or a moving AGV that must apply the brakes in good time if an employee is approaching and there is a risk of a dangerous collision. “TSN books various time windows, assigns a traffic class to the data packets according to their relevance, and guarantees a specific data rate for each traffic class,” explains Burkhardt. “This time synchronization then results in fixed timing.”

Dynamism as the crowing achievement

The research that Burkhardt is pursuing at Fraunhofer IIS aims to examine how all of these detailed parts can work together smoothly as a whole – because the conflict between increasing mobility and a static environment is yet to be fully resolved. “Dynamic processes within a deterministic network are a critical issue,” says Burkhardt. Factories normally have a fixed network topology – in other words, the data from machines and devices are always transmitted to their controller via a fixed route. Mobile elements defy this logic, however, in that they force a degree of variability that was not previously envisaged in the system.

For example, if an autonomous mobile robot starts moving and departs from its usual radius, a base station from another sector must pick up the baton and take over connectivity. “We’re currently exploring how a handover between base stations can take place using Time-Sensitive Networking,” says Burkhardt. These rapid handovers could also boost the resilience of the overall network. After all, a good traffic cop not only works preventively to avoid logjams, but also deftly diverts traffic via alternative routes if one of the intersections collapses unexpectedly. Individual downtimes and disruptions would then be less detrimental to production.

High hopes are resting on Time-Sensitive Networking – and there is particularly frequent mention of IT/OT convergence, whereby data-intensive applications from information technology (IT) and the time-critical applications from operational technology (OT) could be brought together using TSN. A closed production island, highly efficient processes, and rapid adaptation to new market conditions might be just the beginning. “Once wireless communication is deterministic, you can think further down the line, and suddenly a whole series of new visions open up,” says Burkhardt. Every machine with its own base station, AGVs whizzing through the hall as mobile base stations, hyperconnectivity, 6G, the network of networks – and, in the midst of all this, a traffic cop making sure that everything runs as it should.