Tech Corner

By Kerstin Naser, Corporate Product Manager Wireless at Rutronik

5G + TSN: For the industrial automation of the future

There are numerous fieldbus standards aimed at ensuring real-time support, but none of them provide a manufacturer or platform-agnostic networking solution. An answer has been provided in the form of time-sensitive networking (TSN). Nevertheless, mobile applications using consistent real-time communication are possible when combined with 5G.

The Fraunhofer Institute for Production Technology (IPT) and a number of mechanical engineering, robotics and network engineering companies have recognized the potential to combine TSN with 5G. Together, they have developed a capable communication infrastructure with the aim of creating a high-availability, reliable and secure communications solution for sensors and actuators with cloud support. TSN provides real-time communications for wired communication, while 5G cellular technology handles all mobile and cloud connections.

One potential application would be the precise control of a robot and a tool, or of two robots working together during live production. Data processing can be outsourced to the cloud using this infrastructure, with the results sent back to the system. This enables robots in highly dynamic production systems to be controlled adaptively and flexibly without them needing to be connected directly to one another. This works with devices from a multitude of manufacturers, even using existing machinery and installations. There are numerous other scenarios that can also benefit from this combination, and some that perhaps may only be feasible with this constellation—among them autonomous driving, transport applications and remote surgery.

TSN for real-time Ethernet

Let’s first consider TSN, an evolution of standard Ethernet. Ethernet provides data communication services between devices from different manufacturers for IT purposes, namely in office environments. Industrial Ethernet is a more robust solution that is suitable for harsh environments. Special protocols such as EtherCAT, Profinet and Modbus TCP also provide a more deterministic environment— in other words, data packets are transmitted or received at predictable times, and the risk of data loss is eliminated.

However, what industrial Ethernet does not guarantee is real-time support. To this end, the IEEE 802.1 Task Group has developed a range of sub-standards referred to as time-sensitive networking (TSN). These standards define protocols for timing and time synchronization (IEEE 802.1AS) and for the configuration (IEEE 802.1Qcc in particular) and control of data traffic (traffic shaping and scheduling, IEEE 802.1CB, 802.1Qbu, 802.1Qbv among others). This means that there is a common plan that defines when data packets are forwarded in a prioritized fashion.

TSN does not cover all seven layers of the OSI model for network protocols, in which each layer defines how two systems communicate with specific tasks and functions. TSN addresses layers 1 and 2 and the real-time aspect, which covers the entire vertical length of the model. This means that more protocols are required for the higher layers. Businesses can continue to use their existing standards here, for example OPC UA. TSN provides the benefit of guaranteed real-time support without the need to adapt standards.

Interoperability and IT/OT convergence

Thanks to open standards, TSN enables manufacturer and platform-agnostic interoperability between different devices, machines and installations, similar to how standard Ethernet works in office IT. These standard Ethernet components can be integrated into TSN, allowing TSN to establish a consistent link between IT (information technology) and OT (operational technology) components. Critical and noncritical systems with different traffic classes can operate in the same network.

With bandwidths ranging from 10 Gbit/s to 400 Gbit/s—compared to the 100 Mbit/s commonly seen in industrial Ethernet networks—TSN also caters to the demands of increasingly large data volumes.

To date, only some of the TSN substandards have been ratified—others are still a work-in-progress. Even so, the existing standards can be implemented right away—they already guarantee real-time communication and can be adapted to future standards.

Real-time support now available wireless, thanks to 5G

5G enables real-time support to be expanded globally to wireless networks through TSN. 5G enables not only ultralow latency (ULL) and precise time synchronization, but also massive increases in reliability, range and bandwidth compared to its predecessor technologies, all with superior energy efficiency.

5G also enables the creation of private networks that are inaccessible to the public. They provide another substantial boost in performance, data protection and network security, as well as guaranteed quality of service (QoS). This is how 5G is laying the foundations for secure communication between a variety of machines and installations, robots and components—ranging from sensors and actuators to cloud services. When developing a TSN network, it is therefore recommended to consider integrating 5G support to ensure that you have a future-proofed, scalable solution.

Integrating 5G into a TSN network

Figure 1.

Figure 1 shows how TSN time synchronization (IEEE 802.1AS) can be integrated in compliance with 5G standards. The 5G system comprises a 5G base station (gNB) and a 5G core network (5GC) as well as multiple end devices (UE). One of these end devices (Reference UE) is connected to the wired TSN network as part of the reference system. This device must support IEEE 802.1AS so that it can be synchronized with the TSN clock via the Grandmaster.

The 5G system also has its own synchronization mechanism, where each 5G base station (gNB) synchronizes the end devices networked with it using the primary (PSS) and secondary (SSS) synchronization signals. The end devices use these signals to identify their wireless cell and radio frame; using specific synchronization algorithms, they can adjust for frequency and time differences. Each incoming System Frame Number (SFN) is also paired with the current time of the reference end device and transmitted to each connected end device. If OPC UA PubSub is used for distribution, all end devices connected to the base station can be synchronized.

The synchronization between the base station and connected end devices means that only the offset relative to the corresponding TSN time needs to be identified.

Figure 2.

Figure 2 offers an illustration of the message layers. The User Datagram Protocol (UDP) in combination with Multicast is used as the transport protocol so that every device in the Multicast group receives the subscribed messages.

As shown by Figure 3, the research team successfully used this arrangement with a synchronization interval of 31.25 ms to achieve synchronicity of 350 ns between an evaluation kit and an Intel NUC Mini PC.

Figure 3.