TSN in Automation: Where Are We Now?

Ethernet was introduced to the office world in the early 1980s and quickly gained popularity due to its incredibly high (for the time) throughput of 10 Mbps. However, this Ethernet was not practical for real-time applications because it used a common medium called a "party line." This was prone to collisions under high utilization, causing problems in office settings.

Later, with the development of Ethernet, the conflict problem was solved by introducing switching networks. In addition, Ethernet data message priority was introduced through Quality of Service (QoS).

For industrial applications, it is particularly important to guarantee low latency. Despite QoS, standard Ethernet used in office environments can only guarantee latency down to a certain point, especially under high network utilization.

This is due to many reasons, but the main ones are the store-and-forward strategy commonly used in commercial multi-port switches and the fact that it is not possible to reserve bandwidth.

Switch cascading has posed challenges for industrial environments from the beginning. In addition to the star topology used in the IT field, line, ring and tree topologies are also commonly used in the automation field. These adjusted topologies significantly reduce the wiring requirements and costs of Ethernet installations. Therefore, in industrial applications, two-port switches with a cut-through strategy are integrated into field devices. Cut-through means that the data message is forwarded before it is completely received.

Figure 1. Ethernet frame: Data fields relevant to TSN data stream identification are shown in green

Figure 2. Topology

It must be ensured that there is always enough bandwidth (and buffer space) available for high-priority datagrams. Standard Ethernet cannot currently do this.

Since conventional Ethernet does not have sufficient bandwidth reservation capabilities, automation experts have been developing their own versions of Ethernet since 2000. However, they have taken different development paths.

Figure 3. Timing model: PHY, cables and switches affect data transmission latency. This must be taken into account when using the time slot approach (PROFINET IRT and TSN Time Aware Shaper (TAS))

These standards require special hardware to support, and therefore require the use of special ASICs. PROFINET RT and EtherNet/IP® are no exception in this regard, as they are also based on embedded two-port cut-through switches. Flexible, hardware-based multiprotocol solutions such as ADI's fido5000 solve this problem in a streamlined manner.

With TSN, the industry has successfully developed an extension of standard Ethernet in accordance with IEEE 802.1 that has successfully broken free from the limitations of the past. As a result, the standardized layer 2 in the ISO seven-layer model is now upwardly compatible with previous Ethernet and hard real-time functions. With 802.1AS-rev, TSN also defines an interoperable and uniform method for synchronizing distributed clocks in the network. Since "best effort" communication is always possible with TSN, it is possible to share cables in hard real-time applications and all other applications (web servers, SSH, etc.). In this respect, TSN is no different from PROFINET IRT and it also provides similar performance.

The additional requirement for adopting TSN is the need for a wider range of network configurations. Both centralized and distributed configurations are possible. Both types of configurations are currently being discussed and implemented. Future developments are aimed at achieving interoperability between the two configuration mechanisms.

The most common answer is that it offers the lowest-cost network interface on the market and is applicable to a wider market. After all, TSN can also be used in the future building automation and automotive industries. In fact, the market size of embedded TSN solutions is expected to be significantly larger than the current market for all industrial Ethernet solutions combined.

The biggest technical advantage of TSN over previous industrial Ethernet methods is its scalability. Unlike current industrial networks, TSN is not defined for a specific transmission rate. TSN can be used for 100 Mbps, as well as 1 Gbps, 10 Mbps, or 5 Gbps.

It also allows for better optimization of the topology, since now the appropriate data rate can be selected for each segment. Whether 1 Gbps, 100 Mbps or 10 Mbps, a uniform layer 2 – IEEE802.1/TSN – is used.

A uniform network infrastructure also facilitates the task of setting up and maintaining networks, because with TSN, solutions can now be used in areas other than automation, such as building, process and factory automation, and energy distribution.

This brings us to the next advantage, the training factor. TSN is already a topic at many universities, mostly still in the research phase. However, technical and vocational colleges have shown great interest in the subject. We can say with a fair degree of responsibility that TSN will become essential basic knowledge for engineers, technicians and skilled workers. Retraining for different fieldbuses will no longer be necessary.

In almost all TSN-related working groups, one recurring theme is: How can the transition to TSN and the supply of existing installations (e.g. “brownfield” applications) be ensured at the same time?

In all aspects, emphasis is placed on making the transition to TSN easy and smooth for customers. Today, we can safely say that existing Industrial Ethernet protocols will not disappear overnight. On the contrary, anyone currently using PROFINET, EtherNet/IP, EtherCAT or similar popular Industrial Ethernet protocols can safely assume that in 10 years they will still be able to run networks using these protocols and get support and replacement parts.

All Industrial Ethernet organizations provide models to describe how existing plants can work with new TSN-based devices. The interface to the existing industrial network consists of a gateway (Sercos), an interface with a coupler (EtherCAT) or without any special hardware (PROFINET RT). In particular, PROFINET and EtherNet/IP plan to use their complete protocol as layer 2 for TSN.

This enables a gradual transition to TSN.

Figure 4. Brownfield: TSN network combined with PROFINET and EtherCAT

In short, TSN will be ubiquitous in new installations and will gradually be introduced into existing installations in the form of islands or segments.

However, along with TSN, new protocols will emerge in the field of Industrial Ethernet. OPC UA with the new transmission protocol PUB/SUB, together with TSN, has been seen as a competitor to traditional protocols. For manufacturers of field devices, this means that they have to support traditional Industrial Ethernet solutions as well as TSN and new protocols at the same time.

ADI acquired Innovasic, a leader in Industrial Ethernet, more than a year ago and has now successfully integrated it. With the integration of Innovasic, the fido5000 series of industrial dual-port switches have been incorporated into the ADI product line. The switches support all relevant Industrial Ethernet protocols and are TSN-ready.

With fido5000, it is possible to plan products to transition to TSN today and at the same time meet current requirements (PROFINET IRT, EtherCAT, POWERLINK, EtherNet/IP, etc.). With fido5000, it will also be possible to implement OPC UA PUB/SUB. With fido5000, TSN can be planned as an update to existing systems.

The fido5000 series is still being enhanced. We will provide new products for 1 Gb applications, but 10Mb/100Mb products will continue to be provided to meet customer requirements.

The fido5000 series provides flexibility to perform TSN migration reliably and efficiently.

TSN makes it possible to create a unified foundation for all industrial communications. Once TSN is introduced, layers 1, 2, and 3 of the ISO seven-layer model in industrial applications will be unified. This has the potential to enable entirely new levels of scalability and performance.