In combination with Profinet, Time Sensitive Networks (TSN) can be a game changer in automation. However, the following questions need to be answered: What new applications and solutions are made possible? How do TSN standards contribute to this? What does the migration look like? And what will happen to the technology in the future?

New technologies always prove successful when they make new applications with major advantages feasible. One of these new applications is the use of artificial intelligence in automation. Usable computing power and tools that can be used for machine learning, image recognition or data mining, for example, are becoming ever cheaper and easier to use. ChatGPT is a good example of this. This development is expected to continue at a rapid pace.

What requirements does the use of AI therefore place on automation and networking? The following points need to be considered:

• Large amounts of data must be transported from the field to the AI.
• The result of the AI operation affects the process to be controlled.
• High-precision time synchronization is essential for processing and evaluating distributed data from the field level.

A concept in which all these requirements can be fulfilled in a single network is ideal. Profinet provides the solution with TSN.

Figure 2: TSN enables the integration of fieldbus and IT in a common network.

© Phoenix Contact

This example shows that there is considerable potential for improvement in combining all the necessary functions in a single network. This is usually referred to as a "convergent network" (Fig. 2). It is particularly important that the disciplines of the IT and OT worlds do not influence each other in a shared network. To ensure this, a number of optimizations must be made in Ethernet itself, collectively referred to as Time-Sensitive Networks (TSN).

TSN: Toolbox for special purposes

Figure 3: TSN is not a single standard, but a toolbox of mechanisms that make a shared network possible.

© Phoenix Contact

It is essential to understand that there is no single mechanism or standard behind TSN. Rather, TSN can be compared to a toolbox containing several tools. Each of these tools serves a specific purpose. The full benefits of a convergent network only unfold when all the tools work together correctly(Fig. 3). A brief explanation of the tools is provided here:

• Quality of Service (QoS): QoS is a well-known concept. Each telegram received at a switch, for example, is sorted into separate memory areas (so-called queues) based on an integrated priority field (VLAN priority), which are reused when sending according to their priority. QoS ensures that real-time critical traffic is not disturbed by other communication and is therefore the most important tool.
• Pre-emption: Another problem that can occur in a convergent network is the delay of real-time critical telegrams due to long TCP/IP telegrams. Pre-emption solves the problem by interrupting a long low-priority packet immediately when a high-priority packet is to be transmitted. The remainder of the low-priority packet still to be sent is saved and continued later. Pre-emption ensures that the variance of data forwarding at 1 GBit/s is reduced to around 1 µs - regardless of the telegram size.
• Precision Time Protocol (PTP, IEEE 802.1AS):Many applications in combination with artificial intelligence (AI) require high-precision time synchronization. However, the common synchronization protocol NTP (Network Time Protocol) is no longer sufficient. Synchronization accuracies in the µs range can be achieved using PTP because the runtimes on the lines and in the switches are measured and compensated.
• Synchronous communication: High-precision time synchronization via PTP also enables the synchronization of communication and applications in the devices involved. Without such synchronization, it is possible for the so-called terminal-to-terminal response time to vary over a wide range, as a cycle can always be missed on the way from the input to the output. Synchronous communication eliminates this.
• Brownfield integration: The use of the tools described requires new hardware in all devices involved. Therefore, TSN will initially only be introduced where there is a significant advantage. A smooth transition from Profinet RT to Profinet with TSN is feasible by using any existing Profinet device at the "boundaries" of a TSN area. In this way, investments in devices and know-how can be safeguarded.

With Profinet with TSN, the tools listed are used in a sensible combination. This results in advantages without changing the look and feel.