With the coming of 5G technology and the implementation of 10+ GbE networks in factories, real-time data processing for OPC UA and other tactile Internet applications is emerging as an important new area of use. By Zeljko Loncaric, marketing engineer, Congatec AG
Time-Sensitive Networking (TSN) technology is paving the way for these connected real-time applications, and will also impact established proprietary Industrial Ethernet installations.
Although fieldbuses will continue to play an important role in the coming years as industrial communication systems, they are less significant for industrial IoT and Industry 4.0 applications.
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That is because IoT and Industry 4.0 automation and process control technologies have high bandwidth and performance demands, require cloud and fog connectivity at the edge and rely on vertical data exchange to the top levels of the automation pyramid, which is, of course, difficult to achieve with classic Fieldbus installations.
Higher demands and the gradual introduction of industrial PC technology have led to the replacement of the established Fieldbus – once the most important industrial communication system – by a new, ‘second’ Fieldbus generation: Industrial Ethernet.
According to an HMS market study from 2019, around 59 per cent of newly installed nodes for factory automation support Industrial Ethernet, while only around 35 per cent of new nodes are connected via a classic Fieldbus system.
In Industrial Ethernet applications, real-time and IT data ideally share a common transmission medium. Unlike most Fieldbus applications, there is practically no limit to the number of connected devices or the size of the network.
At the same time, seamless and unified network connectivity guarantees data continuity across the entire production area, which can be secured and tightly controlled via security protocols and IT security management.
Given the appropriate gateways, classic fieldbuses can, of course, still be used as subordinate networking systems in the field.
Previous Dominance Of proprietary Standards
But just like the many different Fieldbus systems, current Industrial Ethernet variants do not come in a uniform standard. Instead, there are various proprietary solutions that are incompatible with each other.
This is not really surprising since the standards of this second Fieldbus generation were developed by the same companies and interest groups as the predecessors, and individually adapted to the desired requirements – a process that had already led to a large variety of different standards for the first generation of fieldbuses.
From Ethernet To Industrial Ethernet
However, for the developers of the second Fieldbus generation realising real-time communication, divided into real-time classes with different response time demands, meant a major challenge – and this applied to all variants.
This was down to the fact that conventional IEEE 802.3 compliant IT Ethernet does not support deterministic transmission, despite providing comparatively high transmission rates.
The resolution of data collision issues is guided by a mechanism that is based on the random principle, which can lead to irregular delays in data traffic. Real-time capable Ethernet solutions prevent such collisions by introducing their own, significantly leaner real-time protocol stacks.
These are marked by a so-called ‘EtherType’ in the Ethernet protocol layer and prioritised accordingly.
The seamless Ethernet connectivity required for ‘normal’ TCP/IP communication (emails, web servers, etc.) is guaranteed since less time-critical data can be tunnelled in parallel over a so-called mailbox channel without disturbing the real-time traffic.
Hard Real-Time
While soft real-time applications tolerate larger signal propagation delays relatively generously, hard real-time requires exact deterministic response times, often with near-zero delays and clock cycles down to the µs range.
Synchronisation must always be timed precisely. Hard real-time Ethernet communication with guaranteed latency, therefore, requires exact time synchronisation of all nodes involved in the communication.
However, the Network Time Protocol (NTP) used to set the date and time on computers is not suitable for such real-time synchronisation. This is why modern Fieldbus systems use the IEEE 1588 Precision Time Protocol (PTP), which synchronises the clocks on different nodes (master, slaves) with two-digit nanosecond precision.
But for this purpose, PTP must be integrated into the hardware of the involved network interfaces, otherwise, the synchronisation can be distorted.
To accomplish such real-time operating behaviour between the individual nodes, the different Industrial Ethernet variants have so far relied primarily on proprietary hardware or specific protocol extensions.
This has contributed to the multiplication of mutually incompatible Industrial Ethernet standards and intensified the call for open and interoperable standards for real-time Ethernet communication – especially in view of the trend towards IIoT and Industry 4.0 connected factories, which in a sense define their own new layer in the automation pyramid and demand standardised data exchange using real-time protocols such as OPC UA.
In addition, tactile Internet applications are emerging as an important new area of use, made possible by the availability of 5G technologies and 10+ GbE networks in factories, autonomous (logistics) vehicles and energy grids.
Tactile Real-Time Internet With TSN
The goal is now increasingly within reach. A TSN task group within the IEEE 802.1, which has been working on improving the real-time behaviour of commercial networks, has already published several IEEE standards for this purpose, such as IEEE 802.1Qbv, which enables precise scheduling of network traffic via time slicing process using a so-called time-aware shaper (TAS).
The IEEE 802.1AS TSN standard, in turn, implements profiles of the above mentioned IEEE 1588 PTP for the cyclic synchronization of TSN nodes. This solution has now become suitable for industrial use, with IEEE 802.1AS already integrated as a PTP basis for hard real-time applications in the standard Intel i210 and i219 Ethernet controllers and therefore available as a standard component.
Congatec, for example, uses the i210 on a Pico-ITX board with Intel Atom E3900 processors and has already implemented a proof of concept (PoC) for the integration of the TSN protocol in accordance with the IEEE 1588 PTP specification.
This integration also ensures real-time capability in the upper layers of the communication protocols in order to support solutions such as MQTT, DDS or OPC UA and other industrial Ethernet protocols.
The PoC comprises several conga-PA5 Pico-ITX boards, streaming a high-resolution video file as the Ethernet base load while generating and transmitting real-time critical data in parallel.
In the demo, the IEEE 1588 PTP synchronisation can be turned on or off via a digital switch to measure and display the different communication behaviour of distributed devices and fog servers over Ethernet.
The PoC proves that the maximum jitter can be reduced to the high-precision nanosecond scale despite large network loads. That is everything set for the tactile Internet.
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