According to the principles of Industry 4.0, reliable data communication with high data rates and deterministic time behaviour is one of the requirements for production. Time Sensitive Networking (TSN) expands the Ethernet standard to include hard real-time capability, enabling IT and OT to be merged into one standardised, shared network without the previous incompatibility issues.
The invention of the mechanical clock enabled the concept of time as a central principle of modern society. The resulting benefits include making it significantly easier to synchronise to the second and to control movements, work processes and workforces in factories. American architect and philosopher Lewis Mumford (1895 – 1990) therefore considered it to be the key invention of industrialisation.
In many places, real-time capability is a prerequisite for the rigorous schedule coordination of movement processes in industrial applications. To ensure this, predictable time behaviour is at least on a par with a sufficiently high data rate when it comes to data transmission.
Ethernet for industrial applications in one network
The logical response to constantly increasing data volumes in machines and systems is to make it possible to use Ethernet for industrial applications too. The leading global standard for networking computers in office environments offers high transmission bandwidth. In addition, the TCP/IP protocol suite enables global standardised data communication beyond the borders of individual local networks.
Mechanical engineers, plant engineers and automation engineers alike were especially attracted to Ethernet by the availability of mass-produced, affordable hardware. However, the system developed for office environments does not feature the deterministic—i.e. precise, predefined—time behaviour that is required in many industrial applications.
Putting the brakes on digitalisation and protocol diversity
Automation system manufacturers created their own real-time protocols to enable predictable real-time behaviour with isochronous cycle times below one millisecond. These variants deviate from the Ethernet standard and are essentially proprietary variants of Industrial Ethernet. As they are not compatible with each other or with surrounding networks, Industrial Ethernet therefore remains predominantly restricted to machine and field level.
The quick transmission provided by Ethernet-based fieldbus systems can handle large data volumes and therefore comprehensive information such as image and vibration data. In addition, it allows safety-related data to be transported on the same lines via black channel technology. Nevertheless, the variety of incompatible protocols prevents unrestricted use of machines and devices in shared networks and is a considerable hurdle on the path to the digitalisation of production.
Manufacturer-independent communication
Ongoing miniaturisation in microelectronics has eliminated the previously fixed division into control computers and dumb peripherals. As sensors and actuators are increasingly equipped with their own processors, the number of intrinsically intelligent network nodes at field level is increasing rapidly. An open communication protocol that is simultaneously real-time capable is a prerequisite for the universal networking of these components.
IEC 62541 states that Open Platform Communication Unified Architecture (OPC UA) is an industrial communication protocol that can describe machine data semantically in such way that it can be read by machines. It is manufacturer-independent and features a high degree of inherent security. As such, the OPC UA open communication protocol enables fully uninterrupted and transparent communication from the sensor to the cloud, unlike the incompatible protocols of Industrial Ethernet.
Unrestricted interoperability
OPC UA primarily owes its great popularity and quick spread to an integrated introduction mechanism. This feature enables the protocol to communicate with devices that are subsequently integrated into the network, without having to allow for these additional devices during the original programming. This significantly reduces the outlay for conversion and modernisation measures and therefore boosts the future security of production systems. It is also a key requirement for the Plug & Produce capability of production machines, similar to Plug & Play in office devices.
However, OPC UA also does not provide deterministic time behaviour. As with standard Ethernet, it is therefore not suitable for the transmission of real-time data within synchronised system parts.
Pub/Sub and TSN for new Ethernet network
Consequently, the OPC Foundation started by establishing the quick publisher–subscriber communication model (Pub/Sub). This does away with the need to wait between individual message responses from the receivers. The continuous data transmission with OPC UA Pub/Sub has already significantly speeded up communication and relieved the network.
However, the capability for deterministic hard real-time behaviour first requires a standardised time basis. With regards to the fourth industrial revolution that was proclaimed ten years ago in 2011 at Hannover Messe, this is on a par with the mechanical clock mentioned earlier as the prerequisite for the first industrial revolution.
The Institute of Electrical and Electronics Engineers (IEEE) created one such standardised time basis in the form of Ethernet standard Time Sensitive Networking (TSN). This expansion of the Ethernet standard regulates the transmission behaviour of data packages by time synchronisation via a standardised time basis, disposition of the data transmission (traffic scheduling) and automated system configuration.
The combination of OPC UA PubSub with TSN communication technology has broken new ground by enabling the implementation of real-time capable applications in an industrial environment on the basis of commonly available standards. It guarantees the deterministic transmission of data in large convergent networks and can close the previous gap between machine and IT networks.
High performance alongside security
With this in mind, the OPC Foundation presented OPC UA including TSN down to field level as a universal, real-time capable communication platform from the cloud to sensor level at the SPS IPC Drives 2018 trade fair in Nuremberg. By doing this, they laid the foundation for overcoming the previous incompatibility issues.
Significant performance improvements were also made as part of this redefinition of Ethernet. The technology enables networks with more than 10,000 nodes, which can communicate up to 18x faster than with all previous protocols and which are also extremely easy to manage and configure. Among other things, this opens up completely new application possibilities for highly synchronous drive technology, including when paired with digital image processing, for example.
OPC UA over TSN makes it possible to use digital certificates according to the X.509 standard to securely and reliably exchange data in the network, ensuring a high degree of security. Unlike the Industrial Ethernet of the past, OPC UA over TSN is a fully manufacturer-independent protocol with open-source software deployment. The Open Source Automation Development Lab (OSADL) is one of the bodies that manages and tests this. As a result, system integrators and users are independent of individual providers when it comes to communication.
New global standard for data communication network
Adding the real-time capability of TSN enables the protocol to merge IT and OT into one shared network, laying the foundation for all applications in the IIoT.
Manufacturers of processor and controller modules are increasingly equipping products with TSN capability as standard — a task that is made easier by the integration of TSN functionality in semiconductors from numerous manufacturers. This simplifies the realisation of convergent Ethernet-based networks, which also carry time-synchronised, deterministic communication alongside regular IT data traffic.
It is therefore possible to easily create real applications of IIoT for Industry 4.0 based on universal Ethernet protocol standards. The more TSN capability is transferred to chip level, the lower the added costs become. It is consequently likely that newly installed networks will boast real-time capability as standard in the very near future. Automation engineers, planners, operators and maintenance technicians of in-house networks as well as leading manufacturers of automation and information technology are therefore increasingly reliant on Ethernet with TSN.
Opening the door to Industry 4.0
The universal communication platform is in the process of establishing itself as the universal global standard for all forms of electronic data communication beyond industrial networks. End devices without TSN-capability can also be operated without detrimental effects via TSN networks. Ethernet switches will eventually be equipped with TSN as standard through the use of corresponding chips and will generally give Ethernet real-time capability. This will eliminate the currently still high expense of overcoming compatibility limits as a hurdle in integrating time-critical system parts in the Internet of Things. This foundation can make the concepts of Industry 4.0 a reality.
No jitter, no bug
The jitterbug is a fast-paced swing dance. In IT, however, the bit offset (or jitter) is the deviation of individual bits in a data package from their (temporary) nominal position. In a play on words, many people refer to an error (bug) caused by this as a “jitterbug”. Adding TSN to Ethernet reliably ensures extremely low values for the jitter, preventing these bugs.
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