Real-time capability is required in many places for the strict synchronization of movement processes in industrial applications. To ensure this, predictable time behavior is at least as important for data transmission as a sufficiently high data rate. In view of the constantly increasing data volumes in machines and systems, it makes sense to make Ethernet usable for industrial applications. The leading standard for networking computers in office environments offers a high transmission bandwidth. In addition, the TCP/IP standard enables uniform data communication across the boundaries of individual networks.

Machine and plant manufacturers and automation specialists were particularly attracted to Ethernet by the availability of inexpensive, mass-produced hardware. However, the system developed for office environments does not have the deterministic time response that some industrial applications require.

Digitization brake on protocol diversity

To enable predictable real-time behavior with isochronous cycle times of less than one millisecond, manufacturers of automation systems created their own real-time protocols. The variants of Industrial Ethernet, which differ from the Ethernet standard and are essentially proprietary, are not compatible with each other or with surrounding networks. Industrial Ethernet is therefore essentially limited to the machine and field level. Ethernet-based fieldbus systems enable the fast transmission of large amounts of data, such as image and vibration data. They also allow the transport of safety-related data on the same lines using "black channel technology". Nevertheless, the variety of incompatible protocols prevents the free use of machines and devices in shared networks and represents a major hurdle on the path to the digitalization of production.

Advancing miniaturization in electronics has broken down the previously rigid division into control computers and peripherals. As sensors and actuators are increasingly equipped with their own processors, the number of self-intelligent network nodes at field level is growing rapidly. A prerequisite for their universal networking is an open and real-time capable communication protocol. Open Platform Communication Unified Architecture (OPC UA) in accordance with IEC 62541 is an industrial communication protocol that can be used to semantically describe data in a machine-readable way. It is manufacturer-independent and has a high level of inherent security. The open communication protocol OPC UA enables fully consistent and transparent communication from the sensor to the cloud.

OPC UA owes its high popularity and rapid spread primarily to an integrated introduction mechanism. This function gives the protocol the ability to communicate with devices added to the network at a later date without having to take them into account during the original programming. This significantly reduces the effort required for conversions and modernizations and thus contributes to the future-proofing of production facilities. It is also an essential prerequisite for the ability of production machines to plug & produce in the same way as plug & play office equipment. However, OPC UA does not have deterministic time behavior either. Like standard Ethernet, it is therefore not readily suitable for the transmission of real-time data within synchronized plant components.

With Pub/Sub and TSN to the new Ethernet

For this reason, the OPC Foundation introduced the fast Publisher-Subscriber (Pub/Sub) communication model as a first step. It dispenses with the need to wait for responses from recipients between individual messages. Even continuous data transmission with OPC UA Pub/Sub significantly speeds up communication and reduces the load on the network. However, the ability to achieve deterministic, hard real-time behavior only arises through a uniform time base.

The Institute of Electrical and Electronics Engineers (IEEE) created such a uniform time base with the Ethernet standard Time Sensitive Networking (TSN). This extension of the Ethernet standard regulates the transmission behaviour of data packets by means of time synchronization via a uniform time base, scheduling of data transmission (traffic scheduling) and automated system configuration. Only the combination of OPC UA Pub/Sub with TSN makes it possible to implement real-time-capable applications in an industrial environment on the basis of generally available standards. It guarantees the deterministic transmission of data in large convergent networks and can eliminate the previous separation of machine and IT networks.

In 2018, 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. It thus laid the foundation for overcoming the previous compatibility deficiencies. The redefinition of Ethernet also resulted in significant performance improvements. The technology enables networks with several 10,000 nodes that can communicate up to 18 times faster than with all previous protocols and are also very easy to manage and configure. Among other things, this opens up completely new application possibilities for highly synchronized drive technology, also coupled with digital image processing.

For the secure and trustworthy exchange of data in the network, OPC UA over TSN offers the option of using digital certificates in accordance with the X.509 standard, thus ensuring a high level of security. In contrast to the Industrial Ethernet of the past, OPC UA over TSN is a completely manufacturer-independent protocol with open-source software implementations. These are managed and tested by the Open Source Automation Development Lab (OSADL), among others. This makes system integrators and users independent of individual providers when it comes to communication.

New standard for data communication

By adding the real-time capability of TSN, the protocol enables the merging of IT and OT into a common network and thus forms the basis for all applications in the IIoT. The manufacturers of processor or controller modules are equipping more and more products with TSN capability as standard. This is facilitated by the integration of TSN functionality in semiconductors from numerous manufacturers. This simplifies the implementation of convergent Ethernet-based networks on which time-synchronized, deterministic communication takes place in parallel to regular IT data traffic.

This makes it possible to create real IIoT applications for Industry 4.0 based on universally valid Ethernet protocol standards. The additional costs for TSN capability will decrease the more this is shifted to the chip level. As a result, it is to be expected that newly installed networks will already have real-time capability in the standard in the near future. Automation engineers as well as planners, operators and maintainers of in-house networks, but also manufacturers of automation and information technology, are therefore increasingly relying on Ethernet with TSN.

The universal communication platform is in the process of establishing itself as a universal standard for all forms of electronic data communication, even beyond industrial networks. End devices without TSN capability can also be operated via TSN networks without any disadvantages. Sooner or later, Ethernet switches will be equipped with TSN through corresponding chips in the standard and will generally give Ethernet real-time capability. This will eliminate the current high effort required to overcome compatibility limits as an obstacle to integrating time-critical system components into the Internet of Things.

Thomas Kruse, Product Manager Network Technology, Smart Home and Security, Reichelt Elektronik