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TSN and Pub/Sub

Real-time capability for OPC UA

OPC UA real time TSN2

Until now, OPC UA has had its limitations when it comes to complex processes with real-time requirements. This is why the OPC Foundation and the Industrial Internet Consortium (IIC) are working on two extensions that aim to give the OPC UA communication standard real-time capability: The first is a publish-subscribe model; the other is utilization of the IEEE 802.1 standard for time-sensitive networking (TSN).

B&R has tested the future OPC UA TSN standard intensively in cooperation with TSN network specialist TTTech. The tests revealed cycle times under two milliseconds and a jitter of 100 nanoseconds. Time-critical applications at the line level, such as synchronization of conveyor belts with various other equipment, can therefore be implemented without any problems. Additional information can be found in the following technical report OPC UA TSN – Field-tested, field-proven and in the interview "OPC UA TSN poised to replace conventional fieldbus".

OPC UA TSN is envisaged as the unified protocol for IIoT communication down to the controller level. At a joint press conference held during the SPS IPC Drives trade fair, the following announced their support for the standard: ABB, Bosch Rexroth, B&R, CISCO, General Electric, KUKA, NI, Parker Hannifin, Schneider Electric, SEW-EURODRIVE and TTTech. Additional information can be found in this press release.

Publish-subscribe model

Until now, OPC UA has used a client/server mechanism, where a client requests information and receives a response from a server. This system has its limitations in cases when there are many nodes on the network. The publish-subscribe model, in contrast, enables one-to-many and many-to-many communication. A server sends its data to the network (publish) and every client can receive this data (subscribe).

With a client-server mechanism, a client requests information and receives a response from a server.
With a publish-subscribe model, a server sends its data to the network (publish) and every client can receive this data (subscribe).

Real-time capability for standard Ethernet

The publish-subscribe model alone is insufficient for achieving OPC UA real-time capability. That's why the OPC Foundation is also implementing Time-Sensitive Networking (TSN). TSN is an extension of the IEEE 802 Ethernet standard to include various real-time functions. An exact timeframe in which data is transferred can also be specified.

Automotive industry is driving TSN development

With the automotive industry driving development of TSN, the required semiconductor components will be available very quickly and relatively inexpensively. The automotive industry would also like to handle all control tasks and applications that require functional safety over Ethernet. For this to be possible, they will need cycle times in the real-time range and deterministic network behavior.

Additional information concerning TSN can be found in this technical report about OPC UA TSN.

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