Experimental Characterization of Asynchronous Notification Latency for Subscriptions in OPC UA

The past few decades saw factory and process automation move from monolithic to fully distributed architectures, where the communication system plays a key role in providing higher flexibility and availability, yet fitting the peculiar requirements of such contexts. As part of the Industry 4.0 (r)evolution, the Industrial Internet of Things is meant to achieve full convergence toward well-agreed non-proprietary digital networking technologies. In this scenario, OPC UA is becoming increasingly relevant as a high-level protocol to exchange information in heterogeneous distributed industrial applications. In this paper, the performance of OPC UA has been evaluated by means of an experimental measurement campaign carried out on real devices connected to real networks. In particular, we analyzed how much the end-to-end notification latency achieved by the subscription mechanism is affected by the position and interconnection of devices, their specific implementation, and configuration parameters. Outcomes can be helpful in designing systems where industrial devices interact with local workstations, the edge, and the cloud, to understand whether or not timing constraints of applications will be met.