Assessment of OPC UA PubSub at Scale Using TSN Infrastructure and Network Calculus

OPC UA PubSub is a recent addition to the OPC UA industry standard used for machine-type communication in the Industrial Internet of Things. It can be combined with Time Sensitive Networking (TSN) to offer deterministic latency and bounded jitter. In this work, we model the network interactions between Credit-Based Shaper (CBS) and PubSub using Network Calculus. We derive worst-case delay bounds for various numbers of hops, payload sizes, and competing flows. The derived bounds are confirmed using deployments on commercial-of-the-shelf hardware and open-source solutions relying on a low-latency Linux kernel. Based on the results, we observe that the derived bounds are satisfied in all scenarios of seven hops with a round-trip-time (RTT) varying between 1 to 2.5 ms for respective payload sizes of 59 to 1481 B. Similarly, for jitter we observe fluctuations of $\pm \mathbf{250}\boldsymbol{\mu} \mathbf{s}$. Complementing the CBS results, we evaluate time-aware shaping, where we observe lower RTTs for average payload sizes of around $800 \mu\mathrm{s}$. Our contributions show that OPC UA PubSub applications can co-exist with TSN.