Evaluation and Extension of OPC UA Publish/Subscribe MQTT Binding

Abstract

Currently, Open Platform Communication Unified Architecture (OPC UA) is nominated as a reference standard to meet all Industry 4.0 demands with one protocol, enabling an efficient communication between devices in industrial systems. Recently, OPC UA has been extended by a publish/subscribe pattern to support multicast communication since there is a need for an efficient data aggregation and distribution to cope with the increasing number of controllers, sensors, and measured values in industries. Message Queuing Telemetry Transport (MQTT) is the most widely used publish/subscribe communication protocol and is based on a central broker for message exchange. In this paper, the communication latency of OPC UA end devices exchanging data over MQTT as a broker-based middleware is investigated and compared to the client/server-based communication. In particular, we analyze the use case of one-to-many communication for a crane model from the material handling domain. We provide a prototype implementation of the OPC UA MQTT extension and our evaluation results show the reduced traffic overhead and communication latency compared to client/server-based communication.