Data Distribution Service Converter Based on the Open Platform Communications Unified Architecture Publish–Subscribe Protocol

Abstract

The open platform communications unified architecture (OPC UA) is a major industry-standard middleware based on the request–reply pattern, and the data distribution service (DDS) is an industry standard in the publish–subscribe form. The OPC UA cannot replace fieldbuses at the control and field levels. To facilitate real-time connectionless operation, the OPC Foundation added the publish–subscribe model—a new specification that supports broker functions, such as message queuing telemetry transport (MQTT), and advanced message queuing protocol (AMQP)—to the OPC UA Part 14 standard. This paper proposes a protocol converter for incorporation into the application layer of the DDS subscriber to facilitate interoperability among publisher–subscriber pairs. The proposed converter comprises a DDS gateway and bridge. The former exists inside the MQTT and AMQP brokers, which convert OPC UA publisher data into DDS messages prior to passing them on to the DDS subscriber. The DDS bridge passes the messages received from the DDS gateway to the OPC UA subscriber in the corresponding DDS application layer. The results reported in existing studies, and those obtained using the proposed converter, allow all devices supporting the OPC UA and OPC UA PubSub standards to realize DDS publish–subscribe interoperability.