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.
Highlights
The data exchange process between modern industrial systems has attracted increased attention in recent years
This paper proposed a protocol converter that provides interoperability between the open platform communications unified architecture (OPC UA) publisher and data distribution service (DDS) subscriber
The JavaScript object notation (JSON) parser and message queuing telemetry transport (MQTT) were implemented by substituting JSONC and Mosquitto, which are commonly used in industry
Summary
The data exchange process between modern industrial systems has attracted increased attention in recent years. In the overall system integration, it is necessary to integrate multiple types of gateways, which provide the protocol interconversion function, and all automation levels into the same protocol To satisfy these requirements, the OPC Foundation pursues real-time connectionless mechanisms and has added the OPC UA publish–subscribe model (hereinafter PubSub), which is a new specification that supports the broker function used by MQTT and AMQP, to the OPC UA Part 14 standard [3]. The DDS provides quality of service (QoS) to ensure communication quality It sends and receives data based on topics that are virtual data transmission channels between a publisher and a subscriber. Topic-based application programming interfaces (APIs) for the data-centric publish–subscribe (DCPS) model provided by DDS include the following types [12]:. The topic can be read for each data writer inside the publisher and/or for each data reader inside the subscriber
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