Two mechanisms described for data exchange are: –
The first mechanism is a client-server model where UA clients are used in the dedicated services of the UA server. The second mechanism is a publisher-subscriber model where a UA server is making a configurable subset for information to be available to any number of listeners.
The mechanisms defined above are detached from the actual protocol. TCP and HTTPS are available for the client-server. UDP, as well as AMQP and MQTT, are available for the subscriber model. As defined above, both variants are required:
The context for peer-to-peer is for secure, confirmed transport with restriction in several connections.
The distribution for broadcast is under the aspect of “fire and forget”.
OPC UA can be combined both with AMQP or MQTT. But a device that is resource-constrained with MQTT only should be able to handle its data in OPC UA via MQTT as per the information model format.