Glossary · Industrial communication
OPC UA PubSub
Also known as: OPC UA Publish-Subscribe
German: OPC UA PubSub
In industrial communication, OPC UA PubSub is the publish-subscribe communication model of OPC UA, specified in OPC 10000-14, in which publishers send data set messages to any number of subscribers, either brokerless over UDP multicast or via a message broker such as MQTT or AMQP.
- Industrial communication
- Standards
In one sentence
OPC UA PubSub (OPC 10000-14) distributes OPC UA data one-to-many, over UDP multicast or via MQTT and AMQP brokers.
Example
Twenty energy meters publish their measurements as OPC UA PubSub messages over MQTT to a cloud broker, where an analytics service subscribes.
Explained in context
Context cards connect this term with others to answer one question. Also in British English and German.
How it applies
- Engineering: PubSub complements client-server: it suits many receivers, low-power or cyclic data exchange, and cloud connections. Data sets and their metadata define which values are sent.
- Real time: Over UDP with Time-Sensitive Networking (TSN), PubSub is the basis of deterministic controller-to-controller communication (see OPC UA over TSN).
- Security: Messages can be signed and encrypted using keys from a Security Key Service, since publishers and subscribers don't open sessions with each other.
- Documentation: The documentation team documents published data sets, their encoding (UADP or JSON), transport, publishing interval and security configuration.
OPC UA PubSub vs. MQTT
MQTT is a transport protocol with arbitrary payloads. OPC UA PubSub defines what the messages contain and how they relate to an OPC UA information model; it can use MQTT as its transport.