What Is OPC UA Pub/Sub?

The Founder's Explanation (Teach Exactly This Way)

"To tell one thing to a whole town, you do not phone each person one by one. You print it in the newspaper or say it on the radio — once — and everyone who wants, reads or listens. That is publish and subscribe. OPC UA Pub/Sub lets one source announce data once, and any number of listeners receive it, without a separate call to each."

Teaching the Concept

The Newspaper, Not the Phone Call To reach a whole town, you do not phone everyone — you print it once in the newspaper, and all who wish to, read it. OPC UA Pub/Sub is that newspaper: publish once, and any number of subscribers receive it, without a call to each. It scales where a call-per-listener cannot. The Model ``` PUBLISHER emits data messages (no per-client session) SUBSCRIBERS any number, receive independently TRANSPORT BROKERED via MQTT BROKER-LESS via UDP multicast decoupled: producer does not know the consumers ``` Choosing the Transport ``` MQTT broker cloud / wide-area, store-and-forward UDP broker-less local, lowest latency, real-time control ``` Pub/Sub turns one source into a broadcast — publish once, and any number of consumers listen, at scale.

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Related Topics

• MQTT for IoT in buildings — lightweight publish-subscribe telemetry
• What is OPC UA in BMS and when is it needed? — when to reach for OPC UA
• Browse all Protocols topics — more from this section of the EnSmart BMS Library