MQTT Broker

The central server in an MQTT pub/sub system. All messages pass through the broker.

Broker functions:

1. Accepts messages from publisher clients
2. Stores retained messages (one per topic)
3. Manages subscriptions (subscribe/unsubscribe requests)
4. Forwards messages to subscribed clients
5. Handles persistent sessions (stores missed messages for QoS 1/2)
6. Sends Last Will & Testament on unexpected client disconnect

Brokers can be public (test.mosquitto.org) or private. Azure IoT Hub acts as a managed MQTT broker.

See Also

• MQTT and IoT Protocols topic
• Sub concept, QoS concept