MQTT is a communication protocol tailored for IoT based on the publish-subscribe mechanism.

It usually defaults to port 1883.

To use MQTT, one requires a MQTT broker and MQTT publishers / subscribers. ossia score can both publish and subscribe to MQTT topics.

Note that MQTT does not have a concept of automatic discovery: instead, one must use the “Learn” feature to discover available MQTT topics, or create one manually just like in OSC devices.

Example

To try MQTT, one can use Mosquitto.

In a terminal, start the MQTT broker with:

$ mosquitto

In a second terminal, publish a message hi to a topic /foo:

$ mosquitto_pub -t /foo -m hi --repeat 1000000 --repeat-delay 1 -h 127.0.0.1

In a third terminal, listen to the messages sent to the topic /bar:

$ mosquitto_sub -t /bar

In ossia, connect to 127.0.0.1 with the MQTT protocol, use the “Learn” feature to discover /foo, and add a new child node to send messages to the /bar topic.

Important : many MQTT brokers are unable to handle loops, that is, one cannot both publish and subscribe to the same topic as is customary with e.g. OSC.