MQTT stands for Message Queuing Telemetry Transport. It is an extremely lightweight messaging protocol based on the publish and subscribe pattern. As with any message queuing model, it is an asynchronous protocol.

As shown in the following diagram, publish and subscribe (pub/sub) models rely on three actors:

The three actors are explained as follows:

• The publisher is the actor that produces any content and publishes it to a given subject (known as a topic).
• The subscriber is an event consumer. The subscriber subscribes to its subjects (topics) of interest and gets the event published every time a publisher creates a publication to one of its subscriptions.
• The Broker is responsible for receiving publications and notifying the subscribers of a topic of interest.

Now let's move on to the next important technical element.