====
MQTT
====

.. contents:: :local:


Quick definition
================

   MQTT is one of the most popular protocol when it comes to IoT and communications between nodes. It is based on the principe of publisher - subscriber.
   A broker, which can be seen as a server, is responsible to route all messages from a publisher to all registered subscribers.
   It provides advanced functions like a last will and testament options, as well as 3 different quality of service levels.


Description
===========

   A MQTT system is composed at least of 3 nodes so that it is useful (well, a broker alone or a broker + publisher or even a broker + subscriber would definitely work, but it won't really useful...) :

      1. Broker : kind of the server, routes messages from publisher to subscriber(s), manages quality of services, ...
      2. Clients :

         a. publisher : typically a sensor, publishes data most likely formatted as a JSON string on a topic.
         b. subscriber : get all messages of the topic(s) it is subscribed to, typically a node on the cloud that will store data in a database.

   The topics are kind of communication channels that each client can subscribe to.

   .. figure:: img/mqtt_overview.*
      :align: center
      :alt: MQTT overview,
      :width: 500px

      MQTT communication, source : https://www.eclipse.org/community/eclipse_newsletter/2014/october/article2.php

Examples
========

   Find an example of a broker and clients for Linux in :doc:`Linux, MQTT </tools/linux/mqtt>`

   For client examples in python, see :doc:`Python, MQTT </languages/python/mqtt>`

:tag:`Protocols`
:tag:`MQTT`
:tag:`Python`