Concept

What is Message Queuing Telemetry Transport (MQTT)? link

Message Queuing Telemetry Transport (MQTT) is an open network protocol developed for the communication of telemetry data between devices (Machine-to-Machine). Many IoT devices, such as temperature or humidity sensors, send their data to a central broker. This broker allows clients to subscribe to topics and receive the data from the sensors.

Purpose link

Today, there are over 7 billion IoT devices generating data. To collect and process all this data, a protocol is needed. MQTT was developed precisely for this purpose. It allows IoT devices, which often have limited computing power, to send their data to a broker, which can distribute the data for further processing.

Functionality link

MQTT is based on the publish-subscribe model, meaning there are producers that generate data and send it to the broker, and consumers that receive the data from the broker.

%%{
  init: {
    'theme':'dark'
  }
}%%
graph TD
  producer1("Temperature Sensor 1")
  producer2("Temperature Sensor 2")
  producer3("Humidity Sensor 1")
  producer4("Humidity Sensor 2")
  producer5("Light Sensor 1")
  producer6("Light Sensor 2")
  broker(["Broker"])
  consumer("Consumer (Receiver)")

  producer1 ==> broker
  producer2 ==> broker
  producer3 ==> broker
  producer4 ==> broker
  producer5 ==> broker
  producer6 ==> broker
  broker ==> consumer

In MQTT, all messages must always be tagged with a topic. This serves as an identification to clarify the subject of the message. A topic is a string that can consist of multiple levels, separated by the / character. A topic must be at least one character long and is case-sensitive.

Since a consumer can be interested in multiple topics, there are also wildcards that can be used in a topic. These are + and #. The + character replaces exactly one level of the topic, and the # character replaces 0 or more levels of the topic, but the # can only be at the end of the topic.

Resources link

MQTT - Wikipedia
MQTT.org
MQTT 3.1 Spezifikation