MQTT (Message Queuing Telemetry Transport)

• MQTT is a M2M (Machine-To-Machine) connectivity protocol.
• MQTT is based on Publisher/Subscriber model.
• It was created to connect to the systems situated in remote place and to get data from those sensor.
• Decoupling can be done because of Publisher/Subscriber model which is hard to achieve in Client/Server model.

MQTT Components

MQTT has 3 basic components

• Publisher (e.g. Motor, Mobile Devices, etc.)
• Subscriber (e.g. Temperature sensor, Motion Sensor, etc.)
• Broker

MQTT Publisher

• System or sensors which collects data and send it to the broker which further sends it to multiple subscribers.
• Example motion sensor, water level sensor, etc.
• Publisher publish data in following formats
  • Binary
  • JSON
  • SDC Record
  • Text

MQTT Subscriber

• Subscriber can be a mobile device, data server, monitoring stations, etc. which receives publish data from broker so that it can act according to it or monitor it or store it.
• Subscriber send request to broker to send required publisher’s data.
• Broker has the table in which it maintains all subscriptions request, and send publish data according to it.
• Example Mobile devices, Monitoring system, etc.

MQTT Broker

• Broker is the component which take care of receiving data from Publisher and sending it to Subscriber accordingly.
• Broker has to filter messages, broker can filter messages in following ways.
  • Subject based
  • Content based
  • Type based
• Broker has a subscription table in which it store all the request from the subscriber for the publisher’s data.
• Broker sends publish data to multiple subscriber according to this list.

Decoupling in Pub/Sub

• Space decoupling:- In MQTT there no need for publisher and subscriber to know each other, since it is Pub/Sub model there no need to exchange IP address.
• Time decoupling:- Since it is Pub/Sub model there is no need for publisher and subscriber to run on same time.
• Synchronization decoupling:- Operations on both publisher and subscriber do not need to be interrupt during the publishing and receiving.