MQTT

• Largely used on IoT devices

• Pub-sub mechanism

• Mostly run on TCP/IP

• Requires a broker to route messages in topics

• Lightweight

• For resource-constraint clients and low-bandwidth environments

If the connection from a subscribing client to a broker is broken, then the broker will buffer messages and push them out to the subscriber when it is back online.

Quality of Service (QoS)

At most once (0) – the message is sent only once and the client and broker take no additional steps to acknowledge delivery (fire and forget). At least once (1) – the message is re-tried by the sender multiple times until acknowledgement is received (acknowledged delivery). Exactly once (2) – the sender and receiver engage in a two-level handshake to ensure only one copy of the message is received (assured delivery).

How lightweight is MQTT?

• 2 bytes of fixed header

• A message payload up to 256MB that contains data and QoS

Other pros over HTTP

• An MQTT connection can be reused multiple times, so it has less overhead to construct request packet than HTTP

Source

• https://internetofthingsagenda.techtarget.com/definition/MQTT-MQ-Telemetry-Transport#:~:text=MQTT is considered a lightweight,of service (QoS) level.

• https://stackoverflow.com/questions/31502569/why-mqtt-is-called-as-light-weight-messaging-protocol

• https://mqtt.org/

• https://en.wikipedia.org/wiki/MQTT