MQTT Stands for

Message Queueing Telemetry Transport and it is a connectivity protocol on top of TCP/IP designed for Internet of Things (IoT) devices. 

A server that receives all messages from the clients and routes these messages to the appropriate destination.

And MQTT broker is..

The QoS defines how hard the Broker or Client will try to ensure that the message is received.

Quality of Service (QoS)

Higher level of QoS are more reliable, but involve higher latency and have higher bandwidth requirement

QoS (continued)



A retained message is a normal MQTT message with the retained flag set to true. 

Retain Message (continued)

The broker will keep the retain message even after sending it to all current subscribers.

Retain Messages (continued)

That makes sense when you want newly-connected subscribers to receive messages immediately

In MQTT, you can use the Last Will and Testament (LWT) feature to notify the other clients about an ungracefully disconnected client.

What is LWT?

The broker stores the message until it detects that the client has disconnected ungracefully.

LWT  (continued)

Swipe for more info