Exploring MQTT features

In this section, we will have a closer look at some important features of MQTT:

• QoS: For message buffering (when offline).
• Last will/testament: To let the network know when a device goes offline; for example, due to empty batteries.
• Keep alive: To define how often each device needs to call back home to let the MQTT server know that it is still online.
• Persistent sessions: To store various information on the MQTT server, while the client is offline.
• Retained messages: To keep messages available for new subscribers.

Quality of Service

MQTT supports a feature called QoS, which makes it possible for clients to receive messages that were sent while the device was offline. You can see this feature being used in...