Understanding the MQTT puzzle -- clients, servers, and connections

The MQTT broker is known as MQTT server in MQTT 3.1.1, and therefore, we will refer to it as the server. However, we must take into account that the documentation for MQTT servers, tools and client libraries can use the old MQTT broker name to refer to the server.

The MQTT server uses the previously explained topic-based filtering to filter and distribute messages to the appropriate subscribers. There are many MQTT server implementations that provide additional message filtering features by providing custom plug-ins. However, we will focus on the features that are part of the MQTT requirements.

As previously explained, in MQTT the publishers and the subscribers are completely decoupled. ...

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