MQTT version support

The Amlen Bridge supports MQTTv3.1(eclipse), MQTTv3.1.1 (OASIS), and MQTTv5.0 (OASIS). MQTTv3.1.1 is also standardized as ISO/IEC 20922:2016.

A number of functions that are used by the Bridge are only available in MQTTv5.0. These functions include error reporting, message properties, subscription options, and session expiry. The Bridge works with MQTTv3.1.1 server but these functions are not available.

MQTTv3.1 does not support session existence detection, so problems might be encountered if using cleansession=false for durable session connections.

The Bridge is primarily tested with Eclipse Amlen, and IBM Watson™ IoT Platform messaging, but can work with any other servers implementing these versions of MQTT.