1.1. Changes
The following are the changes between MQTT V3 and MQTT V3.1:
- User name and password can now be sent with a CONNECT packet
- New return codes on CONNACK packets, for security problems
- Clarification that clients are not informed of un-authorized PUBLISH or SUBSCRIBE commands, and that the normal MQTT flow should complete even though the command has not been performed.
- Strings in MQTT now support full UTF-8, instead of just the US-ASCII subset.
The protocol version number passed with CONNECT packets, is unchanged for this revision, and remains as the "3". Existing MQTT V3 server implementations should be able to accept connections from clients that support this revision, as long as they correctly respect the "Remaining Length" field, and therefore ignore the extra security information.
http://public.dhe.ibm.com/software/dw/webservices/ws-mqtt/mqtt-v3r1.html