[OASIS Issue Tracker] (MQTT-313) MQTT 5.0 WD07 CONNACK code Incompatible with MQTT 3.1 and MQTT 3.1.1

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

Ed Briggs created MQTT-313:
------------------------------

             Summary: MQTT 5.0 WD07 CONNACK code Incompatible with MQTT 3.1 and MQTT 3.1.1
                 Key: MQTT-313
                 URL: https://issues.oasis-open.org/browse/MQTT-313
             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
          Issue Type: Bug
          Components: core
    Affects Versions: 5
            Reporter: Ed Briggs
            Assignee: Ed Briggs


The interoperability of CONNACK(unsupported protocol level) between MQTT 5.0 WD07 and MQTT 3.1.1 and MQTT 3.1 seems to be broken. My questions are 'is this a defect' and 'should it be changed'.

MQTT 5.0 WD07 uses a different CONNACK return code for this condition as summarized  be low

Ver           retval                                    retval
                 0x01                                    0x84
3.1            unsupported prot. level       UNDEFINED-RESERVED
3.1.1         unsupported prot. level       UNDEFINED-RESERVED
5.0 WD07  UNDEFINED-RESERVED   unsupported protocol level


As a consequence, the following useful exchanges no longer work


3.1 or 3.1.1 Client           5.0 WD07 Server
    CONNECT 3.1       ->     
                                   <-    CONNACK 0x84
    UNSPECIFIED 

                    - - - 

3.1 or 3.1.1 Client           5.0 WD07 Server
    CONNECT 3.1.1    ->     
                                   <-    CONNACK 0x84
    UNSPECIFIED 


5.0 WD07 Client                 MQTT 3.1 or 3.1.1 Server
     CONNECT 5.0      ->
                                   <-    CONNACK 1
     UNSPECIFIED 

Comments

I submit interoperability is necessary in this ONE particular case.



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