[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>]

    [ https://issues.oasis-open.org/browse/MQTT-313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=63754#comment-63754 ] 

Ken Borgendale commented on MQTT-313:
-------------------------------------

I do not understand the issue.  We did recognize that in changing the Connect Return Code values we create some extra work for a client which supports multiple version of the spec.  If the client only supports one version of the spec, there is very little it can do if it receives a return code of Unsupported version regardless of what the encoding of that return code is.   

If a client supports both V3.1.1 and V5 then it should understand both return codes and from that be able to determine its retry with an alternate version.

In reality, most servers will not respond with this return code at all as they will consider a CONNECT with a version they do not support as malformed as they cannot extract the authentication information.




> 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.



--
This message was sent by Atlassian JIRA
(v6.2.2#6258)