[OASIS Issue Tracker] (MQTT-471) Topic Alias and QoS 0

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

    [ https://issues.oasis-open.org/browse/MQTT-471?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=66658#comment-66658 ] 

Ken Borgendale commented on MQTT-471:
-------------------------------------

The receiver is allowed to throw away a QoS 0 message, but must process the packet containing it.  Since the transport is known to be reliable, if the topic alias was set in a previous packet, then it is set.

I do not see any issue here.

> Topic Alias and QoS 0
> ---------------------
>
>                 Key: MQTT-471
>                 URL: https://issues.oasis-open.org/browse/MQTT-471
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Bug
>          Components: edits
>    Affects Versions: 5, wd14
>            Reporter: Konstantin Dotchkoff
>            Priority: Minor
>             Fix For: 5, wd14
>
>
> This issue was originally reported in MQTT-417, but doesn't seem to be addressed in WD14. 
> Lines 1860-1862
> "If a Topic Alias mapping has been set at the receiver, a sender can send a PUBLISH packet that contains that Topic Alias and a zero length Topic Name. The receiver then treats the incoming PUBLISH as if it had contained the Topic Name of the Topic Alias."
> How does the sender knows whether a topic alias mapping has been set at the receiver if the message is QoS 0?



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