[OASIS Issue Tracker] Updated: (MQTT-156) Vague treatment of "at most once"

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

     [ http://tools.oasis-open.org/issues/browse/MQTT-156?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Richard Coppen updated MQTT-156:
--------------------------------

    Proposal: 
Modify normative statement [MQTT-3.8.4-6] to make 'at most once' to mean 'at most once' under Section 3.8.4

Remove >>The server is permitted to send duplicate copies of a message to a subscriber in the case where the original message was published with QoS 1 and the maximum QoS granted was QoS 0.[MQTT-3.8.4-6] <<

Replace with:

To avoid the risk of duplicate messages being published to QoS 0 subscribers, the Server MUST NOT forward a message to a QoS 0 subscriber if the message arrived with QoS 1 and the duplicate flag was set to 1. [MQTT-3.8.4-6]

Remove the following sentence in the non-normative comments (line 1213 in CSD):

"A QoS 1 Message published to the same topic might either get lost or duplicated on its transmission to that Client."

  was:
Modify normative statement [MQTT-3.8.4-6] to make 'at most once' to mean 'at most once'

Remove >>The server is permitted to send duplicate copies of a message to a subscriber in the case where the original message was published with QoS 1 and the maximum QoS granted was QoS 0.[MQTT-3.8.4-6] <<

Replace with:

To avoid the risk of duplicate messages being published to QoS 0 subscribers, the Server MUST NOT forward a message to a QoS 0 subscriber if  the  message arrived with QoS 1 and the duplicate flag was set to 1. [MQTT-3.8.4-6]      


> Vague treatment of "at most once"
> ---------------------------------
>
>                 Key: MQTT-156
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-156
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 3.1.1
>         Environment: Technical
>            Reporter: Patrick Durusau
>             Fix For: 3.1.1
>
>
> In 4.3.1 4.3.1 QoS 0: At most once delivery:
> "The message arrives at the receiver either once or not at all."
> At most once delivery raises expectations about making sure no message is delivered twice.
> It is unclear how duplicates of a messages are prevented from "arriving". What mechanism allows for that QoS aspect? (i.e. duplicate elimination). If there is no explicit provision for eliminating duplicates, aren't we rather talking of more simply "Best effort" semantics?

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