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Subject: [OASIS Issue Tracker] Commented: (MQTT-68) Message delivery retry is not required where no network failure is detected

    [ http://tools.oasis-open.org/issues/browse/MQTT-68?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=34802#action_34802 ] 

Peter Niblett commented on MQTT-68:

Change the proposal to say

Remove existing content in this section and replace with:

When a Client reconnects with CleanSession = 0, both the client and server MUST redeliver any previous in-flight messages. This means re-sending any unacknowledged PUBLISH  packets (where QoS > 0) and PUBREL packets. This is the only circumstance where a Client or Server is REQUIRED to redeliver messages. Clients MAY resend SUBSCRIBE and UNSUBSCRIBE packets on reconnect but are not REQUIRED to do this.

While a modern TCP network is unlikely to lose packets, a Client or Server is permitted to attempt redelivery at other times. However, redelivery is not encouraged unless a network failure has been detected.

Non-normative comment

Historically retransmission of Control Packets was required to overcome data loss on some older TCP networks. This might remain a concern where MQTT 3.1.1 implementations are to be deployed in such environments.

> Message delivery retry is not required where no network failure is detected 
> ----------------------------------------------------------------------------
>                 Key: MQTT-68
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-68
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 3.1.1
>            Reporter: Richard Coppen
>             Fix For: 3.1.1
> WD08 (section 4.3) states that if no response is received from PUBLISH, PUBREL, SUBSCRIBE, UNSUBSCRIBE within a reasonable period of time then the sender may retry delivery. 
> This attempts to cater for unreliable TCP/IP networks. Since modern compliant TCP/IP networks should not lose packets, then the sender should not retry unless a network failure is detected.
> The spec should be changed to reflect this and add non-normative content to describe the historical problem.  

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