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Subject: [OASIS Issue Tracker] (MQTT-257) Flow Control


    [ https://issues.oasis-open.org/browse/MQTT-257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=59239#comment-59239 ] 

Raphael Cohen commented on MQTT-257:
------------------------------------

Having talked to Richard, I think there are a couple of possibilities:-

- Having a PAUSE / UNPAUSE packet, a la ethernet. The reality is that this sort of approach just delays the problem, as messages build up at the sender. If a receiver can't cope with volume, it can't cope. At some point, some sort of quota is going to have to kick in and messages need to be rejected. Negative ACKs would allow this.
- Adding a 'max inflight window' value to the CONNECT packet. This would only resolve some of the problem for QoS 1 and QoS 2
- Having the broker auto-throttle; this obviously doesn't help the scenario of a publisher => broker

> Flow Control
> ------------
>
>                 Key: MQTT-257
>                 URL: https://issues.oasis-open.org/browse/MQTT-257
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Bug
>          Components: futures
>            Reporter: Peter Niblett
>
> Developers sometimes ask if there's a way to slow down an MQTT message sender to stop it sending PUBLISH packets faster than the receiver (be it a server or client) is able to process them.
> The receiver can apply back pressure at the TCP/IP level (if it's a TCP/IP transport) or - for QOS 1 and QOS2 - it can delay sending acks so that eventually the sender's inflight message window will fill up, but these mechanisms are a bit crude, and the receiver has no in-band way of letting the sender know what rate is acceptable to it. 
> We need to decide whether this is a problem that affects a significant number of existing or envisaged real-life applications (as opposed to performance and stress tests)



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