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Subject: [OASIS Issue Tracker] (MQTT-276) MQTT enhancements for large scale distributed systems

    [ https://issues.oasis-open.org/browse/MQTT-276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=61636#comment-61636 ] 

Ken Borgendale commented on MQTT-276:

There are quite a number of constraints that the server might be able to advertise at CONNACK.  For instance:
- What QoS are supported (which might not be max QoS)
- Whether cleansession=0 is supported
- Support for retain
- Max message size
- Max number of subscriptions
- Max publish rate (messages, bytes)
Many of these things are potentially dynamic based on the information in the CONNECT packet (For instance retain is only allowed for some clients).

For a few of the constraints such as max clientID, userid, and password length CONNACK is too late.  

In the presentation, one of the uses of the server initiated disconnect is to inform the client that multiple clients are using a ClientID.  This is indeed a good thing, and is the reason for MQTT-278 (server initiated ping) as the server needs a way of differentiating between a client which reconnects and one which connects twice.

> MQTT enhancements for large scale distributed systems
> -----------------------------------------------------
>                 Key: MQTT-276
>                 URL: https://issues.oasis-open.org/browse/MQTT-276
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: New Feature
>          Components: futures
>    Affects Versions: 3.1.1
>            Reporter: Konstantin Dotchkoff
>            Assignee: Konstantin Dotchkoff
>             Fix For: 3.1.1
> As presented during the TC call on 8/6/2015, there are challenges in implementing MQTT in large scale distributed systems with the specific case being QoS 2:
> https://www.oasis-open.org/apps/org/workgroup/mqtt/download.php/56237/MQTT%20QoS2%20Considerations.pptx
> Retained messages were also noted during the call. 

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