[OASIS Issue Tracker] (MQTT-253) Subscription identification

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    [ https://issues.oasis-open.org/browse/MQTT-253?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=64335#comment-64335 ] 

Ken Borgendale commented on MQTT-253:
-------------------------------------

I understand that this is similar to a statement that the client does not need to remember its subscriptions in the client session state. However, most uses of the subID would in fact require the client to keep this data.  This is a good place to use some non-normative text:   If the client uses subIDs it would normally keep them in the client session state which would allow the client to not reuse a subID. The client is of course allowed to duplicate subIDs, but for most uses of the subID that is not a good thing to do.

I presume the the SubID can only be sent on a PUBLISH from server to client.  Is it a protocol error if the client sends one?

Is zero an allowed SubID?  We might want to have text which specifies that due to the var int encoding the valid range is 1 to 2**28-1.

To Shawn:  The goal here is to make this small enough for implementers to be acceptable.  The client is not required to use this feature.  For the server is means saving a 4 byte integer with each subscription.  Is there something in particular you feel is difficult for the server to implement?

> Subscription identification
> ---------------------------
>
>                 Key: MQTT-253
>                 URL: https://issues.oasis-open.org/browse/MQTT-253
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: New Feature
>          Components: futures
>    Affects Versions: 5
>            Reporter: Andrew Schofield
>            Assignee: Andrew Banks
>            Priority: Minor
>
> Subscribe and unsubscribe operations are performed on topic filters in MQTT 3.1.1. Adding subscription identifiers would enable unambiguous identification of subscriptions.



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