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

[ https://issues.oasis-open.org/browse/MQTT-253?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=59238#comment-59238 ] 

Raphael Cohen commented on MQTT-253:
------------------------------------

I like the idea, and would ordinarily be in favour, as it eliminates the ambiguity of overlapping subscriptions, but I think it creates complexities for simpler clients. Here are my observations:-

- How would a client that is automatically subscribed on connection know how to unsubscribe? It wouldn't know the subscription ids
- How would a client that can't persist durable state know on a subsequent connection what its subscription ids are?
- Imagine a simpler C client on an embedded device which uses #define constants for topic filters. It now needs writable flash space to store this state data, and so makes the programmer's job harder

> 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: 3.1.1
>            Reporter: Andrew Schofield
>
> 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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