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Subject: Re: [mqtt-comment] MQTT 5.0 WD13 - No Local subscription option


1. I will fix the missing "Subscription".

2. The semantics of a shared subscription are that the message is sent to one of the subscribers and we do not define how the server decides which to send it to. The various subscribers all have a ClientID so the message would be local to at most one of them. If the server decided to deliver the message to the one which is local (publisher and subscriber have the same ClientID), then the message would not be sent to anybody which seems undesirable. The alternative is to define rules for how the server allocates messages to subscribers. This is also undesirable. Therefore we went with the same solution used by other protocols such as JMS which is simply to not allow noLocal and shared subscriptions to be used together.


Ken Borgendale -- kwb@us.ibm.com


<mqtt-comment@lists.oasis-open.org> wrote on 05/30/2017 12:22:00 PM:

> From: Boris Verkhovykh <b_a_v@mail.ru>

> To: mqtt-comment <mqtt-comment@lists.oasis-open.org>
> Date: 05/30/2017 12:22 PM
> Subject: [mqtt-comment] MQTT 5.0 WD13 - No Local subscription option
> Sent by: <mqtt-comment@lists.oasis-open.org>
>
> Hello!
>
> Please consider the following paragraph:
>
> 2332 3.8.3.1 Subscription Options
> ...
> 2337 Bit 2 of the Subscription Options represents the No Local option. If the value is
> 1, Application Messages
> 2338 MUST NOT be forwarded to a connection with a ClientId equal to the ClientId of the publishing
> 2339 connection [MQTT-3.8.3-3]. It is a Protocol Error to set the No Local bit to 1 on a
> Shared [MQTT-3.8.3-4].

> I guess, the word "Subscription" is missed at the end.
>
> Second, what is the rationale to prohibit the "No Local" option for Shared Subscriptions?
> I would see a useful scenario: client asks to pass a message to one of its peers (if
> they exist), while accepting similar messages from others.
> It may help building auto-configurable systems.
>
> Best regards,
>
> Boris Verkhovykh



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