Re: [sipcore] Fwd: New Version Notification for draft-sparks-sipcore-refer-clarifications-03.txt

Adam Roach <adam@nostrum.com> Wed, 13 August 2014 15:27 UTC

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Date: Wed, 13 Aug 2014 10:26:59 -0500
From: Adam Roach <adam@nostrum.com>
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To: Ivo Sedlacek <ivo.sedlacek@ericsson.com>, Robert Sparks <rjsparks@nostrum.com>, Andrew Allen <aallen@blackberry.com>, "sipcore@ietf.org" <sipcore@ietf.org>
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Subject: Re: [sipcore] Fwd: New Version Notification for draft-sparks-sipcore-refer-clarifications-03.txt
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On 8/13/14 10:03, Ivo Sedlacek wrote:
> RFC6665, section 4.5.1, 1st sentence states:
>
> 	Notifiers MUST implement the Globally Routable User Agent URI (GRUU) extension defined in [RFC5627], and MUST use a GRUU as their local target.
>
> Isn't notifier a role taken in subscription, applicable only for the dialog of the subscription?
> The UA does not act as notifier in the dialogs created by the particular INVITE request.
> Thus, in my reading, the requirement does not apply for the particular INVITE request.
> Or do I miss anything?

This is exactly what the document that I'll be producing is going to 
clarify.

For what it's worth, "notifier" is defined in section 2 of 6665, and 
it's not a role.

To the point of the specific section you quote, let's look at the whole 
paragraph:

    Notifiers MUST implement the Globally Routable User Agent URI (GRUU)
    extension defined in [RFC5627], and MUST use a GRUU as their local
    target.  This allows subscribers to explicitly target desired
    devices.

Now, take a moment to think really hard about what the second sentence 
there means. If it's not nonsense or useless noise -- and I assure you 
that it is not -- then it must be referring to the ability to subscribe 
to something on a device that the subscriber already knows exists. In 
order to make that happen, the subscriber must have learned the GRUU 
some way.

How do subscribers learn about GRUUs? It's right there in the first 
sentence: Notifiers include GRUUs as their local target. We'll come back 
to this.

The use cases that make this interesting are those that involve 
subscribing to some information about a dialog that you're already in 
(or were recently in). In fact, not just *any* dialog, but INVITE 
dialogs. So how does this happen?

As I said above: notifers include GRUUs them as their local target. 
Every time. Including INVITE dialogs.

/a