Re: [martini] Announcement of MARTINI WG last Call on "Registration for Multiple Phone Numbers in the SIP"

Adam Roach <adam@nostrum.com> Sat, 24 July 2010 09:55 UTC

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Date: Sat, 24 Jul 2010 11:56:10 +0200
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Cc: Bernard Aboba <bernard_aboba@hotmail.com>, "martini@ietf.org" <martini@ietf.org>
Subject: Re: [martini] Announcement of MARTINI WG last Call on "Registration for Multiple Phone Numbers in the SIP"
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> --------------------------------------------------------------
>
> Issue-2: How does a SIP-PBX that doesn't have SIP endpoints respond to a SUBSCRIBE to reg-event (say, SIP-PBX supports only analog or H.323 lines)? I assume it should create fake registration data is if the target AOR were registered to a SIP endpoint. Does that need to be stated?

You've described pretty much the correct behavior. I'm not certain we 
need to have a lot of discussion about this, although a one-sentence 
summary (similar to what you've put above) probably has some value.

> --------------------------------------------------------------
>
> Issue-3:
> Section 5.2 says...
>     A further implication of this property is that an individual extension
>     that is implicitly registered may also be explicitly registered using
>     a normal, non-bulk registration (subject to SSP policy).  If such a
>     registration exists, it is refreshed independently of the bulk
>     registration, and is not removed when the bulk registration is
>     removed.
>
> I assume this means that an enterprise user AOR can be bound to two (multiple) contact addresses; one bulk-registered by the PBX, and a second explicitly registered by a SIP endpoint directly hosted by the SSP network.
>
> Section 6 of the draft goes on to say that SUBSCRIBE requests to reg-event are handled just like INVITE requests, which means that if the target AOR has multiple contacts, the SUBSCRIBE request is forked. This seems like a problem, since RFC3680 disallows forking (RFC3680 section 4.9).

Yeah, I've always considered event packages that forbid multiple 
subscriptions in the case of a forked SUBSCRIBE to indicate a lack of 
imagination on behalf of the event package designer. :)

Basically, the only way to make this work properly would be to require 
the SSP to maintain back-end subscriptions to the PBX(es), and to 
compose all the relevant data into a single record. This isn't a 
difficult problem, but it requires significant new code in the SSP. The 
only way we could guarantee this working would be to mandate such 
behavior. I don't think that'll make people particularly happy.

I'll add a slide to the deck for discussion at the face-to-face meeting 
to see what people want to do here.

/a