[SIPForum-techwg] Question re Application Server

[Hadriel Kaplan]

Hey Paul,
Comments inline...

> -----Original Message-----
> From: techwg-bounces at sipforum.org [mailto:techwg-bounces at sipforum.org] On
>
> Then there is the address that is the registration target. It must be an
> address in the domain of the SP. But it would be very bad if it was the
> SP equivalent of one of the enterprise's phone numbers. (E.g.
> sip:++12125551234 at service-provider.net;user=phone) It would be bad
> because once registration is accepted to that it will be *extremely*
> surprising if a request targeted to that address isn't routed to the
> registered contact. (It is *legal* but surprising and misleading.) And
> it would be equally bad if it was a phone number assigned to somebody
> else. So I guess maybe it shouldn't be a phone number at all. Perhaps it
> would be best if it were something like sip:acme.com at service-provider.net.

Not that I disagree with your general point, but why can't acme-pbx register
the AoR 12125551234 at service-provider.net with a contact of
12125551234 at acme.com?  The SP will be getting that registered AoR in
requests from other Enterprises and its PSTN GW for the number, and can set
the req-uri to the contact, and it should work.  The To-uri the PBX receives
won't be what the spec says, but those rules should be relaxed anyway as per
your other email. (or am I missing your example?)
 

> The mechanism of implicit registration sets introduced by IMS blends
> more harmoniously with SIP. (Not that I love the mechanism.) With it,
> you register to one of your AORs, and a bunch of associated ones are
> *implicitly* registered with the same contact. Requests addressed to any
> of those AORs are routed using normal registrar/home proxy methods,
> replacing the R-URI with the registered contact. Because the same
> contact is shared by many AORs, a new P-Called-Party-ID header is added
> that contains the untranslated value of the R-URI. I think that might
> have been a better mechanism to use here, but perhaps it is too late for
> that.

Indeed implicit registration is the mechanism some people use today for PBX
cases that need registration. (not that it's very common for PBX's to
register, mind you)  The only downside with that is the URIs come back in
the P-Associated-URI header and it gets mighty big for reasonable-sized
PBXs.  

-hadriel