Subject: WG: [Sipping] Comments on draft-elwell-sipping-qsig2sip

From: "Alexeitsev, D" <[email-masked]>
Date: Wed, 29 May 2002 14:07:51 +0200

Thank you for the response!

Some comments inline

Greetings
Denis Alexeitsev

-----Ursprüngliche Nachricht-----
Von: Peterson, Jon [mailto:[email-masked]]
Gesendet am: Mittwoch, 29. Mai 2002 12:30
An: 'Alexeitsev, D'; [email-masked]
Cc: [email-masked]
Betreff: RE: [Sipping] Comments on draft-elwell-sipping-qsig2sip

This note in 3.3 only suggests that before a SAM arrives at a gateway in an
overlap dialing scenario, a response could be received for the initial
INVITE transaction (the one corresponding to the original IAM received by
the gateway). Since presumably the call cannot be answered (because the
address is incomplete), this INVITE could only receive a provisional (1xx)
response, not a success (2xX) response. 

It is however possible to establish an early dialog (see RFC3261 section
12.1) with a 1xx response - the 1xx can contain a Contact header, To tags,
i.e. the required protocol apparatus for a dialog. This note merely says
that if you happen to receive such a response in time, you shouldn't use
that Contact header, those To tags, and so on in any INVITE you will send
based on a SAM, since this would force requests to go to the same
destination. Since there is no guarantee either way that you will receive an
usable 1xx response in time to send a second INVITE after a SAM arrives, it
would be tough to rely on this behavior if you were, for whatever reason,
interested in forcing requests to go to the same destination.

[DA]Could this early dialog establishment option be somehow reflected in the Note to the section 3.3

Then again, if you're only interested in sending requests to the same
destination, that would seem to miss the point of collecting more address
digits from SAMs in the first place, since presumably the dialed number
tells you how to direct the call (and the originating gateway will most
likely have no idea whether the destination is a gateway or not). 

[DA] If I-GW got the 112233 so far in the IAM and it is not enough to route the call, then it can not send the initial INVITE anyway. But if this digits are enough to route the call to the O-GW1 I do not expect, that if the I-GW gets the 44 in the subsequent SAMs the call will be re-routed to the O-GW2. Anyway this is the network design question.

To be clear, speaking to the note that kicked off this thread, section 3.7 of the
overlap draft does not recommend any practices that sacrifice services in
order to route calls to the same gateway - quite the contrary. The
conclusion to that section reads:

   If sending multiple IAMs to the PSTN is not
   acceptable in a particular domain, overlap signalling should not be
   used.

Jon Peterson
NeuStar, Inc.

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