Subject: [Sipping] Question on pstn-call-flows-02 draft

From: "Hearty, John" <[email-masked]>
Date: Thu, 10 Jul 2003 09:34:25 -0600

In section 2.2 message F7-F8, why is a 180 sent when the Progress
indicator shows further call progress information may be available
in-band?  It would seem to me that for sure if it was 8 (In-band info or
appropriate pattern now available), and probably 1, a 183 should be
returned.

Somewhat related to this I'd like some input on another flow not
documented.  For an IP to PSTN flow where the caller does not send SDP
in Invite (offer in 200, answer in ACK), we have no way to forward
in-band progress tones/announcements.  What is the best SIP response to
send in this case when a PSTN backwards message indicates progress
tones/announcements may be available in-band?  With a 180, the caller
may falsely believe the call is ringing when it could be going to an
announcement.  183 won't serve much purpose since the gateway doesn't
yet know the caller's address to send RTP to, presumably the caller
would get silence.  Sending no provisional beyond 100 is another option,
also resulting in silence.  Any opinions what is best?

John Hearty
Level3

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