Subject: Re: [Sip] solving early media, HERFP, and unifying manyfolks

From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 31 Jan 2002 23:42:54 -0500

Sanjoy Sen wrote:

> > There is no difference between early media and media. Local alerting
> > would presumably take place as a local implementation choice once a
> > suitable provisional response (180, typically) has been received to
> > indicate that the far end is, in fact, ringing. It would
> > continue until
> > the establishment of the session, early or otherwise. As a
> > result, a 183
> > w/SDP finalizes the establishment of the session, and so that
> > would stop
> > any local ringback.
> >
> > I suppose that suspension of the session, with port zero, before the
> > dialog is completed, would be a way to signal a UAC to revert back to
> > local ringback, if that functionality was needed.
> 
> Yes, but there would a problem with general PSTN interworking. When the
> MGC receives an ACM/Alerting message, it has no way to definitively
> infer whether the PSTN would generate early media (e.g., remote
> Ring-back or announcement). So, on receipt of ACM, the MGC may send an
> 180 (as you said) to the SIP phone which starts playing local ringing
> (by local implementation choice), but then any early media which might
> be coming through the gateway will be lost (the EM flow can start
> anytime after the ACM is issued). I was wondering what kind of rules do
> we need to specify to solve this issue and whether its at all solvable
> by rules alone.

I don't get the problem. Once the gateway receives media, it can
establish the session by sending an offer in an UPDATE. 

Also, I thought there was some bit somewhere in the ACM which indicated
that ringback was inband...

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
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---

From: [email-masked]
Date: Fri, 1 Feb 2002 11:27:54 +0530

Backwards Call Indicator (BCI) parameter of the ACM indicates
   that interworking has been encountered (generally designating that
   the ISUP network sending the ACM is interworking with a less
   sophisticated network which cannot support cause codes), then there
   may be in-band announcements of call status such as an audible busy
   tone or caller intercept message.

rgds
Sumit
Hughes Software Systems

Jonathan Rosenberg <[email-masked]> on 02/01/2002 10:12:54 AM

To:   Sanjoy Sen <[email-masked]>
cc:   [email-masked] (bcc: Sumit Dhar/HSSBLR)

Subject:  Re: [Sip] solving early media, HERFP, and unifying manyfolks

Sanjoy Sen wrote:

-Jonathan R.

---

From: [email-masked]
Date: Fri, 1 Feb 2002 12:43:00 +0530

Hi ,

The inband information indicator in OBCI (optional backward call indicator) of
ACM indicates that
the inband information is present from SCN. Based on this information the
gateway switches the reverse media
path and sends the early media answer sdp in 183 and the announcements will be
played in the sip terminal.
Otherwise the gateway is going to respond with 180  and the local rbt  will be
applied in the SIP terminal.

Rgds,
-Elias

[email-masked] on 02/01/2002 11:27:54 AM

To:   Jonathan Rosenberg <[email-masked]>
cc:   Sanjoy Sen <[email-masked]>, [email-masked] (bcc: Mohamed Ibrahim
      Elias/HSS)

rgds
Sumit
Hughes Software Systems

Sanjoy Sen wrote:

-Jonathan R.