Subject: RE: 183, BCP & forking

From: "Schroeder, Tim" <[email-masked]>
Date: Mon, 22 Nov 1999 16:38:30 -0600

Gonzalo,

Gonzalo Camarillo [mailto:[email-masked]] writes
> The problem is not when we callee (B-party) is a "black phone". The
> problem I see is when the caller (A-party) is one PSTN-like phone.

> So, A is calling B, and B can be reachable at B1, B2 and B3.

> B1 sends back a 183, and A hears from the speaker some kind of announce.
> In the meantime, B picks up B2, and A receives a 200. Now A's speaker
> suddently stops playing the message from B1, tears down the connection
> with B1 and connects to B2... then we will CANCEL the other branches, so
> as soon as we receive the first 200 there is no problem with receiving
> subsequent 200 responses.

> I believe this is not acceptable.

This behavior seems to happen a fair amount even today.  I call a call
center, and get some ringback.  Shortly thereafter I hear an announcement
about how all representatives are busy, then get switched to music for a
bit.  At some point the music is interrupted for another announcement (or
even an advertisement).  Eventually (hopefully) either the announcement or
the music is interrupted by a human answering the phone, possibly preceded
by another bit of ringback.

Or I call someone's home, and get the start of an answering machine message,
but then a live person picks up the phone, interrupting the answering
machine (which hopefully has enough smarts to shut itself off at that
point).

> What do you suggest if we receive two 183 responses from different
> locations? Which one shall the caller hear?

I think that would be up to the UAC, right?  If my equipment is somehow
capable of doing both, maybe I can receive both.  If my equipment is a
"black phone", maybe I hear neither, but just hear some locally-generated
ringback.  (I know that's not the intent of the 183 Session Progress, but
this afternoon I'm having some problem with the one-way media path set up in
the 183 message.)

Tim Schroeder

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---

From: Gonzalo Camarillo <[email-masked]>
Date: Tue, 23 Nov 1999 15:44:50 +0200

Tim,

> by another bit of ringback.

Here I do not see the problem, since all these announcements are
coordinated by the same call center.

> machine (which hopefully has enough smarts to shut itself off at that

Well, this is a diferent story, since the answering machine has to be
the last location to be tried (not in parallel with the rest). If we
perform parallel searches and the answering machine is tried at the same
time as my mobile I will probably get lots of voice mails and not that
many calls :o)

If can take a look at the mailing list archive there was a proposal from
Ericsson some time ago about adding a new 2xx SIP response. It would be
280, meaning "the call has been connected to a voice mail/answering
machine". This way, when trying to reach the user, this location is not
taken into account when the response arrives.

By the way, what happened with this proposal?

Regards,

Gonzalo
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