Two offer/answer cycles during session setup

Hi,

I would like to use two offer/answer cycles during session
setup (without
using UPDATE) and ask for feedback if the following sequence
will work.

This is the sequence seen from UAC perspective.

UAC                               Proxy
--- INVITE  SDP-1 ------------------>
<-- 183 Session Progress  SDP-2 -----

<-- 200 OK SDP-3 --------------------
--- ACK SDP-4 ---------------------->

The point is that 200 OK carries a new SDP (SDP-3, the
actual SDP of the
Session Partner), while 183 carries the SDP-2 of an
announcement.

SDP-1 / SDP-2 is the first offer/answer
SDP-3 / SDP-4 is the second offer/answer (expectation SDP-4
= SDP-1).

>From my interpretation of RFC3264 the sequence could
work. The Caller gets a
special announcement before cut through.

My doubts & questions are now:
- Will UACs follow the change of SDP during session setup?
- Will SDP-4 be identical to SDP-1?

Who knows how UAs might behave?

Cheers
Franz

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Hi Franz,

I think only one answer can answer your both questions, that
is UAC can
decide whether accept your new offer(SDP-3)

So,
1)Will UACs follow the change of SDP during session setup?
if UAC want to accept your SDP-3, it will follow the change
of SDP,
otherwise it will not.

2)Will SDP-4 be identical to SDP-1
if UAC don't accept your SDP-3, SDP-4 may be indentical to
SDP-1



On 1/25/07, Franz Edler <franz.edlerinode.at> wrote:
>
> Hi,
>
> I would like to use two offer/answer cycles during
session setup (without
> using UPDATE) and ask for feedback if the following
sequence will work.
>
> This is the sequence seen from UAC perspective.
>
> UAC                               Proxy
> --- INVITE  SDP-1 ------------------>
> <-- 183 Session Progress  SDP-2 -----
>
> <-- 200 OK SDP-3 --------------------
> --- ACK SDP-4 ---------------------->
>
> The point is that 200 OK carries a new SDP (SDP-3, the
actual SDP of the
> Session Partner), while 183 carries the SDP-2 of an
announcement.
>
> SDP-1 / SDP-2 is the first offer/answer
> SDP-3 / SDP-4 is the second offer/answer (expectation
SDP-4 = SDP-1).
>
> >From my interpretation of RFC3264 the sequence
could work. The Caller
> gets a
> special announcement before cut through.
>
> My doubts & questions are now:
> - Will UACs follow the change of SDP during session
setup?
> - Will SDP-4 be identical to SDP-1?
>
> Who knows how UAs might behave?
>
> Cheers
> Franz
>
> _______________________________________________
> Sip-implementors mailing list
> Sip-implementorscs.columbia.edu
> https://lists.cs.columbia.edu/cucslists/listinf
o/sip-implementors
>
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