[SIPForum-discussion] SDP Body in 183 Progress Message

[Nitin Kapoor]

Sukhbir,

As my understanding says if you are getting SDP in 183 session progress
then normally It will be the same SDP shall be sent in all subsequent
provisional responses - no matter if they are sent reliably or not. You can
only have at most one offer/answer exchange per SIP transaction, so once
you've sent an offer (or answer, if the INVITE did contain an offer) in 18x
you can't send any more within that transaction.

And in the scenario where you have SDP In both the response the UAC normally
will ignore the SDP which is coming in 200 OK.

Also, here as you said if UAC is not sending any SDP parameter in initial
INVITE, then any proxy/b2bua should pass the call after getting some sort of
ACK with  default configuration to UAS, and then UAS will send his media
details in 18x response unidirectional.

Thanks,
Nitin Kapoor

On 16 March 2010 00:41, Sukhbir <threegforum at rediffmail.com> wrote:

> Hi All,
>
> I have one doubt regarding SDP in 183 Progress Message. As i know, SDP in
> 183 progress is used to  play announcent to calling party (UAC). In 183
> Progress with SDP body one can also mention the reason of the inclusion of
> SDP body. Now my question is that if Calling Party (UAC) will receive the
> SDP body in 183 Progress and also later in 200 (Ok) message then what would
> be the behaviour of Calling Party (UAC).
> Should it ignore the SDP given in 200 (Ok) or it will ignore 183 Progress
> SDP body and proceed with 200 (Ok) SDP body? (As per RFC 3261, UAC must
> ignore the SDP of 200 (Ok) if it has received SDP in provisional response).
> Secondly, If there will be no SDP body in INVITE message then how one can
> play announcent to Calling Party (UAC) if Calling party does not support
> reliable provisional response mechanism.
>
> Thanks in Advance
>
>
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