[SIPForum-discussion] SDP Body in 183 Progress Message

[M. Ranganathan]

On Tue, Mar 16, 2010 at 4:25 PM, Nitin Kapoor <nitinkapoorr at gmail.com>wrote:

> 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.
>


This is not quite right. Consider a forking scenario where a client
transaction is forked downstream to multiple locations. Each one can return
a provisional response with a different SDP.

What is true is the client transaction will pick one of these and cancel the
other branches.



>
> 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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-- 
M. Ranganathan
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