Subject: Re: [Sip-implementors] [Sip] PRACK query

From: Paul Kyzivat <[email-masked]>
Date: Sun, 01 Oct 2006 22:11:24 -0400

[email-masked] wrote:
> SDP in 1xx response and 200 OK can be different because of early media 
> announcements and actual calle connected.
> 
> If 200 OK SDP will be same, then how can early media will be 
> differentiated with regular session
> (basically early media is used for announcements and 200 OK will tell the 
> actual callee connected)

You cannot just change the SDP between the 18x and 200 because of early 
media. In a single dialog these are required to be the same. (Or, if the 
18x was reliable, then the SDP in the 200 can (should) be omitted.

Another possibility is that you get a 18x with SDP in one dialog, and a 
200 with a different SDP in a different dialog.

In general you can't differentiate between early media and regular 
session media when using the "gateway model". (See the early media RFCs 
for more detail.)

	Paul

> Regards,
> Udit
> 
> 
> 
> 
> "Christer Holmberg \(JO/LMF\)" <[email-masked]> 
> 09/28/2006 07:46 PM
> 
> To
> Udit Goyal/C/US/3Com@3Com, <[email-masked]>
> cc
> [email-masked]
> Subject
> RE: [Sip] PRACK query
> 
> 
> 
> 
> 
> 
> 
> Hi,
> 
>> Please let me know if my understanding is correct for regular session
> offer-answer when PRACK is used:
>> For INVITE containing SDP, and if offer answer done in the using
> reliable 183 response for early media, 200 OK response SDP will have an
> answer for the
>> regular session, so 200 OK SDP will be answer to the offer sent in
> initial SDP.
> 
> Yes.
> 
> Of course, since you have already received the answer reliably, you
> really don't need to care about the SDP in 200 OK, but according to the
> rules it should be the same as previously sent in 18x.
> 
> 
>> Similarly, if INVITE does not  have SDP, and if offer-answer done using
> PRACK, still 200 OK will contain the regular session offer and answer
> will be
>> present n the ACK message.
> 
> I would assume so, yes. But, again, you don't really need to care.
> 
>> Similarly, if UPDATE is used for offer-answer before call is connected,
> it will not affect the regular session offer-answer, it will be taken
> care by
>> initial INVITE , final 200 OK and ACK message.
> 
> I don't know what you mean by "not affect".
> 
> If you send an offer in INVITE, and receives an answer in a reliable
> 18x, the offer/answer exchange in UPDATE will then replace the one
> previously done.
> 
> But, yes, the SDP you get in the 200 OK should still be the same that
> you got in 18x, even if you have performed offer/answer exchanges after
> that.
> 
> At least this is how I understand it - but you can never be sure when it
> comes to offer/answer :)
> 
> Regards,
> 
> Christer
> 
> 
> 
> 
> _______________________________________________
> Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> This list is for NEW development of the core SIP Protocol
> Use [email-masked] for questions on current sip
> Use [email-masked] for new developments on the application of sip
> _______________________________________________
> Sip-implementors mailing list
> [email-masked]
> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
> 

_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip