I agree with Indresh. This isn't a valid call flow. The offeranswer
draft deals with this.
Paul
Singh, Indresh (SNL US) wrote:
> Fundamentally I think one can have one offer-answer in a single
> transaction. Which does not seems to be in the below case. There are two
> offers in INVITE transaction ( One in 180 and another in 200 OK ). So to
> me it does not look like valid call-flow.
>
> For early dialog cases to renegotiate media/change the offer UPDATE
> method should be used by UAS/UACs
>
> I do not know if this is specified in any specific RFC ( Offer-Answer
> RFC ) or SIP RFC. You may want to go through few earlier discussion on
> this subject
>
> https://lists.cs.columbia.edu/pipermail/sip-implementors/2005-July/00974
> 1.html
>
> Regards,
>
> Indresh K Singh
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of ext Bu,
> Wenfei (Leo)
> Sent: Thursday, April 05, 2007 1:13 PM
> To: [email protected]
> Subject: [Sip-implementors] Could the UAS change the SDP offer in 200
> OK?
>
> All,
>
>
>
> Take a look at the following call flow:
>
> UAC UAS
>
> -------->F1 INVITE w/o SDP
>
> <--------F2 180 w/ SDP1, Required: 100rel
>
> -------->F3 PRACK w/ SDP2
>
> <--------F4 200 for PRACK
>
> <--------F5 200 for INVITE w/ SDP3
>
> -------->F6 ACK w/ SDP4
>
>
>
> Is this a valid call flow? Could the UAS change its SDP offer in 200 OK
> for INVITE?
>
> If there's any RFC that clarifies this scenario, please let me know.
>
>
>
> Thanks,
>
> Leo
>
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