I've faced this issue too.

There are just two UA's in my scenario. A - calling and B - called

When B's phone rings, A is played a personalized Ring back tone (song/music
etc.). For this I connect to a media server and the media server SDP goes in
a reliable provisional response to A. 

I cannot give A the media server the SDP in the 200 OK and then renegotiate
A & B (as per 3PCC call flows) as that would involve some charging issues. I
need to charge A only after B answers the call. But B answers with a
different SDP. 

I could use early session but not all UA's support that. 

What should I do in this case? Any thoughts?



-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Nathan Ning
Sent: Tuesday, October 11, 2005 12:26 PM
To: [EMAIL PROTECTED]
Cc: [email protected]
Subject: Re: [Sip-implementors] 183 Early Media with SDP

While there is real case that the UAC receives different SDP in 1XX and 200
OK,
and should not ignore the SDP in 200 OK.  Following is the case I met.

A, B, C are sip UE.
B owns sequential ring service(to C).
A calls to B, B rings but not to answer B,
timer expires, and C rings, C off hook.
A talking to C.

In the above case, when Invite request reach to B,
B may response with 183(SDP) firstly to connect A to a 
media server to hear announcement. While the first call
attempt will be cancelled, and when C off hook, A will
got a 200 OK (SDP) related to C.

thanks,
Nathan

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