Please read this RFC 
 
tools.ietf.org/html/rfc4916

________________________________

From: [email protected] on behalf of Volkan Hatem
Sent: Fri 5/28/2010 2:02 AM
To: [email protected]
Subject: [Sip-implementors] Need clarification on RFC4916



Hi,

Unfortunately the RFC is not clear how 200OK & ACK are affected after
an early-dialog UPDATE. Please see the following call flow where in
the original INVITE From is Alice and To is Bob. After receiving 18x,
from-change UPDATE is sent with From set to Carol.

I'm confident that ACK must convey the same From/To headers as the
original INVITE. However I'm not sure about 200 OK to the INVITE
request after receiving UPDATE.

What do you think?

   Alice                               Bob
     |                                  |
     |                                  |
     |(1) INVITE                        |
     |(From:Alice, To:Bob)              |
     |--------------------------------->|
     |                                  |
     |(2) 18X                           |
     |(From:Alice, To:Bob)              |
     |<---------------------------------|
     |                                  |
     |(3) UPDATE                        |
     |(From:Carol, To:Bob)              |
     |--------------------------------->|
     |                                  |
     |(4) 200 OK (UPDATE)               |
     |(From:Carol, To:Bob)              |
     |<---------------------------------|
     |                                  |
     |(5) 200 OK (INVITE)               |
     |(, From:?, To:Bob)                |
     |<---------------------------------|
     |                                  |
     |(6) ACK                           |
     |(From:Alice, To:Bob)              |
     |--------------------------------->|
     |                                  |
     |                                  |
     |                                  |
     |                                  |
   Alice                               Bob
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