UA1                 Kamailio                 UA2             Media Server
Invite ---------------->                                                    - Received a normal Invite
                       Invite---------------->                              - Forward The Invite
                       <------------------200                               - Receive the 200 OK
<------------------200                                                      - Forward the 200 OK
<-------------re-Invite re-Invite ------------>                             - Kamailio will update the media part to the Media Server
                                              <----RTP Announce 1----->     - RTP are established
<----------------------RTP Announce 2 --------------------------------->    - RTP are established
<-------------re-Invite re-Invite ------------>                             - Kamailio after the announcement are finished update the Media part to UA1 ip media and UA2 ip media
<-----------------RTP------------------------->                             - RTP between UA1 and UA2