[Serusers] Forking Proxy

Hi All I have a question about the CORRECT operation of UA when making a call via a forking proxy: Lets say UA1 calls 7000(a)sip.com and user 7000(a)sip.com is available at UA2 and UA3 i.e. the Proxy forks the request. UA1 Forking UA2 UA3 Proxxy 1 |------INVITE---------->| | | 2 | |--------INVITE-------------->| | 3 | |---------------------------INVITE------------->| 4 | |<---RINGING(totag=1234)------| | 5 |<---RINGING(totag=1234)| | | 6 | |<------------------RINGING(totag=5768)---------| 7 |<---RINGING(totag=5678)| | | | | | | | | | | NOW UA3 WILL ANSWER | |<----------------200 OK (totag=5678)-----------| 8 |<-200 OK (totag=5678)--| | | 9 |---ACK (totag=1234)--->| | | 10 | |------------------ACK (totag=1234)------------>| AT THIS STAGE UA 3 IGNORES THE ACK AS IT DOES NOT CORRESPOND TO ORIGINATING 200 OK AND THE CALL IS NOT SETUP * UA1 is using the to-tag of the first 180 RINGING it received (frame 5) no matter what the to-tag in the 200 OK is * My question here is: who is in the wrong???? The proxy or UA1? * Should the proxy change the to-tag of the ACK before forewarding it to UA3??? Any help/guidance would be much appreciated Jason Penton Rhodes University Grahamstown South Africa