I have seen a potential problem in the bis05 state machine. This problem is specifically in the INVITE client transaction state machine. It is stated that if a 2xx is received in the 'calling' or 'proceeding' states that the UAC core will automatically generate an ACK in response. This causes a problem when the session offer has been sent in the 2xx (as opposed to in the INVITE) in such a case the TU needs to answer this offer, and therefore it must generate the ACK. A corresponding potential problem is found in the INVITE server transaction state machine, where if a 2xx is sent from the TU the state machine transitions directly to the terminated state. This suggests that the TU never sees the ACK, and consequently would never see the answer part of any session description contained in the 2xx-ACK pair.
Chris Mills
