[Serusers] problem cancelling a call with CANCEL request

[Esteban Monturus]

	I am installing a SIP proxy in a Linux machine in the local network of my 
office. I have implemented a SIP proxy with SER 0.8.10. The function of the 
SIP proxy is to let users talk each other without knowing the IP where each 
one is reachable. My problem appears when the caller wants to cancel the 
call because the callee does not answer. Since I want the calle's phone to 
stop ringing, and I haven't received a final response, the caller's phone 
has to send a CANCEL request. When the proxy server receives the CANCEL, it 
replies with a 487 "Request cancelled". SER does this before forwarding the 
CANCEL to the callee's phone. These 487 response generated by SER makes the 
INVITE client transaction of the caller finish. When the INVITE server 
transaction finishes in the callee's phone, it sends another 487 response, 
which is forwarded by SER, but the caller's transaction is already 
finished, so it doesn't send the corresponding ACK.

	I would like to know how to solve this problem, since SER should wait for 
the callee's phone to send the 487 and then forward this response to the 
caller's phone.

	Best regards,

	Esteban.