[Serusers] Problem with CANCEL messages and Cisco 7905

Hey! This is my first time posting to the list, although I'm a long time reader :) I have searched the archives as well as the internet and found no solution or answer to this so far. Perhaps my Google Kung Fu isn't what it should be. Anyhow, I have a cisco 7905 phone working together with a SER machine. When dialing to the 7905 phone from another phone and hanging up on the caller phone before answering the 7905, ie CANCEL before the call has actually been setup, I get a "SIP/2.0 481 Call Leg/Transaction Does Not Exist." back from the Cisco phone. It's a pretty basic configuration (basically the one used in the examples for call forwarding). What I want to know is how the phone identifies a Call Leg/Transaction. I have used ngrep quite extensively and found nothing. Most values in both the INVITE and CANCEL message are equal. I've also got a Thomson ATA box which does not show the same behaviour despite being connected to the same SER. What values are used to identify a transaction, how can I see if two messages are of the same transaction? Perhaps this is actually a user agent problem, but I don't really know where to turn for help with this 7905 (Cisco only provides support if you use their Call Manager solution). regards, Kristian. -- Kristian Larsson KLL-RIPE Network Engineer Net At Once [AS35706] email: kristian(a)netatonce.se irc: kll@ircnet phone: +46 470 592717 cell: +46 704 910401