[Serusers] Problem with CANCEL messages and Cisco 7905

[Kristian Larsson]

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 at netatonce.se                      irc: kll at ircnet
phone: +46 470 592717                        cell: +46 704 910401