[Freeswitch-users] SIP Auxiliary Data and Notification

Hi, I’d like to send some auxiliary data via SIP during call setup and have freeswitch provide notification to an external process when that call setup is occurring and provide the auxiliary data. What would be the best way to achieve this? In particular, what events should I subscribe to in order to track call setups occurring in freeswitch in such a way that I can grab the auxiliary SIP data? Thanks.