Asterisk 11 Fax Detection - SIP/Outbound


I’m trying to detect if a call is answered by a fax machine on the remote end, dialing out via Asterisk on a SIP trunk. I can see in the SIP debugs that a re-invite with T.38 is sent but I’m having some issues determining how to handle the event. I’ve set faxdetect=yes in my sip.conf file (it doesn’t hand off to the ‘fax’ extension) and I’ve also attempted to grab the info from the sip_header function but can’t seem to isolate the T.38 messaging. I don’t need to process a fax once detected, I just need to know if it is receiving fax tone or re-invited with T.38. This is my first journey into Asterisk faxing so if I’ve missed anything basic, my apologies. Can someone suggest a way to determine if a SIP outbound call is answered by a fax device?