Hi Benny, I am trying to add Fax Tone detection support in PJSIP, I want to trigger my upper application about the Fax Detection, for that I need Event Call back from Media i.e. Fax tone has been detected. After going in some details of PJ-Media code I came across that this it is quite similar like detecting RFC2833 (Digit) Event i.e. Register Event as soon as the call is connected in pjsua_call.c in pjmedia_session_set_dtmf_callback function. I came out to this solution only. I need the better way of doing it, if it is available. Looking forward for quick response. Thanks & Regards, Ravi Inder Singh