I&#39;m trying to reliably detect whether there is a fax machine on an incoming channel.<div><br></div><div>Right now, it works nicely with the following dial plan:</div><div><br></div><div>       answer</div><div>       spandsp_start_fax_detect</div>
<div>       sleep 5000</div><div><span style="background-color: transparent; ">       spandsp_stop_fax_detect</span></div><div><span style="background-color: transparent; ">       [... no fax there, so now do stuff that has nothing to do with fax ...]</span></div>
<div><span style="background-color: transparent; "><br></span></div><div><span style="background-color: transparent; ">If the remote end is a PSTN fax, spandsp will fire an event upon detecting the CNG tone, and I will react accordingly.</span></div>
<div><span style="background-color: transparent; "><br></span></div><div><span style="background-color: transparent; ">However, if the remove end is a T.38 fax, which will immediately re-invite after answer, then the following problem occurs:</span></div>
<div><span style="background-color: transparent; "><br></span></div><div><span style="background-color: transparent; ">FreeSWITCH does not answer the re-invite (just says 100 Trying and nothing follows). Even though the remove end fax transmits the CNG tone afterwards, it is not detected by spandsp. I have recorded the call to make sure the CGN tone is there, and it is there. I have even played this tone into another phone call, where it is successfully detected by spandsp. All I can guess is that the non-answered re-invite might block spandsp from detecting the tone?</span></div>
<div><span style="background-color: transparent; "><br></span></div><div>Greetings,</div><div>Roland</div><div><br></div>