Module or Location of file for fax_detect


#1

Centos 7
Asterisk 13

Question:
Amateur programmer here but I want to try to attempt to look through the ‘C’ codes. Could someone direct in the right direction. Where is the module for file of ‘fax_detect’ which the bool is usually located in pjsip.conf.

Goal:
I want to see the frequency that asterisk is listening on. From my understanding fax incoming generates a freq tone on 1100 hz but when trying to detect fax on outgoing, it generate a tone of 2100 hz correct me if im wrong so I was wondering if I can edit the AMD function and add additional parameters to the function to listen on outgoing/incoming fax tone within dialplan.

Reference: Tone http://what-when-how.com/voip/fax-and-modem-tones-basics-voip/


#2

These frequencies are defined by ITU standards, and it would probably be better to refer to those directly than to reverse engineer Asterisk.

A secondary source would seem to be http://what-when-how.com/voip/fax-and-modem-tones-basics-voip/

Incidentally 2100Hz is used by many modems, not just those used for fax, and it is really there to signal to, particularly analogue, networks that a full duplex path, with no echo suppression, is needed.