This would be awesome because (as you say) you can't count on the receiving machine sending the 2100Hz tone... On Thu, Apr 14, 2011 at 1:58 PM, Steve Underwood <steveu@coppice.org> wrote:
On 04/15/2011 01:32 AM, Christopher Rienzo wrote:
2100 Hz is the ANS tone from the receiving side of the fax call. That's what I detect on my outbound calls. An answering machine sends 2100Hz, but its very unreliable to rely on hearing it. In spandsp there is a module which does a much more thorough job of detecting a FAX machine. It will accept the V.21 preamble, which normally follows the 2100Hz tone, as a substitute for the 2100Hz itself. That way a call which starts passing audio a bit late (which they often do) still results in proper FAX detection. We need to expose that functionality in FreeSwitch, but have not done so yet.
Steve
-- Kristian Kielhofner