[Asterisk-Dev] Fax detection, handling and bridged calls?

john harragin jharragi at mw.k12.ny.us
Mon Jan 26 14:29:03 MST 2004

I've been getting echo on bridged calls with echocancelwhenbridged=no. It 
appears that many of my toshiba pbx (connected with an em_w T1) calls are 
being detected as fax calls. 'Fax Detected, but no fax extension'. In 
'zap show channel' 'echo cancellation' is indeed off - but 'Fax Handled' 
is yes. This is introducing some pecular echo. 
I have not yet determined why this is happening - I have some centrex 
trunks on the pbx. Perhaps it is sending * some centrex stuff that is 
being interpreted as fax tones. I'm still looking... but this behavior 
still leads to some questions. 
I suspect 'fax handling' should probably bi-pass on bridged calls with 
echocancelwhenbridged=no - but as a non-user of this feature, I'm not 
sure what all of the benefits are. Whatever, it seems that nothing good 
can come from adding delay to a psudo-tdm fax call. In this case the call 
should merely be routed to a fax extension if desired. Am I overlooking 
Anyway, in this particular case, it would be fine to disable fax 
detection & handling completely. Can this already be done? 

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