asterisk users - Mar 2010 - Observation about DAHDI, FAX and Echo cancellation

Hi,

I have read that DAHDI automagically turns of echo cansellation when it sees
that it is a FAX.

So I checked this out. I have a fax call into asterisk which is immediately
called out to an external fax machine via DAHDI again..

For example, the result is: DAHDI/1-1 = incoming call, DAHDI/2-1 outgoing
call.

Now, with the help of dahdi show channel, if I check channel 2: echo
cancellation is ON. Then i check channel 1: it is OFF.

Shouldn't both be turned off?

Regards,
H?kon Nessj?en
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----- "H?kon Nessj?en" <haakon at avelia.no> escreveu:
> Hi,
> 
> I have read that DAHDI automagically turns of echo cansellation when
> it sees that it is a FAX.
> 
> So I checked this out. I have a fax call into asterisk which is
> immediately called out to an external fax machine via DAHDI again..
> 
> For example, the result is: DAHDI/1-1 = incoming call, DAHDI/2-1
> outgoing call.
> 
> Now, with the help of dahdi show channel, if I check channel 2: echo
> cancellation is ON. Then i check channel 1: it is OFF.
> 
> Shouldn't both be turned off?
> 
> Regards,
> H?kon Nessj?en
If I recall it correctly, Asterisk needs to listen to the CED tone to determine
if that call is indeed a fax or data transmission. Try to put an Answer() on
your dialplan.