[asterisk-users] Disabling Echo Cancellation on a per Call basis

[Kevin P. Fleming]

Tobias Wolf wrote:

> If it is not possible, why is that so ? Is there really no need to do this and i 
> am totally mistaken?

This is generally true. Any standards-compliant FAX machine or modem
will generate a CED tone during the beginning of the call process, and
any standards compliant echo canceler (including the ones in
Zaptel/DAHDI) will respond to this tone by disabling the echo canceler.
With Zaptel/DAHDI and a software echo canceler, you can see the evidence
of this by watching the kernel message log for messages of the form
'Disabled echo canceler because of tone (..) on channel...". If a
hardware echo canceler is in use, there won't be any messages generated,
but it is still happening.

> Generally receiving faxes works fine, but sometimes they break and i assume i 
> might have something to do with echo can.

Unfortunately that is not likely to be the cause of your problems.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kpfleming at digium.com
Check us out at www.digium.com & www.asterisk.org