Summary:ASTERISK-01369: Bad echo of DIS when sending fax
Reporter:zalex (zalex)Labels:
Date Opened:2004-04-07 14:42:37Date Closed:2011-06-07 14:05:13
Versions:Frequency of
Environment:Attachments:( 0) payload-04012004-1-backward.pcm.gz
( 1) payload-04012004-1-forward.pcm.gz
Description:Sending incoming (PSTN) fax to a local receiver (SIP).
Payload on the receiver side contains echo (attached) of DIS
tones. Tried MARK2 (with and without aggressive) set to
yes, 32, 64, 128, 256 (this one didn't work at all) and
MARK3, neither was good enough for receiver to take it as
incoming CNG. What can be done about it?


This is from the fax receiver developer:
"There is a stutter pattern having 20ms on / 20ms off.
The echo of one of the DIS frames is about 4 seconds long, but the original DIS is only 2 seconds long.  This seems to indicate that * is padding each of 20ms packets with an additional 20ms of silence when sending it out on the PSTN.
The stuttering nature of the signal may be what's preventing echo canceller from training quickly."
Comments:By: zalex (zalex) 2004-04-08 15:15:09

Here is the audio EC was supposed to train on.

By: Brian West (bkw918) 2004-04-08 17:49:42

well echo can should be totally off when sending a fax

have you tried it without ANY echocan?

By: zalex (zalex) 2004-04-09 12:44:15

With echocancel=no, echotraining=no, echocancelwhenbridged=no
echo is bad enough to prevent fax receiver from starting.

By: Brian West (bkw918) 2004-04-10 06:58:37

are you trying to fax over voip?

By: zalex (zalex) 2004-04-14 13:30:23

Please, disregard. The stuttering is due to the fax receiver
sending rtp packets with payload size and ts = 160 but doing it
every 40ms (not 20ms).

This is not * issue.