[Asterisk-Users] Tiny Echo on PSTN via Zaptel

[Shaw Terwilliger]

I'm using Asterisk 1.0.9, a Digium TE210P dual T1 card, and two Rhino
channel banks (one 12FXO/12FXS, the other 24 FXS).  So it's an analog
phone on the inside connected to one of the FXS ports, and PSTN line
connected to one of the FXO ports.

My problem is that as soon as I hear the _first_ ring when I dial out 
through the PSTN line, I hear a tiny echo on the phone (I estimate
between 20ms and 40ms), which never goes away for this call.  It's just 
loud enough to bug the heck out of me when I'm talking (I could estimate
the gain relationship with ztmonitor if it would help).  The sound
on the recipient end of the connection is perfect.

If I make a call from the phone to the another internal extension (another
phone on an FXS port), there is no echo.  If I call into Comedian mail,
there is no echo.

I've checked all my gains.  The "internal" gains were a bit loud to start
with because of the powered phones, but now they all fall comfortably within
ztmonitor's dynamic range display.  The PSTN line is pretty good at tx 0 and
rx 0, so I left it.  I've tried turning them down, but that didn't kill
the echo.

My zapata.conf includes these lines at the bottom:

echocancel=yes
echocancelwhenbridged=no
echotraining=yes

context=companyA-pstn
txgain=0.0
rxgain=0.0
signalling=fxs_ks
group=1
channel=1-7

context=companyB-pstn
txgain=0.0
rxgain=0.0
signalling=fxs_ks
group=2
channel=11-12

context=internal
txgain=-12.0
rxgain=-8.0
signalling=fxo_ls
callerid=asreceived
group=3
channel=13-48

When the calls are connected, I can use "zap show channel 11" and verify
that the echo cancellation is ON.  But I can still hear one.
I've also tried echocancelwhenbridged=yes, but it didn't make any difference.

-- 
Shaw Terwilliger <sterwill at sourcegear.com>
SourceGear LLC
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