[asterisk-users] Bad Line Noise over T1

[Gleim, Jason]

I've got a system where I'm integrating a Nortel Option 11c with a
Trixbox 2.0.0 system using a Sangoma A101 T1 card. (Running on a Dell
PowerEdge 350)

We've got things mostly up and running and all seems well... except...
If I call from a SIP extension (X-lite soft phone) dialing 9xxxx where
xxxx is an extension on the Opt 11, the call goes through to the Opt 11
but I have terrible line noise in the earpiece of the softphone and
low/distored audio back out of it to the hard phone on the Opt 11. The
noise starts the moment the softphone goes 'off-hook' and the hard
extension starts ringing and only gets worse once the call is picked up.
(essentially white noise by then) Initially, during ringing, the noise
is pulsed... like when a cell phone is next to speakers and there is no
conversation on the line. Once the call is connected, the noise
essentially fills the gaps in the audio... almost like comfort noise
gone psycho. The noise reminds me of a modem when the carrier has been
established between two endpoints... that static sound. Except that it
clearly stops when there is audio on the channel.

I've checked the error counters on the A101 card before and after a call
and they look fine so it doesn't seem to be jitter or slip or anything
like that on the T1. I also tried the calls with 'echocancel' &
'echocancelwhenbridged' set to both yes & no in Zapata.conf. I've also
turned echo cancellation on and off on the A101 card using wancfg. I've
tried txgain and rxgain values from 0.0 to -10.0 with no affect.

Now, to really mess with things, if I dial another SIP softphone
extension on the Asterisk box (or IVR or VM), the audio is pristine so I
can rule out softphone problems and issues with the audio hardware on
the PC. (Plus, I've tested this from several softphones and they all
exhibit the problem.) It is only when I'm routing a call over that T1
that I get the noise. And to add to the mystery, the hard extension on
the Opt 11 has no noise on the line. If I talk into the hard phone, I
can hear it on the softphone perfectly but the noise fills all the gaps
in the audio. If I talk into the softphone, I can hear it on the hard
phone but the audio is a bit soft and distorted.

I'm stumped on this. I've never ran into this type of audio problem
before.
Has anyone seen this before and found a solution?

Below is Zapata.conf and Zaptel.conf

Thanks!
Jason

;
; Zapata telephony interface
;
; Configuration file

[trunkgroups]

[channels]
language=en
group => 0
context=from-zaptel
signalling=pri_net
switchtype => 5ess
callerid => asreceived
channel => 1-23

rxwink=300		; Atlas seems to use long (250ms) winks
;
; Whether or not to do distinctive ring detection on FXO lines
;
;usedistinctiveringdetection=yes

usecallerid=yes
hidecallerid=no
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes
echocancel=no
echocancelwhenbridged=no
echotraining=800
rxgain=0.0
txgain=0.0
group=0
callgroup=1
pickupgroup=1
immediate=no

;faxdetect=both
;faxdetect=incoming
;faxdetect=outgoing
faxdetect=no

;Include genzaptelconf configs
#include zapata-auto.conf

;group=1

;Include AMP configs
#include zapata_additional.conf




# Autogenerated by /usr/local/sbin/genzaptelconf -- do not hand edit
# Zaptel Configuration File
#
# This file is parsed by the Zaptel Configurator, ztcfg
#

# It must be in the module loading order


# Span 1: ZTDUMMY/1 "ZTDUMMY/1 1" 

# Global data

loadzone	= us
defaultzone	= us

# PRI to Nortel
span=1,0,0,esf,b8zs
bchan=1-23
dchan=24