[asterisk-users] Very Loud (+Echo/Reverb) issue with TDM400P+fax detection (UK)

[Gordon Henderson]

Interesting problem - small server with a TDM400P card, one FXO and one
FXS module.

The dialplan (amongst other things) routes an incoming call from the PSTN
no the FXO port to to the FXS port, and a number of SIP phones.

There is a fairly standard DECT phone with handsets round the office
connected to the FXS port, and all was going well until I added fax
detection. Do get it to work, I needed to up the rxgain on the incoming
line to 7, but this seems to have caused a weird effect on the internal
DECT phone - it's now very loud and it's the volume that (I suspect) is
causing a local echo (it's more like reverb)  issue. The far-end doesn't
seem to hear it, and it happens for both incoming and outgoing calls (made
from the internal analog/DECT phone)

Whats really odd is that if the incoming call is picked up on a SIP phone
then you don't seem to get this loudness/echo/reverb issue.

Am I missing some magic config in the zaptel.conf file, or any other clues
to make it work? I can "fix" it by tunning off fax detection and
commenting out the rxgain line, but fax detection is a desired feature in
this case... (and it's working very well too - fax to email, woo hoo!)

I've tried this on 2 different systems with different makes of dect phone
(and 'real' analogue phones) and it's the same, so I'm sure it's not a
hardware fault thats the problem...

Asterisk 1.2.10, zaptel-1.2.7, Linux 2.6.17.x, Debian Sarge base and based
in the UK if that's any additional help...

zapata.conf below:

[channels]
usecallerid=yes
cidsignalling=v23 ; Added for UK CLI detection
cidstart=polarity ; Added for UK CLI detection
hidecallerid=no
callwaiting=no
threewaycalling=yes
transfer=yes
echocancel=yes
echotraining=yes
immediate=no
;faxdetect=incoming

context=internal
signalling=fxo_ks
sendcalleridafter=2 ; the hidden option given by Slav from Digium
mailbox=100
callerid=100
channel => 4

context=incoming
signalling=fxs_ks
;rxgain=7.0     ; Need this for incoming FAXes
immediate=no ; will take the line on the first ring
callerid=asreceived ; propagate the CID received from BT
channel => 1


Thanks,

Gordon