[Asterisk-Users] Long and variable echo

[James Andrewartha]

Kristof Hardy wrote:
>> The problem has been consistent from 1.0 through CVS to 1.2, and 
>> across different machines and distributions. Does anyone have any 
>> suggestions on how I can deal with this? I have had echo cancellation 
>> happening, but half-duplex speech is not acceptable.
> 
> You're not using zaptel, what are you using to connect to the outside? 
> (and is it PSTN/ISDN ?)
> 
> Can you advice on what hardware you're running, that would help..

I'm running Voicetronix hardware, the OpenSwitch 12 as 8 FXO and 4 FXS, 
connecting to the PSTN. The vpb software echo canceller does actually work 
somewhat, but it takes a long time to train, and if you stop talking for 30 
seconds it untrains.

But really, I shouldn't be getting echo at all - my hybrids are tuned right 
for Australian phones, and using the voicetronix measerl (measure echo 
return loss) utility I see a max of -10db.

Call path                            |Echo heard on|Echo recorded?
=====================================+=============+==============
landline FXO->asterisk->FXO mobile   | both        | both
FXS->asterisk->FXO mobile            | FXS         | FXS
SIP->asterisk->FXO anything          | SIP         | SIP
landline FXO->asterisk->FXS          | both ends   | both
landline FXO->asterisk->SIP          | SIP         | no
mobile FXO->asterisk->SIP            | SIP         | SIP
FXS->asterisk->FXO landline          | both ends   | FXO
landline FXO->asterisk->FXO landline | both ends   |
SIP->asterisk->SIP                   | none        | none

FXO landline is our current key system PBX, FXS is a little Jackson dialpad 
and headset, FXO mobile is calling out on an FXO through the PSTN to a GSM 
mobile.

In all cases, it's just the local end that hears themselves echoing.

What I want to know is why I'm seeing such long echos, of 180ms or more - 
from what I understand, packetisation delays should only be tens of 
milliseconds. It's not PSTN delay either - I'm calling lines on the local 
exchange. I'm at a loss to explain where it's coming from.

-- 
James Andrewartha
Systems Administrator
Data Analysis Australia Pty Ltd