[Asterisk-Users] Anyone using * in a live production environment?

[Stephen R. Besch]

Jorge Mendoza wrote:

> I'm in agree with all explanations regarding the echo and 2/4 wires 
> conversion. However I'm wondering if there are other parameters like 
> CPU and/or Asterisk configuration involved in the problem with more 
> weight than hybrid. Otherwise how do you explain the difference in the 
> following scenario:
>
> 1.- Crystal clear voice:
>
> [phone1]----[pabx]-----[fxo gateway]------SIP-------[fxs 
> gateway]------[phone2] 

>
> 2.- A lot of echo:
>
> [gnophone or xten]---[ * ]---------------SIP-------------[fxs 
> gateway]-----[phone2] 

First, I assume that the right hand side in both cases is the same.  
Then determine where the echo originates. I would guess that it is 
either coming from the fxs gateway and that there is no echo 
cancellation running on the fxs, while there is on the fxo, or you are 
using an open mic and speaker on the softphone.  In the first case, when 
the fxo is in the circuit, the echo canceller sees the echo - it doesn't 
care where it comes from, the signal will stii autocorrelate because it 
contains a copy of itself - and it gets removed.  In the other case, the 
echo does not get removed because the echo canceller is not running on 
that channel.  Examine the channel status (zap show channel x) and the 
canceller is active when a call is in progress.  In the second case, use 
a headset. Echo cancellers are notoriously poor at cancelling room echo 
very well without very compute intensive algorithms and long tail 
lengths (lots of taps).  It usually reguires a DSP. If it's neither of 
these, then I am stumped.

>
> The first scenario has four 2/4 W conversion.

Well, I only see two possible hybrids here, unless the PABX is running 
analog at the external ports and digital internally -nutty, but possible.

> The second one has only two (or one?). 

Probably one.

>
> The * was running in differents CPU, PIII 500 Mhz, PIII 750 Mhz, 128 
> Mb to 512 Mb ram with not difference on echo.
> We have installed a Mitel 3100 with IP phones at 40 kms within a 
> wireless network with not echo at all.
>