[Asterisk-Users] Echo SIP-T100P-PRI

[Peter Svensson]

On Thu, 19 Aug 2004, Mike Schwartz wrote:

> 
> I'm experience echo on outgoing calls:
>   Snom 200 ----> Asterisk ----> T100P ----> PRI ----> called party
> 
> I am getting echo on the Snom 200 phone. The called party does not
> hear the echo. 
> 
> Since the PRI is digital, I don't really understand where the 
> echo is coming from.

Rule of thumb (i.e. a good starting point): if you hear the echo it is
coming from somewhere else, your equipment mearly makes it noticable. In
this case the echo is probably caused by an analog conversion at the
remote party. This is quite common but for calls with a very short latency
in the call path this is experienced as a reverb and not an echo.

The voip leg probably introduces quite a few ms worth of latency and thus
making the echo of your voice audiable. Since your digital end does not
introduce any echo at all the remote party does not hear any echo even
though the latency is the same in that direction.

When a pstn circuit is so long that the delay is enought for the echo to 
be noticed an echo canceler is typically introduced from a pool 
automatically. Common points for these to be enabled are for international 
circuits etc.

> I turned on echotraining, echocancellation=yes (128), and echowhenbridged
> in zapata.conf, to no avail. 

There have been a few reports that too little cpu power makes the echo 
canceler misbehave. You may want to reduce the number of taps from 128 as 
there have been reports that this helps.

Peter