[asterisk-users] Help! Echo problem even at T1 PRI?

[Matthew Fredrickson]

On Mar 15, 2007, at 10:34 PM, Vincent Tam wrote:

> Hello,
>  
> We have an asterisk setup at our client's site using a TE205P. The 
> line to telco is a 23 channels T1 PRI, however the line has random 
> echo problems (about 5-10% of the calls)!
> Can anybody tell me if echo cancellation is really needed even at a T1 
> PRI to the telco? Because people keep saying when they deploy voip 
> solution in Hong Kong using T1 PRI, there is no need of echo 
> cancellation. (even the local Digium distributor)
>  
> Asterisk is 1.2.13, zaptel is 1.2.10. I choosed the MARK2 canceller in 
> the zaptel.
>  
> The setting in zaptel is default:
> echocancel=yes
> echocancelwhenbridged=yes
> echotraining=yes
> rxgain=0
> txgain=0
>  
> When I tried to adjust the echocancel value to a higher taps (e.g. 
> 256) or adjust the rxgain/txgain value, I can even hear echo much 
> easier.
>  
> Anyone can confirm with me we should rather turn 
> echocancelwhenbridged=no, or even echocancel=no when we only use a T1 
> PRI at the zaptel? Or can have other suggestions to try solving this 
> problem? Because of some people's information that T1 PRI does not 
> need any echo cancellation, add a hardware echo cancellation module is 
> not an option here.

Use the HPEC.  It'll solve any echo problems you might have.  You can 
set your tap length on it so that it might be possible to get a span or 
two's worth of echo cancellation on a decent machine.

If the HPEC is too much, KB1 is the best in 1.2, but MG2 from 1.4 is 
probably the best of the low CPU usage echo cancellers.

Matthew Fredrickson