[asterisk-dev] Queries regarding Echo Cancellation in Zaptel-1.2.6

[Nicolas Bougues]

Le lundi 17 juillet 2006 11:04, Chan Kwang Mien a écrit :
> Hi Paul,
>
> To simulate echo, the call at IP Phone A is being answered by its
> speaker. I was expecting that the echo sent back by IP Phone A to Analog
> Phone B would be cancelled by the echo canceller at the IP PBX. But it
> seems that I could still hear echo although I have enabled echo
> cancellation in zaptel.
>
> Do you know why I could still hear echo at Phone B ?
>

As Paul told you, there are usually two sources of echo : 
- either for the PSTN hybrid connecting the FXS
- or from some poorly designed phone (usually in handsfree mode)

EC in Asterisk is meant to cancel line echo, the first kind.

So in your setup, it means that when you are on the A side, you won't get 
(line) echo from the B phoneline. You should try to disable EC, and hear echo 
in the A phone.

IP phones are supposed to be "4 wire equivalent". It means that there is no 
hybrid, and no natural "mixing" of inbound and outboind audio. So no matter 
where you're calling from, you shouldn't get echo from any phone calling a 
VOIP phone. So Asterisk doesn't implement an EC on that side of the call.

If you're getting some echo, it's simply that your phone does generate it by 
itself, maybe in handsfree mode, and the only fix is switch or fix your 
phone.

-- 
Nicolas Bougues