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

[Steve Davies]

On 7/17/06, Chan Kwang Mien <kwangmien at asgent-tech.com> wrote:
> Hi Paul,
>
> Thanks for your reply.
>
> The purpose of my tests is to verify that Echo Cancellation is up and
> running in the zaptel-1.2.6 that I have installed.
>
> In my test-bed,
>
> IP Phone A <------> Asterisk IP PBX <---> Analog Phone B
>
> IP Phone A is a speaker phone which I think doesn't have its own
> acoustic echo canceller.
>
> IP Phone A is one hop away from the Asterisk IP PBX and the Analog Phone
> B is directly connected to the FXS port of a TE400P Digium Card in the
> IP PBX.
>
> 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 ?
>

Zaptel is responsible for trying to cancel echo received on a Zaptel
interface, and is not particularly involved in the communication with
"IP Phone A", so your test is invalid in that you are testing Zaptel
against something it has no responsibility for.

You should generate the echo at the analogue phone, and listen at the
IP phone if you want to test Zaptel. This also represents the "real
world" case more accurately.

Cheers,
Steve