[asterisk-users] Question about echo cancelation

[Olivier]

Hi,

I'm using the following setup :
Alice ---- IPPhone ------<LAN>----- Media gateway ----<PSTN> ------- Phone
---- Bob

For certain calls, users complains about echo : they can ear their own voice
in their handset, though media gateway echo cancel is turned on.

I'm wondering how this echo cancelation engine is supposed to work.
My understanding of echo is that most probably, when users complains about
earing their own voice, that means that distant phone or nearby equipment is
"leaking" : Bob's phone is sending Alice's voice signal back to Alice.

So, to properly cancel, I would say Media gateway should substract from
incoming signal the signal that left the media gateway few ms before.

Discussing here and there, some say that Media Gateway never work this way :
it would only filters out locally generated echo.
Do you agree with that ?
If positive, then what can you do, if Bob's phone generate much echo ?

Regards
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