[asterisk-users] Question about echo cancelation

[Eric "ManxPower" Wieling]

All calls with a 2-wire analog piece have echo.  You cannot perceive the 
echo because it happens so fast on non-VoIP connections.  On VoIP calls 
you have significant extra latency while causes you you to perceive the 
echo.  Echo must be removed before the call is converted to VoIP -- in 
your case the Media Gateway is the device that must remove echo.

Olivier wrote:
> 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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