On Mon, 2009-04-20 at 16:56 -0400, Simon P. Ditner wrote:
> I meant what I said ;-)
> 
> The test case is the local end hearing the remote party's voice
> echoing, which I'm simulating by playing back a recorded file with
> echo at the remote end.

Ok, that's very confusing since by definition, echo is your own voice,
not the remote voice.... But I'm just going to assume you know what
you're doing ;)

> Since you're saying there is no such thing as a SIP echocan and by
> extension, I presume that the echocan on an FXO gateway won't cancel
> echo generated at the remote end either

Yes it will, that is the whole point of echo cancel. Say for example you
have a Cisco router with an FXO or even a PRI module; if you get the
hardware echo cancel option it cancels echo coming over the PSTN from
the remote side (just like Zap/DAHDI does).

> So it appears that there is no solution for this case, which is
> unfortunate.

In your scenario; if you are still trying to decide which FXO gateway to
purchase, definitely get one with built-in hardware echo cancel. They
are of course much more expensive but that is the correct solution.

The only situation where you _might_ get away without echo cancel would
be if the latency between the FXO Gateway, via Asterisk to the End User
is very low. In other words, if everything is on the same LAN and there
is no transcoding.

-- 
John Lange
http://www.johnlange.ca


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