[Asterisk-Users] Re: X100P / Echo / ZTMONITOR CAN2,3, etc.

[Stephen R. Besch]

Andrew Kohlsmith wrote:
>>If you're getting echo of your own voice, but the remote is getting a
>>clear signal, then Asterisk echo cancellation is working properly.  It
>>is the remote provider not echo cancelling properly.
> 
> 
> I don't buy it.  If that were the case then why would I not _also_ get my 
> own voice echoed with a regular phone plugged in to the same POTS line?
> 
And you shouldn't!  Theory holds that exactly the opposite is true. With 
no echo cancellation at all and with an unbalanced hybrid, the local 
party hears the echo and the remote party does not. This is because the 
local hybrid listens to itself talking to the pots line and sends what 
it hears back to the local listener. If the hybrid is perfectly 
balanced, it will subtract out what it is saying to the pots line before 
it returns the signal to the local caller. The problem is that it rarely 
does a very good job of this. Neither do many commercial channel banks.

There are a few common hardware glitches that can make echo a lot worse, 
such as a shorted leg or corroded connection in the PSTN wiring, having 
a hard wired extension connected to the same line or simply having a 
lousy CO switch at the other end.  The first 2 the phone provider should 
diagnose and fix for you.

The strange thing here is that asterisk is not removing the echo.  I did 
notice that the 0.7.1 tar did not do the echo cancel very well and Mark 
suggested that I go back to the CVS, which did wonders. You might also 
verify that echo cancellation is actually turned on. Enter "zap show 
channel x" at the CLI, where x is one of your defined zap channels.  If 
it's enabled, somewhere in the output you should see "Echo Cancellation: 
xx taps, Currently On/Off". The On/Off will change from Off to On when a 
call is bridged.  If it is not enabled, check the definitions in zapata 
and in your make file.