Asterisk performs echo cancellation for all incoming and outgoing calls through the T1/PRI card.  However, there are some things that can still cause echo's.  We had a similar situation a with a setup much like yours.  We switched to the MG2 echo canceller which helped quite a bit.  But finally, after testing everything else we possibly could, swapping out PRI cards, changing every concevable setting related to echo, and having the phone company out about a dozen times to check the PRI, we ended up switching companies from Telepacific to Sprint and the echo problem, according to the users, completely went away.
 
However, a couple things you may want to look at is the audio gain settings in your zapata.conf and make sure they're not set too high, maybe even try dropping them down a bit.  And try the MG2 echo canceller if you haven't already, it seems to provide the best results on PRI's, at least as far as our testing has gone.
 
Erick

 
On 1/3/06, Aaron Daniel <[EMAIL PROTECTED]> wrote:
We currently have about 60 cisco 7940's, which were converted from cisco
call manager to be used for asterisk.  We're running 1.2.1 stable on 4
systems (primary server, backup server, gateway, and voicemail).  The
phone lines come into the gateway on a digium te405p.  The problem we're
having is that the 7940's are echoing on outgoing calls, and I'm not
sure what else to try (I did just recompile zaptel with a different echo
canceler to see if it would help), but I seem to remember asterisk
doesn't do echo cancellation on outgoing calls.  I researched a bit on
qos and latency, but there's maybe a 10ms latency between the phone and
the outgoing line, so I ruled that out pretty quick.  Any help is
greatly appreciated.

Aaron

On Tue, 2006-01-03 at 21:26 -0800, Erick Baum wrote:
> Can you provide some details about the system, what version of
> Asterisk, what kind of phones, what kind of phone lines, etc.
>
> Erick
>
>
> On 1/3/06, Aaron Daniel < [EMAIL PROTECTED]> wrote:
>         I've got a slight problem with echo.  Basically, most of the
>         outgoing
>         phone calls on our system echo, but as far as I can tell, the
>         incoming
>         echo has been relatively fixed, with just a bit of work left
>         to do on
>         it.  I read somewhere that asterisk doesn't echo cancel on
>         outgoing
>         calls, am I wrong in that assumption, and if I am, what else
>         can be done
>         when the echo training and echo cancel tapping isn't working?
>
>         Aaron
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