[Asterisk-Users] Help with strategy for echo cancellation.

[Shilliday, Jim]

I have just installed * (RH9, P4 3.0GHZ, 1G RAM) in a small office,
using three TDM400's with 4 FXO's each for incoming calls.  Outgoing
calls are (for the moment) routed via VoicePulse.  Phone sets are Cisco
7940G's using SIP.  I'm getting intermittent echo on outgoing calls, and
my understanding, based on reviewing the wiki and several posts here, is
this:

	>>>>  The source of the echo is the analog tail circuit at the
far end of the call.  This is consistent with the facts -- I don't have
echo on internal calls or on IAX2 calls to another Cisco 7940 on another
* box.
	>>>>	 There's nothing that I can do about the echo using *
echo cancellation because (according to Cisco's Echo Analysis paper) my
echo cancellation only deals with echo originating at my end.  (Am I
wrong?  Hope so).
	>>>>	 I may be able to minimize the problem by tweaking the
Rx/Tx gain in zapata.conf.  

So, if my understanding is right, can someone please suggest a strategy
for adjusting the gain controls?  There are two controls, and each can
be adjusted up or down.  I'd like to adopt a method other than random
fiddling.  Where's a good place to start?  

Thanks!

Jim Shilliday
IT Director
Equal Justice Center
1315 Walnut St. Suite 400
Philadelphia PA 19107
215-238-6970