[Asterisk-Users] Strange echo phenomenon (double tandem)

[Martin Joseph]

I have a strange problem with echo.

My setup includes a Grandstream HT-488 which is both an FXO and a FXS.

I noticed last evening that if I called the FXS through my asterisk box 
from my cell, the resulting connection was fine for me at the cell end, 
  but produced dramatic and conversation ruining echo at the FXS of the 
HT-488.

Today I realized that if I call out from the same FXS to my cell, the 
conversation sounds great at both ends?

At first I wasn't disturbed by this, as I thought perhaps there was a 
different codec being used or something? But cranking up the verbosity 
and checking this theory shows they are both using g729.

I tried a different cell with a different wireless service provider and 
the result was identical.

Any thoughts on why this might be, and ideas on how it might be fixed?

Thanks,
Marty

PS Current asterisk as of 1/30/2006