[asterisk-users] HPEC > VPM ?

Noah Miller
Wed, 29 Jul 2009 13:51:14 -0000

Hi -

I had a client recently move their asterisk system (asterisk 1.4.26,
dahdi 2.2.0.1, aex800 w/vpm module) to a "new" location, a building
that's nearly 150 years old.  I was not personally able to go there,
but the person who did the move said the building's demarc room was
"scary"-- water leaks, jumbled and frayed wiring, and all sorts of
other fun.

The echo on their POTS lines has proven to be quite problematic.  The
hybrids are balanced, txgain and rxgain are optimized individually for
all channels, and the vpm module on the card is doing its job.  For
many calls, this has been effective.  Still, echo remains on calls to
some destinations, particularly those on the closer exchanges.  On
calls to one particular number, if I turn the echo canceler off, the
echo sounds as loud and clear as if the destination was actually
echo().  With the echo canceler on, echo is still very pronounced.
The echo tail is clearly longer than 16 ms.

I even tried disabling the vpm module (vpmsupport=0 in base.c) and
using oslec instead with a setting of echocancel=512.  After a long
convergence period, oslec seemed to do a slightly better job than the
vpm module, but echo was still bad enough to make a conversation
nearly impossible.

My question for anyone with knowledge on this: would HPEC do a better
job than the VPM module (or oslec)?  Can HPEC cope with very long echo
tails?


Thanks,
Noah