[cisco-voip] Listener Echo

Jason Aarons (US) jason.aarons at us.didata.com
Fri Feb 20 19:53:12 EST 2009

Despite whatever you read on CCO about 2-wire to 4-wire, try first
changing the phone load. You may want to try several loads before
chasing down a echo canceller, etc.

Older loads (2002-2003) had issues with the mic picking up the speaker
on 79x0s.

Also use a older 7940/60 measure the ERL and adjust input gain and
output attenuation as in the bottom of this article (this won't work
with 7941 or newer phones


-----Original Message-----
From: cisco-voip-bounces at puck.nether.net
[mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Ed Leatherman
Sent: Friday, February 20, 2009 4:51 PM
To: cisco voip
Subject: [cisco-voip] Listener Echo

Anyone had to troubleshoot listener echo?

I've been reading up a good bit on echo from some docs on CCO, but
it's all related to talker echo. So far what i've googled up gives a
good definition of listener echo, but nothing really on how to address

The symptoms some of my call center agents have reported are where
they are hearing an echo of the caller rather than themselves. The
echo is very close to the "real" audio from the caller, so i think if
there was just a little bit less latency out where its getting
generated, it wouldn't even be perceptible. My call center itself is
on our campus LAN, network latency between them and the PSTN gateway
is by and large under ~4ms based on my IPSLA stats.. but I don't think
this leg of the call has anything to do with the problem.

This doesn't seem like it can be fixed with the echo cancelers on my
gateways, at least in my limited understanding of how they operate (no
transmit signal to compare to). This call center deals primarily with
pharmacies (walgreens, walmart, supermarkets, etc). If I can find some
sort of pattern here and establish that it's callers from a specific
phone number or company, is there something on my side I can even do
to fix this?

I told them to make sure the caller wasn't on a speaker phone and try
to establish some sort of pattern of problem calls.

Ed Leatherman
Assistant Director, Voice Services
West Virginia University
Telecommunications and Network Operations
cisco-voip mailing list
cisco-voip at puck.nether.net


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