[cisco-voip] Echo on IP Phones through PRI

[Matthew Melbourne]

We are getting sporadic issues from users on IP phones who are hearing
echo on external calls. From this document is would suggest that echo
on IP Phones is caused by hybrid echo and not any local acoustic echo.

http://www.cisco.com/warp/public/788/voice-qos/echo_ipphone_gateway.html

The MGCP-controlled voice gateways are all running 12.3(14)T7 with DSP
firmware 4.4.708. In CallManager (4.1(3)SR2), echo cancellation is on
for each port, with a "default" echo cancellation coverage of 64ms.
Input gain and output attenuation are set to 0dB.

I have seen suggestions to include the "echo-cancel erl worst-case 3"
command on the voice ports. Can this help in situations of occasional
echo?

Are there any other parameters changes which could help? Could it be a
code/DSP firmware issue? I haven't found a specific echo-related bug
relating to this particular IOS and its embedded DSP firmware.

On occasions, the start of the call is fine but echo comes and goes
during the call.

Is there a quick way of finding out which voice gateway a call is
terminated on (we have 8, and all could be used in a round-robin
fashion for outbound calls).

Cheers,

Matt

-- 
Matthew Melbourne