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.
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.