When the call is made by Cisco Ip phone 7911 big echo is being heard during the conversation by the caller. The same call made by Cisco IP phone 7960 is excellent. Call statistics for the two calls are:
7911 Avg Jitter 1 Max Jitter 30
7960 Avg Jitter 1 Max Jitter 5
The firmware version for the 7911 is SCCP11.8-4-2S. I search for bug in the firmware but i can not find nothing. What can be the problem?