Core Issue
When you look at the packet capture you see that packets arriving at the Cisco CallManager server are not properly marked for Quality of Service (QoS). The issue is caused when QoS is not set correctly and network utilization causes the traffic to be dropped or delayed.
Resolution
In order to resolve the issue, set QoS trust on the switch port where Cisco CallManager is connected. Setting QoS on the switch port on which Cisco CallManager is connected, alleviates the problem enough for the devices to stop resetting.
For more information, refer to the Phone Resets section of Troubleshooting Guide for Cisco CallManager.
