By drop connection do you mean the phone lose registration or lose network connectivity? On the phone's LCD right side there is an ethernet icon. If the border is lit then there is network connectivity and if border and inside is lit then it mean register and network connectivity is established. If the phone is behind NAT and losing registration periodically, we suggest to enable the following keep alive features on the web UI of the phone:
1. Account->Network settings->NAT traversal-> set to keep alive
2. Account->SIP settings->Basic settings->Enable OPTIONS keep alive-> set to Yes
Let us know if above settings help with your situation.