What the reason of error "ORA-03135: Connection lost contact" when migration Microsoft OracleClient to ODP.NET
Networking problems can be some of the trickiest to diagnose without help. First of all, you should contact the DBA for the database in question and ask them to help you.
Have your DBA look into the logs to see if he can find anything. A firewall could be killing the connection. Or SQL Net could be configured to time out connections.
Does your company have a support contract? If so, I would open a SR and they can help you trace things to narrow down the problem. You will need the cooperation of your DBA to look at the server side.