In the server SQLNET.ora
do the following


Parameter: SQLNET.EXPIRE_TIME

Format: SQLNET.EXPIRE_TIME = minutes

Purpose: Sets an expiration time for Net8 sessions. The expiration time represents an interval that is specified in terms of minutes. The clock begins ticking when a connection is made. At the specified interval, Net8 verifies that the connection still exists. If the probe fails, the Net8 session is terminated.

SQLNET.EXPIRE_TIME=10