Keep Getting Connection Lost Oracle Error ORA-03135

I moved this question over from the SQL Server Disucssion....

Hi All,

Sorry guys, I was not able to find an Oracle database community to start the discussion, so i am posting here.

I  have an issue with oracle database servers running on ESXi 5.1. The  connection to the databse servers are getting disconnected after 1 hour  of inactivity. I am connecting with sqlplus. The error i am geting is

05-MAR-2013 10:20:33

SQL> select to_char(sysdate, 'DD-MON-YYYY HH24:MI:SS') from dual;

select to_char(sysdate, 'DD-MON-YYYY HH24:MI:SS') from dual

*

ERROR at line 1:

ORA-03135: connection lost contact

Please advise

Regards,

Aneesh