Alert log Show error for Database connectivity error.

Database loss connectivity with Client adn server itself.
2013-01-28 04:20:44.541000 +05:30

Fatal NI connect error 12170.

  VERSION INFORMATION:
TNS for Solaris: Version 11.1.0.7.0 - Production
Oracle Bequeath NT Protocol Adapter for Solaris: Version 11.1.0.7.0 - Production
TCP/IP NT Protocol Adapter for Solaris: Version 11.1.0.7.0 - Production
  Time: 28-JAN-2013 04:20:44
  Tracing not turned on.
  Tns error struct:
    ns main err code: 12535

2013-01-28 04:20:50.789000 +05:30
TNS-12535: TNS:operation timed out
    ns secondary err code: 12606
    nt main err code: 0
    nt secondary err code: 0
    nt OS err code: 0
  Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=111.11.11.111)(PORT=36221))
WARNING: inbound connection timed out (ORA-3136)


After frequenly getting this error. I have increase sqlnet.ora parameters.