Operation not compleated lost connection to server

Hi
I have run query using sql developer. It takes hours and finally getting stuck the connection. In trace files I have found this messages. Whats going on with this


Fatal NI connect error 12170.

  VERSION INFORMATION:
        TNS for IBM/AIX RISC System/6000: Version 11.2.0.3.0 - Production
        TCP/IP NT Protocol Adapter for IBM/AIX RISC System/6000: Version 11.2.0.3.0 - Production
        Oracle Bequeath NT Protocol Adapter for IBM/AIX RISC System/6000: Version 11.2.0.3.0 - Produ
ction
  Time: 02-JAN-2014 10:48:10
  Tracing not turned on.
  Tns error struct:
    ns main err code: 12535

TNS-12535: TNS:operation timed out
    ns secondary err code: 12560
    nt main err code: 505

TNS-00505: Operation timed out