Why satellite-sync fails with connection timed out error on Red Hat Satellite?

Issue

• On Red Hat Satellite server, satellite-sync fails to complete with following errors.

  SYNC ERROR: unhandled exception occurred:
  (Check logs/email for potentially more detail)
  ProgrammingError('could not receive data from server: Connection timed out\n',)
  could not receive data from server: Connection timed out
  

  Entries from /var/log/rhn/rhn_server_satellite.log contain:

  [root@satellite.example.com:~/]# tail /var/log/rhn/rhn_server_satellite.log
   File "/usr/lib/python2.6/site-packages/spacewalk/server/rhnSQL/driver_postgresql.py", line 273, in _execute_wrapper
     retval = apply(function, p, kw)
   File "/usr/lib/python2.6/site-packages/spacewalk/server/rhnSQL/sql_base.py", line 217, in _execute
     return self._execute_(args, kwargs)
   File "/usr/lib/python2.6/site-packages/spacewalk/server/rhnSQL/driver_postgresql.py", line 287, in _execute_
     self._real_cursor.execute(self.sql, params)
  ProgrammingError: could not receive data from server: Connection timed out