Oracle cannot connect remotely for important reasons, even if the firewall is open 1521 port, but the return packet may be a random port, so it is still possible to be blocked by the firewall.
Workaround:
Add a String value in the registry as follows. can be resolved
It takes two days to find a way
[HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOME0] "Use_shared_socket" = "TRUE"
Ora-12516:tns:listener could not find available handler with matching protocol stack conn/as SYSDBA
Select COUNT (*) from v$session show parameter processes
modifying processes and Sessions values
Sql> alter system set processes=1000 Scope=spfile;
The system has changed.
Sql> alter system set sessions=1000 Scope=spfile;
The system has changed.
Restart database is in effect
Ora-03135:connection lost contact Sqlnet. Expire_time = 100
2011-04-21 thread attached Oracle's approach