I have following code.
[code]
SessionFactory sfo = new SessionFactory():
Session session = sfo.openSession();
Connection dbCon = session.connection();
connection.close();
// I am not closing session.
[/code]

Followign is Config file
[code]
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.datasource">osc_trdbcache</property>
<property name="hibernate.bytecode.use_reflection_optimizer">false</property>
<property name="hibernate.transaction.factory_class">org.hibernate.transaction.JTATransactionFactory</property>
<property name="hibernate.dialect">org.hibernate.dialect.Oracle9Dialect</property>
</session-factory>
</hibernate-configuration>
[/code]


I am not closing session, but code works fine till certain load (25 concurrent requests)
[quote]
My question is how does Hibernate work internally in this case?
[/quote]
[quote]
Is there any default session closure time out, either at Hibernate end or at Oracle end?
[/quote]

There is no timeout on Hibernate session. Lacking to do so will cause resources leak.

Usually there is no need to close connection explicitly, closing session will do this for you. I am not pretty sure about this but I think that closing connection manually will not notify the connection pool about the connection release. This may lead to incorrect behaviour too.

I can not see it in your code but watch out for transanction management.