Hello,
connections have timeouts, so you probably want to use a connection pool.
Most applications servers have good connection pools, but you should use a DataSource in that case and not encode your connection options in your hibernate configuration.
If you don't use an application server you may want to configure C3p0,
look at hibernate docs
http://www.hibernate.org/214.html
or the c3p0 website
http://sourceforge.net/projects/c3p0
in the c3p0 package you'll find a good explanation for alla parameters, and some additional info especially for Oracle.
Actually if you are using Tomcat it would be much easier to use JBoss instead.