This figure illustrates an Oracle Application Server configuration using port tunneling. The iaspt daemon, a standalone component, acts as a communication concentrator for connections between Oracle HTTP Server, which is guarded by firewalls on both sides, and OC4J.

Oracle HTTP Server does not connect directly to OC4J. Instead, it connects to the iaspt daemon which then forwards communication on to OC4J. Each iaspt daemon routes requests to multiple OC4J instances. By doing this concentration of connections, only one port is opened per port tunneling on the internal firewall, instead of one port per OC4J instance.