Integration

I witted a class implements interface HttpSessionBindingListener to write session timeout information into DB using method valueunbound() when session timeout.
The programs runs in apache/Jserv, and the oracle application version is 11.5.10.2.
The profile ICX: Session Timeout value is 30min, and parameter session.timeout in zone.properties is 30min too, but when timeout(30min later) , method valueunbound() was not invoked.
When the value of profile ICX: Session Timeout is longer than the value of parameter session.timeout in zone.properties, method valueunbound() was invoked,
and writed log into DB.
Why the phenomenon happened, and where can I set the session timeout value except of profile ICX: Session Timeout and parameter session.timeout in zone.properties ? Is there any differencies between ICX: Session Timeout and session.timeout ?