How to increase inactive session timeout (BI Pub 11.1.1.5)

We have installed BI Pub 11.1.1.5.

End users access BI Pub by the Web application xmlpserver : http://machine:****/xmlpserver

Inactive session timeout is currently (default value) 15 minutes or 16 minutes.
End user session is closed.

We would like increasing this timeout to 2 hours.
No explicit parameters in properties file, nor in MBean (WebLogic Server / server bi_server1).

Thanks for help.

Regards,
Laurent 
This is handled by the WLS server not BIP.

See these docs:

http://download.oracle.com/docs/cd/E21764_01/doc.1111/e14772/weblogic_server_issues.htm#ASRSS2083
http://download.oracle.com/docs/cd/E21764_01/core.1111/e10108/webcenter.htm#ASPER183

If this does not work, please log an SR with WLS Support to get assistance.