Perhaps you should ask your firewall manufacturer or read your firewall manual?
Thanks for replying.
Is there a way to configure jboss or the clients connecting to jboss ? (with some kind of timeout setting? )
You can't configure JBoss Messaging to prevent your firewall closing connections!
If your firewall decides to close connections then no application can stop it - if it could it would be a pretty useless firewall (think of the exploits).
You need to read your firewall manual and find out how to prevent it from closing connections.