Routing Notifications in SAP 6.5

As SAP Routing Rules are upgraded with Routing Notifications in SAP 6.5 adapter, When we try to add a Routing Notification two documents “RoutingNotificationRequestDocument” & “RoutingNotificationReplyDocument” is getting created automatically. What is the use of those documents? Is it used internally?

Also what is the difference b/w ALE Listener notification & Routing Notification?