[ACPI-sppt] question about active network sessions when hibernating

I am working with mobile clients for wireless networks, using Mobile IP (RFC 3220, 3344),
and am concerned about how to get clients to de-register before entering hibernation.  Does
the ACPI address mechanisms for notifying device drivers that a PC is entering sleep state?
If not, where should I look for this notification?
 
Also, how does the OS decide that a network device is idle?  Could this be dependent on the
semantics of the application?  In the case of a network card, there may be always be messages
arriving (e.g., broadcast messages like ARP) but that doesn't mean the card is really in use.
On the other hand, there could be an active mobile IP session without traffic for a period of 
time - only the mobile IP client would know for sure whether it was idle.  Is there any way to
deal with this?
 
Thank you,
 
Nancy Griffeth
[email protected]