wpa_supplicant: how to inform AP of Sleep Mode

Holger Schurig hs4233 at mail.mn-solutions.de
Mon Oct 12 03:41:40 EDT 2009

> I think wpa_supplicant uses some type of MAC frame (for example
> for probe request, right?).


wpa_supplicant asks the kernel driver via it 
src/drivers/driver_*.c files to do the scanning.

The kernel driver will then send probe requests (if it's an 
active scan). It will also be the job of the kernel driver to 
send a NUL-packet (802.11 packet without actual data), but with 
the power-save bit set in the 802.11 flags). This will make that 
the receiving AP assumes the station is sleeping and make the AP 
buffer packets for the station (and more).

> So I believed there's a way to inform AP of the intention of
> going to sleep (modifying source code, of course)

Not from user-space. Wpa_supplicant can't send this packet 

Some WLAN cards, e.g. fullmac cards based on the libertas driver, 
have a firmware where you can't even ask the firmware to send 
such power-safe-packets.


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