about 802.11 scan and probe request

about 802.11 scan and probe request

[belle.shi]

dear all,
   is there anyone who read the standard "Part 11: Wireless LAN Medium
Access Control (MAC) and Physical Layer (PHY) Specifications" ?
   and i spend two month to read the stardard, and i read a few code of 
wpa_suppliant and
wpa_gui,there is one question: the scan have two mode:active or 
passive,but when i run
the wpa_gui, there is only scan button, in the standard the scan 
request is like
MLME-SCAN.request (
                 BSSType,
                 BSSID,
                 SSID,
                 ScanType,
                 ProbeDelay,
                 ChannelList,
                 MinChannelTime,
                 MaxChannelTime
                 )
but there are only three MAC frame formats:data frame, control frame 
and Management
frame, and there is no scan frame, there is only a Probe Request frame, 
    so i am
stumped, what's the relationship between MLME-SCAN.request and Probe 
Request frame, is
the MLME-SCAN.request and Probe Request frame only in different layer? 
but the items is
also different, the MLME-SCAN.request have:(
BSSType, BSSID, SSID,  ScanType, ProbeDelay,  ChannelList,  
MinChannelTime,   MaxChannelTime), but the  Probe Request frame body 
only have two parts:  SSID
and Supported rates.     and in my view, i think the active scan is to 
send Probe Request
frame, and the passive scan to receive the beacon frame, is it right?
    thanks very much for advance!!
belle

Re: about 802.11 scan and probe request

[Kalle Valo]

belle.shi@yy.com writes:

> there is one question: the scan have two mode:active or passive,but
> when i run the wpa_gui, there is only scan button

Passive scan is so slow that we want to use active scan always when
possible. No need to confuse users about this, so one scan button is
enough.

> i think the active scan is to send Probe Request frame, and the
> passive scan to receive the beacon frame, is it right?

Correct.

-- 
Kalle Valo