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I'm in training this week with an RFID location tracking company (over WiFi) and they claim to be able to support a location tracking method for devices other than their tags using their location receivers. (kinda like an AP that mainly just listens).

Here's how they're saying it works. They talk about the RTS/CTS behavior in 802.11 and state the following:

Finding Mobile Units:
"...In active mode, Access Points or AeroScout Location Receivers transmit a signal to the mobile unit and wait for its reply in order to obtain its location. The Access Point or Location Receiver sends a location request in the form of an RTS (Request to Send) signal and the Mobile Unit responds with a CTS (Clear to Send).

...A Mobile Unit is searched and located by its MAC address. The search is
carried out over a specific Access Point/Location Receiver channel or by
scanning multiple channels with the Location Receivers. In the case of
Location Receivers, the RTS is sent through the LRs whose Mobile Unit
Location Finding Trigger parameter has been enabled (see page 40). Other
LRs participate only in the Mobile Unit positioning process, but not in the
initial finding of the mobile unit on the specific channel.

The signal acknowledgment timeouts, the channels to scan and other general mobile unit settings are defined in System Parameters. See page 28."

This is interesting. I was thinking 'BS' when I heard this because as some clients might behave this way others may not. Keep in mind here, we're talking about clients that are NOT associated. Clients that are associated are nother issue. I have read nothing that I recall in the standards that have talked about this.

I therefore did a test. My laptop is Windows XP Pro using (for the test) an internal Intel 2915ABG and a Cisco CB21AG with the Funk Odyssey client (v4.51). I sniffed using AiroPeek with the Cisco card and, using their system, searched for the MAC of my Intel card. I saw the LRs above actively scanning for it sending an RTS to the Intel card and, as you also might have guessed, NO response from my Intel card. I repeated this several times and tried other clients (laptops next to me) and some worked, while others did not. (~75% of the time it worked)

Perhaps different supplicants shape this behavior differently. I find this really interesting. Can any of you shed light on this?

Shawn