H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 583)

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MU messages are sent by standard wireless devices. An MU message does not contain the channel
number; therefore, an AP cannot filter MU messages whose channel numbers are not consistent with
the AP’s operating channel or illegal packets, which is done by the location server according to a certain
algorithm and rules.
2) Collect Tag and MU messages
The working mode of an AP determines how it collects Tag and MU messages:
When the AP works in monitor mode or hybrid mode, it can locate wireless clients or other wireless
devices that are not associated with it.
When the AP works in normal mode, it can only locate wireless clients associated with it. The
wireless location system considers wireless clients associated with the AP as wireless clients, and
considers wireless clients or other wireless devices not associated with the AP as unknown
devices.
For more information about monitor mode and hybrid mode, see Security Configuration.
An AP works in normal mode when it functions as a WLAN access point. For more information, see
Wireless Service Configuration.
After the processes, the AP begins to collect Tag and MU messages.
Upon receiving Tag messages (suppose that the Tags mode has been configured on the AC, and
the location server has notified the AP to report Tag messages), the AP checks the Tag messages,
encapsulates those passing the check and reports them to the location server. The AP
encapsulates Tag messages by copying all the information (message header and payload
inclusive) except the multicast address, and adding the BSSID, channel, timestamp, data rate,
RSSI, SNR and radio mode of the radio on which the relevant Tag messages were received.
Upon receiving MU messages (suppose that the MUs mode has been configured on the AC, and
the location server has notified the AP to report MU messages), the AP checks the messages,
encapsulates those that pass the check and reports the messages to the location server. The AP
encapsulates an MU message by copying its source address, Frame Control field and Sequence
Control field, and adding the BSSID, channel, timestamp, data rate, RSSI, SNR and radio mode of
the radio on which the relevant Tag messages were received.
3) Calculate the locations of Tags or MUs
After receiving Tag and MU messages from APs, the location server uses an algorithm to calculate the
locations of the Tag and MU devices according to the RSSI, SNR, radio mode and data rate carried in
the messages, and displays the locations on the imported map. Typically, a location server can
calculate the locations as long as more than 3 APs working in monitor or hybrid report Tag or MU
messages.