H3C Technologies H3C WA2600 Series WLAN Access Points - Manual (Page 70)

10-2
Fat AP
A fat AP controls and manages all associated wireless stations and bridges frames between wired and
wireless networks.
SSID
The service set identifier. A client scans all networks at first, and then selects a specific SSID to connect
to a specific wireless network.
Wireless medium
A medium that is used for transmitting frames between wireless clients. Radio frequency is used as the
wireless medium in the WLAN system.
Wireless Client Access
A wireless client access process involves three steps: active/passive scanning surrounding wireless
services, authentication, and association, as shown in Figure 10-1 .
Figure 10-1 Establish a client access
Scanning
A wireless client can get the surrounding wireless network information in two ways, passive scanning or
active scanning. With passive scanning, a wireless client gets wireless network information through
listening to Beacon frames sent by surrounding APs; with active scanning, a wireless actively sends a
probe request frame during scanning, and gets network signals by received probe response frames.
Actually, when a wireless client operates, it usually uses both passive scanning and active scanning to
get information about surrounding wireless networks.
1) Active scanning
When a wireless client operates, it periodically searches for (that is, scans) surrounding wireless
networks. Active scanning falls into two modes according to whether a specified SSID is carried in a
probe request.
z A client sends a probe request (with no SSID, which means the length of the SSID is 0.): The client
broadcasts a probe request frame on each of the supported channels to scan wireless networks.
APs that receive the probe request frame send a probe response frame. The client associates with
the AP with the strongest signal. This active scanning mode enables a client to know the available
wireless services and then access the target wireless network.