H3C Technologies H3C MSR 50 - Manual (Page 20)

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2. Passive scanning
Passive scanning is used by clients to discover surrounding wireless networks through listening to
the beacon frames periodically sent by an AP. All APs providing wireless services periodically
send beacons frames, so that wireless clients can periodically listen to beacon frames on the
supported channels to get information about surrounding wireless networks and connect to an AP.
Passive scanning is used by a client when it wants to save battery power. Typically, VoIP clients
adopt the passive scanning mode. The passive scanning process is as shown in Figure 4 .
Figure 4 Passive scanning
Authentication
To secure wireless links, the wireless clients must be authenticated before accessing the AP, and only
wireless clients passing the authentication can be associated with the AP. 802.11 links define two
authentication mechanisms: open system authentication and shared key authentication.
For more information about the two authentication mechanisms, see "Configuring WLAN security."
Association
A client that wants to access a wireless network through an AP must be associated with that AP. Once the
client chooses a compatible network with a specified SSID and passes the link authentication to an AP,
it sends an association request frame to the AP. The AP detects the capability information carried in the
association request frame, determines the capability supported by the wireless client, and sends an
association response to the client to notify the client of the association result. Usually, a client can
associate with only one AP at a time, and an association process is always initiated by the client.
Workgroup bridge mode overview
The workgroup bridge mode enables an AP to associate with another AP as a wireless client.
As shown in
Figure 5 , to provide wireless connectivity for the PCs and printer, you can connect them to
an AP through a hub or a switch and configure the AP as a workgroup bridge. The PCs and printer
access the network through the workgroup bridge.