
256
Figure 254
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 information by received probe response frames.
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.
•
A client sends a probe request (with the SSID
null
, that is, the SSID IE length is 0): The client
periodically sends a probe request frame on each of its supported channels to scan wireless
networks. APs that receive the probe request send a probe response, which carries the available
wireless network information. The client associates with the AP with the strongest signal. This active
scanning mode enables a client to actively get acquainted with the available wireless services and
select to access the proper wireless network as needed. The active scanning process of a wireless
client is as shown in
.
Figure 255
Active scanning (the SSID of the probe request is null, that is, no SSID information is carried)
AP 2
Client
AP 1
Prob
e req
uest
(wit
h no
SSI
D)
Probe r
equest (
with no
SSID)
Probe R
espons
e
Prob
e Re
spon
se
Содержание WA2620X-AGNP
Страница 106: ...93 Figure 90 Create a static MAC address entry ...
Страница 126: ...113 Figure 116 Information about an IGMP snooping multicast entry ...
Страница 145: ...132 Enter 10 1 1 2 for Gateway Address c Click Apply Figure 133 Configure a dynamic address pool for the DHCP server ...
Страница 187: ...174 Figure 174 Firefox web browser setting ...
Страница 219: ...206 Figure 202 Common configuration area 6 Configure the advanced parameters ...
Страница 243: ...230 Number of users Real time accounting interval in minutes 500 to 999 12 1000 15 ...
Страница 278: ...265 Figure 266 Network diagram LAN Segment ...
Страница 339: ...326 Figure 348 Configure the wireless card I ...
Страница 340: ...327 Figure 349 Configure the wireless card II ...
Страница 346: ...333 Figure 357 Configure the wireless card II ...