Difference between WLAN passive scanning vs WLAN active scanning
As we know before joining any network first client or stations or mobile stations need to find it first. In the wired world, just plugging the cable or jack will find the network. In the wireless world, this is challenging and requires identification of the compatible network before joining process can begin. This identification process of the network is referred as scanning.
Several parameters are needed in the scanning process. These parameters are specified by the user. The few of them are set as default in the WLAN client driver software.
The parameters are BSSType, BSSID, SSID, ScanType, ChannelList, ProbeDelay, MinChannelTime and MaxChannelTime.
WLAN Passive Scanning
In Passive Scanning, WLAN station moves to each channel as per channel list and waits for beacon frames. These frames are buffered and are used to decode and extract information about BSSs.
This passive scanning will save battery power as it does not need to transmit. As shown in the fig-1 WLAN client receives beacon frames from three access points and hence it will declare that it has found only three BSSs.
WLAN Active Scanning
Station plan active role in Active Scanning. On each of the channels. probe request frames are used to obtain responses from the network of choice. In active scanning station finds out network rather than waiting for network to announce its availability to all the stations.
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