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Wireless Channel Hopping

6 Jun 2011

Ever wondered how your devices like your laptop get the list of wireless networks available?

 

First of all, you have to understand that at any point of time, a wireless card can only listen to one specific wireless channel at one point in time. This means that if your access point is on channel 6, it would be likely that your wireless card on your laptop could only be listening to channel 6 and ignoring the other wireless channels.

 

How would you then get all the list of wireless networks then?

 

Firstly, when the signal strength from an access point is weak or when your wireless card decides to channel hop, it would send a NULL function data frame with the Power Management bit in the frame control field of the MAC address header set to “1” to inform the access point to buffer frames intended for the station. Once the station has returned to it associated channel, the channel sends another NULL Function data frame with the Power Management bit set to “0” to inform the access point to begin forwarding frames again. This is to prevent frames from being lost while the laptop’s wireless card is listening to other different channels for alternate access point.

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