40 MHz Channelization
When 40 MHz channels are used in 802.11n networks, two 20 MHz channels are bonded together. The two 20 Mhz channels are designated as primary and secondary and are designated by two fields: (Primary, Secondary) where the Primary is the number of the primary channel and the Secondary is a positive or negative integer indicating whether the secondary channel is one channel above or one channel below the primary channel). 40 MHz channels MUST consist of immediately adjacent 20 MHz channels allowed within the regulatory domain.
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