802.11 operates over two major spectral bands: theISM band covering 2.4 GHz - 2.485 GHz spectrum and the 5 GHz band.
The ISM band is divided into 14 channels at different frequencies. The center frequencies are separated by 5 MHz (i.e. 2412, 2417, 2422, etc). However, the bandwidth is +/- 10 MHz. Hence, there is a significant spectral overlap on adjacent channels (i.e choosing an adjacent channel to another network is almost as bad as choosing the same channel).
Geographical location dictates which channels can be used:
- US: Channels 1-11
- Europe: Channels 1-13
- Japan: Channels 1-14
Setting The Channel:
The Access Point (AP) administrator chooses a channel for a specific AP. Interferenceis possible. The channel selected can be the same as that chosen by a neighboring AP!
In the US, channels 1, 6, and 11 are non-overlapping (at the -3 dB points), so these are typically selected for APs.
In Europe, channels 3, 8, and 13 are typically used.
