The ISM band is divided into 14 channels at different frequencies. Centre frequencies are separated by 5MHz (i.e. 2412, 2417, 2422 etc) however the bandwidth is +/- 10MHz, so there is 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. Interference is possible. The channel selected can be same as that chosen by neighboring AP!
In the US, channels 1, 6, 11 are non-overlapping (at the -3dB points) so these are typically selected for APs.
In Europe, channels 3, 8, 13 are typically used.