What is dual band in WLAN?

What is meant by dual band in WLAN?
You'll hear a lot in the press about the different prominent wireless technologies - some people will be preaching 802.11b, some 802.11a and the others will most likely have moved to trying to sell 802.11g (even though its not yet ratified by the IEEE.) However, what most people don't actually talk about is the specific band (frequency ranges) that the devices operate in.

Some time ago the governments around the world put aside a few parts of the spectrum, termed ISM bands, to be used for Industrial, Scientific and Medical purposes. Essentially they created parts of the Radio Frequency (RF) spectrum that people can utilize without requiring a RF Spectrum License from the relevant authority (the classic example is the use of a microwave oven - it produces RF signals in the 2.4-2.5 GHz band as a by-product of its operations but owners are not required to purchase a RF Spectrum License in order to buy or use one.)

Currently there are two predominant ISM bands in use for 802.11 wireless networking; the 2.4 - 2.5 GHz (used for 802.11b and 802.11g) and the 5.725 - 5.875 GHz range (used for 802.11a) and as such any device looking to operate as a dual-band device should be capable of operating in both of the aforementioned bands. Realistically speaking a dual band device would almost certainly support 802.11a and 802.11b as opposed to 802.11g (due to the lack of ratification.)

Within each band there are a number of channels that can be used by wireless devices. Depending on your location there are between 1 and 14 channels that can be used at any one time within the 2.4 - 2.5 GHz band (the American FCC standards allow for 11 channels whilst the European ETSI standards allows for 14.) The 5.725 - 5.875 GHz currently provides for 8 non-overlapping channels.