Most modern 802.11n and 802.11ac enterprise grade access points (APs) are what are known as a dual-band access point. That is to say that the access point can transmit and receive in two separate bands approved by the FCC and other regulatory agencies around the world.
Several years ago, you’d see dual-band access points that had separate antennas for their 2.4 GHz and 5 GHz radios. These days, however, even the antennas are dual-band, meaning that a single antenna connection is servicing both a 2.4 and 5 GHz radio in a single AP.
The first band is 2.4GHz
This has traditionally been used by a wide range of devices such as Bluetooth, cordless phones, and wireless baby monitors, in addition to wireless access points. The benefit of 2.4GHz is that it is a lower frequency than 5 GHz, and thus penetrates most obstructions (such as walls) better. The signal can also propagate farther.
However, radio band sees more interference and is so narrow that only 3 non-overlapping 20MHz channels (1, 6 and 11) exist for 2.4GHz in the US.
The second band is 5 GHz
In the US, this is actually four bands in the 5 to 5.9GHz range. These four bands have different levels of support among wired devices and different maximum power requirements set by the FCC, in additional to different rules for indoor and outdoor transmission power levels. Additionally, because these bands use a higher frequency, their signals have a more difficult time penetrating solid obstructions.
However, 5 GHz provides us with significantly more usable channels, and the new 802.11ac wireless standard only uses the 5 GHz band. While commercial 2.4 GHz APs are limited to 20 MHz wide channels, we can use 40 MHz or 80 MHz wide channels in 5 GHz, essentially doubling or quadrupling our throughput in the 5 GHz band.
While a dual-band access point will be able to support 2.4 GHz and 5 GHz, it will only be able to take advantage of the channels supported by the endpoint device trying to connect to it. In some cases this will be a 2.4 GHz only device, while in other cases this may be a dual-band device that cannot support all of the available 5 GHz channels. While most newer devices are dual-band devices with good support for most 5 GHz channels, Amazon’s most recent member of the Kindle Fire family, as of this writing, is the HD 6, a 2.4 GHz only device, presumably to keep the cost of the device down.
No matter how robust a dual-band wireless network is, none of the benefits of 802.11ac or 5 GHz channel availability can be realized for users who are using a 2.4 GHz only device. However, dual-band access points that are saturated in the 2.4 GHz band based on the limited channel size, channel noise, and limited throughput of 2.4 GHz speeds still have the ability to leverage wider channels, higher data rates, and cleaner channels for devices connecting at 5 GHz.
In a well designed wireless network, the endpoint devices are the weakest link; but, dual-band access points help ensure we’re leveraging available wireless bandwidth in both wireless bands to support the demands on the wireless network.