On 802.11 wireless networks, there is a set of standards that defines what frequencies and what channels these particular networks might use. These standards are defined by IEEE and are used worldwide:
- 802.11a
- 802.11b
- 802.11g
- 802.11n
The standards above are the primary standards used today, but there are also other standards in between those. There are many differences between all the standards in terms of:
- Speed
- Distance
- Channels
- Frequencies
- Country regulations
The 5 GHz frequency range is primarily used in 802.11a and 802.11n wireless networks and is not part of the standards for 802.11b or 802.11g. 802.11a uses a dynamic frequency selection (DFS) functionality that blocks interference from radar or military-type systems. In this way APs are able to coexist with other devices that might be operating on 5 GHz technology.
The 5 GHz standards use a type of multiplexing called Orthogonal Frequency Division Multiplexing (OFDM), which allows the frequency to be sent to many different channels at the same time without conflict. There are 23 non-overlapping channels that can be used, and different channels are used in different countries.
The 802.11n standard uses Multiple-Input Multiple-Output (MIMO) technology. An 802.11n-compatible access point usually contains multiple antennas because it must be capable of transmitting and receiving more than one signal at a time. You can have up to four transmits and four receives on an 802.11n network, which allows you to send and receive four data streams.
The 2.4 GHz frequency range includes a number of different wireless standards. 802.11b was one of the first standards that used this technology and it used the Direct Sequence Spread Spectrum (DSSS) method for communication. With this method, each part of the signal is put into a “chip” that is sent out across different frequencies, hopping between them to avoid interference. When using DSSS, the access points on both ends of a communication link must know what the predefined sequence is so it can listen appropriately for the traffic that comes in.
802.11b has 14 channels available and each channel is 22 MHz wide. These channels are spaced at 5 MHz intervals, thus having a certain level of overlap between them. Channels 1, 6, and 11 are used the most often because they will never conflict with each other.
The 802.11g and 802.11n standards in the 2.4 GHz frequency range also use OFDM. Those standards use the same frequencies as 802.11b, but because they use a different modulation scheme they are able to send traffic in a different way. 802.11g generally uses channels 1, 5, 9, and 13. These channels are 20 MHz wide so you should separate them to prevent any type of conflict from occurring. 802.11n uses a wide channel of 40 MHz, and you will generally use channels 3 and 11.