Looking Back At The 802.11 Standard – Wi-Fi Basics
The IEEE (Institute of Electrical and Electronics Engineers), who write the 802.11 standards, is one of the names you will see most in any networking arena. They create and vet the standards, and, along with chipmakers and vendors, bring these standards to specifications and to the market. Another name to know is the Wi-Fi Alliance, a group that certifies that Wi-Fi gear will interoperate. Vendors are not required to be certified by the Wi-Fi Alliance, but you absolutely must make sure that any vendor you are considering has gone through that process, just to ensure that there are no surprises.
With the advent of the IEEE 802.11n standard, which started in 2007, wireless LANs have gone from isolated, convenience-oriented networks to the de facto access method in many organizations. This shift has happened hand in hand with the development of cost-effective mobile computing devices. Because the vast majority of these devices, including smartphones, laptops, and e-readers don’t even have an Ethernet port for wired connectivity, Wi-Fi is mandatory for their use. With the approval of the 802.11n standard, Wi-Fi networking went mainstream.
Wi-Fi runs on two different low-power radio bands: the 2.4GHz band and the higher-frequency 5GHz band. Many other non-Wi-Fi devices run on the 2.4GHz band, including things like microwaves and older portable phones, so there is more interference there. The 2.4GHz band also tends to extend farther than the higher-frequency 5GHz band, making the interference more apparent in dense environments. The 5GHz band has more channels available, and does not extend quite as far as the 2.4GHz band, but some legacy clients may not support it.
The 802.11n standard introduced some important technological elements; including the concept of an antenna technology called MIMO, which stands for Multiple In Multiple Out.
MIMO allows multiple antennas in both the client device and the access point to communicate simultaneously, which dramatically boosts throughput. While the following few sentences may sound like technical mumbo jumbo, they will help you understand how to read an access point (AP) datasheet and some of the basic experiences that you might have while on a Wi-Fi connection.
When you look at AP datasheets, you will see a designation showing [X] x [Y] : Z. In the example shown here, the designation is 3×3:3. This means that the access point you are looking at has three transmit antennas and three receive antennas, which may be included inside the body of the AP. The last number, behind the colon, stands for spatial streams. Spatial streams enable the AP to split the outgoing signal into Z number of pieces, and send them at the same time; they can also send the same signal Z times simultaneously, for greater accuracy. In this datasheet example, the AP has three spatial streams. The most important thing to know about MIMO, however, is that the access point can only use the same number of antennas and spatial streams as the client device. Many client devices, such as smartphones, only support one receive antenna, one transmit antenna, and one spatial stream. This is because the use of multiple antennas takes up a lot of battery life. Therefore, you must take care to test any Wi-Fi deployment with identical clients in identical placement.
REMEMBER: Test for speed in your environment. It is not possible to reach the theoretical maximum output of a Wi-Fi device, although some vendors will actually cite those numbers as their throughput.
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