IEEE 802.11x

Definition - What does IEEE 802.11x mean?

802.11x is generic term to refer to the IEEE 802.11 standard for defining communication over a wireless LAN (WLAN). 802.11, commonly known as Wi-Fi, specifies an over-the-air interface between a wireless client and a base station or between two wireless clients. These standards are used to implement WLAN communication in 2.4, 3.6 and 5 GHz frequency bands.

The term is not officially used or defined. Rather, it refers to the common flavors of Wi-Fi, most notably 802.11a, 802.11b, 802.11g, and 802.11n.

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Techopedia explains IEEE 802.11x

It is common to refer to 802.11 as the set of standards, but it is slightly more accurate to refer to it as the 802.11 family or 802.11x as there is technically only one standard, which is currently 802.11-2007. The rest of the "family" are technically amendments. Some of the better known amendments are:

802.11-1997: The original standard released in 1997 provided 1-2 Mbps transmission speed in the 2.4 GHz band using Frequency Hoping Spread Spectrum (FHSS) or Direct Sequence Spread Spectrum (DSSS). It is currently obsolete.
802.11a: Provides a transmission speed of up to 54 Mbps in the 5 GHz band using Orthogonal Frequency-Division Multiplexing (OFDM).
802.11b: Works in the 2.4 GHz band and can provide up to 11 Mbps speed with a fallback rate to 5.5, 2 and 1 Mbps. 802.11b only uses DSSS.
802.11g: Provides a maximum speed of 54 Mbps in the 2.4 GHz band. 802.11g uses OFDM and DSSS and is backwards compatible with 802.11b.
802.11n: Provides up to 150 Mbps throughput using spatial multiplexing. It uses the both 2.4 and 5 GHz band.