IEEE 802.11


IEEE 802.11 is part of the IEEE 802 set of local area network protocols, and specifies the set of media access control and physical layer protocols for implementing wireless local area network Wi-Fi computer communication in various frequencies, including but not limited to 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz frequency bands.
They are the world's most widely used wireless computer networking standards, used in most home and office networks to allow laptops, printers, and smartphones to talk to each other and access the Internet without connecting wires. They are created and maintained by the Institute of Electrical and Electronics Engineers LAN/MAN Standards Committee. The base version of the standard was released in 1997, and has had subsequent amendments. The standard and amendments provide the basis for wireless network products using the Wi-Fi brand. While each amendment is officially revoked when it is incorporated in the latest version of the standard, the corporate world tends to market to the revisions because they concisely denote capabilities of their products. As a result, in the marketplace, each revision tends to become its own standard.
The protocols are typically used in conjunction with IEEE 802.2, and are designed to interwork seamlessly with Ethernet, and are very often used to carry Internet Protocol traffic.
Although IEEE 802.11 specifications list channels that might be used, the radio frequency spectrum availability allowed varies significantly by regulatory domain.

General description

The 802.11 family consists of a series of half-duplex over-the-air modulation techniques that use the same basic protocol. The 802.11 protocol family employs carrier-sense multiple access with collision avoidance whereby equipment listens to a channel for other users before transmitting each packet.
802.11-1997 was the first wireless networking standard in the family, but 802.11b was the first widely accepted one, followed by 802.11a, 802.11g, 802.11n, and 802.11ac. Other standards in the family are service amendments that are used to extend the current scope of the existing standard, which may also include corrections to a previous specification.
802.11b and 802.11g use the 2.4 GHz ISM band, operating in the United States under Part 15 of the U.S. Federal Communications Commission Rules and Regulations; 802.11n can also use that band. Because of this choice of frequency band, 802.11b/g/n equipment may occasionally suffer interference in the 2.4 GHz band from microwave ovens, cordless telephones, and Bluetooth devices etc. 802.11b and 802.11g control their interference and susceptibility to interference by using direct-sequence spread spectrum and orthogonal frequency-division multiplexing signaling methods, respectively.
802.11a uses the 5 GHz U-NII band, which, for much of the world, offers at least 23 non-overlapping 20 MHz-wide channels rather than the 2.4 GHz ISM frequency band offering only three non-overlapping 20 MHz-wide channels, where other adjacent channels overlap—see list of WLAN channels. Better or worse performance with higher or lower frequencies may be realized, depending on the environment. 802.11n can use either the 2.4 GHz or 5 GHz band; 802.11ac uses only the 5 GHz band.
The segment of the radio frequency spectrum used by 802.11 varies between countries. In the US, 802.11a and 802.11g devices may be operated without a license, as allowed in Part 15 of the FCC Rules and Regulations. Frequencies used by channels one through six of 802.11b and 802.11g fall within the 2.4 GHz amateur radio band. Licensed amateur radio operators may operate 802.11b/g devices under Part 97 of the FCC Rules and Regulations, allowing increased power output but not commercial content or encryption.
In 2018, the Wi-Fi Alliance began using a consumer-friendly generation numbering scheme for the publicly used 802.11 protocols. Wi-Fi generations 1–6 refer to the 802.11b, 802.11a, 802.11g, 802.11n, 802.11ac, and 802.11ax protocols, in that order.

History

802.11 technology has its origins in a 1985 ruling by the U.S. Federal Communications Commission that released the ISM band for unlicensed use.
In 1991 NCR Corporation/AT&T invented a precursor to 802.11 in Nieuwegein, the Netherlands. The inventors initially intended to use the technology for cashier systems. The first wireless products were brought to the market under the name WaveLAN with raw data rates of 1 Mbit/s and 2 Mbit/s.
Vic Hayes, who held the chair of IEEE 802.11 for 10 years, and has been called the "father of Wi-Fi", was involved in designing the initial 802.11b and 802.11a standards within the IEEE.
In 1999, the Wi-Fi Alliance was formed as a trade association to hold the Wi-Fi trademark under which most products are sold.
The major commercial breakthrough came with Apple Inc. adopting Wi-Fi for their iBook series of laptops in 1999. It was the first mass consumer product to offer Wi-Fi network connectivity, which was then branded by Apple as AirPort. One year later IBM followed with its ThinkPad 1300 series in 2000.

Protocol

802.11-1997 (802.11 legacy)

The original version of the standard IEEE 802.11 was released in 1997 and clarified in 1999, but is now obsolete. It specified two net bit rates of 1 or 2 megabits per second, plus forward error correction code. It specified three alternative physical layer technologies: diffuse infrared operating at 1 Mbit/s; frequency-hopping spread spectrum operating at 1 Mbit/s or 2 Mbit/s; and direct-sequence spread spectrum operating at 1 Mbit/s or 2 Mbit/s. The latter two radio technologies used microwave transmission over the Industrial Scientific Medical frequency band at 2.4 GHz. Some earlier WLAN technologies used lower frequencies, such as the U.S. 900 MHz ISM band.
Legacy 802.11 with direct-sequence spread spectrum was rapidly supplanted and popularized by 802.11b.

802.11a (OFDM waveform)

802.11a, published in 1999, uses the same data link layer protocol and frame format as the original standard, but an OFDM based air interface. It operates in the 5 GHz band with a maximum net data rate of 54 Mbit/s, plus error correction code, which yields realistic net achievable throughput in the mid-20 Mbit/s. It has seen widespread worldwide implementation, particularly within the corporate workspace.
Since the 2.4 GHz band is heavily used to the point of being crowded, using the relatively unused 5 GHz band gives 802.11a a significant advantage. However, this high carrier frequency also brings a disadvantage: the effective overall range of 802.11a is less than that of 802.11b/g. In theory, 802.11a signals are absorbed more readily by walls and other solid objects in their path due to their smaller wavelength, and, as a result, cannot penetrate as far as those of 802.11b. In practice, 802.11b typically has a higher range at low speeds. 802.11a also suffers from interference, but locally there may be fewer signals to interfere with, resulting in less interference and better throughput.

802.11b

The 802.11b standard has a maximum raw data rate of 11 Mbit/s, and uses the same media access method defined in the original standard. 802.11b products appeared on the market in early 2000, since 802.11b is a direct extension of the modulation technique defined in the original standard. The dramatic increase in throughput of 802.11b along with simultaneous substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.
Devices using 802.11b experience interference from other products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include microwave ovens, Bluetooth devices, baby monitors, cordless telephones, and some amateur radio equipment. As unlicensed intentional radiators in this ISM band, they must not interfere with and must tolerate interference from primary or secondary allocations of this band, such as amateur radio.

802.11g

In June 2003, a third modulation standard was ratified: 802.11g. This works in the 2.4 GHz band, but uses the same OFDM based transmission scheme as 802.11a. It operates at a maximum physical layer bit rate of 54 Mbit/s exclusive of forward error correction codes, or about 22 Mbit/s average throughput. 802.11g hardware is fully backward compatible with 802.11b hardware, and therefore is encumbered with legacy issues that reduce throughput by ~21% when compared to 802.11a.
The then-proposed 802.11g standard was rapidly adopted in the market starting in January 2003, well before ratification, due to the desire for higher data rates as well as reductions in manufacturing costs. By summer 2003, most dual-band 802.11a/b products became dual-band/tri-mode, supporting a and b/g in a single mobile adapter card or access point. Details of making b and g work well together occupied much of the lingering technical process; in an 802.11g network, however, activity of an 802.11b participant will reduce the data rate of the overall 802.11g network.
Like 802.11b, 802.11g devices also suffer interference from other products operating in the 2.4 GHz band, for example wireless keyboards.

802.11-2007

In 2003, task group TGma was authorized to "roll up" many of the amendments to the 1999 version of the 802.11 standard. REVma or 802.11ma, as it was called, created a single document that merged 8 amendments with the base standard. Upon approval on 8 March 2007, 802.11REVma was renamed to the then-current base standard IEEE 802.11-2007.

802.11n

802.11n is an amendment that improves upon the previous 802.11 standards, that had the first draft of certification published in 2006. The 802.11n standard was retroactively labelled as Wi-Fi 4 by the Wi-Fi Alliance. The standard added support for multiple-input multiple-output antennas. 802.11n operates on both the 2.4 GHz and the 5 GHz bands. Support for 5 GHz bands is optional. Its net data rate ranges from 54 Mbit/s to 600 Mbit/s. The IEEE has approved the amendment, and it was published in October 2009. Prior to the final ratification, enterprises were already migrating to 802.11n networks based on the Wi-Fi Alliance's certification of products conforming to a 2007 draft of the 802.11n proposal.

802.11-2012

In May 2007, task group TGmb was authorized to "roll up" many of the amendments to the 2007 version of the 802.11 standard. REVmb or 802.11mb, as it was called, created a single document that merged ten amendments with the 2007 base standard. In addition much cleanup was done, including a reordering of many of the clauses. Upon publication on 29 March 2012, the new standard was referred to as IEEE 802.11-2012.

802.11ac

IEEE 802.11ac-2013 is an amendment to IEEE 802.11, published in December 2013, that builds on 802.11n. The 802.11ac standard was retroactively labelled as Wi-Fi 5 by Wi-Fi Alliance. Changes compared to 802.11n include wider channels in the 5 GHz band, more spatial streams, higher-order modulation, and the addition of Multi-user MIMO. The Wi-Fi Alliance separated the introduction of ac wireless products into two phases, named "Wave 1" and "Wave 2". From mid-2013, the alliance started certifying Wave 1 802.11ac products shipped by manufacturers, based on the IEEE 802.11ac Draft 3.0. In 2016 Wi-Fi Alliance introduced the Wave 2 certification, to provide higher bandwidth and capacity than Wave 1 products. Wave 2 products include additional features like MU-MIMO, 160 MHz channel width support, support for more 5 GHz channels, and four spatial streams.

802.11ad

IEEE 802.11ad is an amendment that defines a new physical layer for 802.11 networks to operate in the 60 GHz millimeter wave spectrum. This frequency band has significantly different propagation characteristics than the 2.4 GHz and 5 GHz bands where Wi-Fi networks operate. Products implementing the 802.11ad standard are being brought to market under the WiGig brand name. The certification program is now being developed by the Wi-Fi Alliance instead of the now defunct Wireless Gigabit Alliance. The peak transmission rate of 802.11ad is 7 Gbit/s.
IEEE 802.11ad is a protocol used for very high data rates and for short range communication.
TP-Link announced the world's first 802.11ad router in January 2016.
The WiGig standard is not too well known, although it was announced in 2009 and added to the IEEE 802.11 family in December 2012.

802.11af

IEEE 802.11af, also referred to as "White-Fi" and "Super Wi-Fi", is an amendment, approved in February 2014, that allows WLAN operation in TV white space spectrum in the VHF and UHF bands between 54 and 790 MHz. It uses cognitive radio technology to transmit on unused TV channels, with the standard taking measures to limit interference for primary users, such as analog TV, digital TV, and wireless microphones. Access points and stations determine their position using a satellite positioning system such as GPS, and use the Internet to query a geolocation database provided by a regional regulatory agency to discover what frequency channels are available for use at a given time and position. The physical layer uses OFDM and is based on 802.11ac. The propagation path loss as well as the attenuation by materials such as brick and concrete is lower in the UHF and VHF bands than in the 2.4 GHz and 5 GHz bands, which increases the possible range. The frequency channels are 6 to 8 MHz wide, depending on the regulatory domain. Up to four channels may be bonded in either one or two contiguous blocks. MIMO operation is possible with up to four streams used for either space–time block code or multi-user operation. The achievable data rate per spatial stream is 26.7 Mbit/s for 6 and 7 MHz channels, and 35.6 Mbit/s for 8 MHz channels. With four spatial streams and four bonded channels, the maximum data rate is 426.7 Mbit/s for 6 and 7 MHz channels and 568.9 Mbit/s for 8 MHz channels.

802.11-2016

IEEE 802.11-2016 which was known as IEEE 802.11 REVmc, is a revision based on IEEE 802.11-2012, incorporating 5 amendments. In addition, existing MAC and PHY functions have been enhanced and obsolete features were removed or marked for removal. Some clauses and annexes have been renumbered.

802.11ah

IEEE 802.11ah, published in 2017, defines a WLAN system operating at sub-1 GHz license-exempt bands. Due to the favorable propagation characteristics of the low frequency spectra, 802.11ah can provide improved transmission range compared with the conventional 802.11 WLANs operating in the 2.4 GHz and 5 GHz bands. 802.11ah can be used for various purposes including large scale sensor networks, extended range hotspot, and outdoor Wi-Fi for cellular traffic offloading, whereas the available bandwidth is relatively narrow. The protocol intends consumption to be competitive with low power Bluetooth, at a much wider range.

802.11ai

IEEE 802.11ai is an amendment to the 802.11 standard that added new mechanisms for a faster initial link setup time.

802.11aj

IEEE 802.11aj is a rebanding of 802.11ad for use in the 45 GHz unlicensed spectrum available in some regions of the world.
Alternatively known as China Millimeter Wave.

802.11aq

IEEE 802.11aq is an amendment to the 802.11 standard that will enable pre-association discovery of services. This extends some of the mechanisms in 802.11u that enabled device discovery to further discover the services running on a device, or provided by a network.

802.11ax

IEEE 802.11ax is the successor to 802.11ac, and will increase the efficiency of WLAN networks. This project has the goal of providing 4x the throughput of 802.11ac at the user layer, having just 37% higher nominal data rates at the PHY layer. The 802.11ax standard is expected to become an official IEEE specification in September 2020. In the previous amendment of 802.11, Multi-User MIMO has been introduced, which is a spatial multiplexing technique. MU-MIMO allows the Access Point to form beams towards each Client, while transmitting information simultaneously. By doing so, the interference between Clients is reduced, and the overall throughput is increased, since multiple Clients can receive data at the same time. With 802.11ax, a similar multiplexing is introduced in the frequency domain, namely OFDMA. With this technique, multiple Clients are assigned with different Resource Units in the available spectrum. By doing so, an 80 MHz channel can be split into multiple Resource Units, so that multiple Clients receive different type of data over the same spectrum, simultaneously. In order to have enough subcarriers to support the requirements of OFDMA, four times as many subcarriers are needed than by the 802.11ac standard. In other words, for 20, 40, 80 and 160 MHz channels, there are 64, 128, 256 and 512 subcarriers in the 802.11ac standard, but 256, 512, 1024 and 2048 subcarriers in the 802.11ax standard. Since the available bandwidths have not changed and the number of subcarriers increases by a factor of 4, the subcarrier spacing is reduced by the same factor, which introduces 4 times longer OFDM symbols: for 802.11ac the duration of an OFDM symbol is 3.2 microseconds, and for 802.11ax it is 12.8 microseconds.

802.11ay

IEEE 802.11ay is a standard that is being developed. It is an amendment that defines a new physical layer for 802.11 networks to operate in the 60 GHz millimeter wave spectrum. It will be an extension of the existing 11ad, aimed to extend the throughput, range and use-cases. The main use-cases include: indoor operation, out-door back-haul and short range communications. The peak transmission rate of 802.11ay is 20 Gbit/s. The main extensions include: channel bonding, MIMO and higher modulation schemes.

802.11be

IEEE 802.11be Extremely High Throughput is the potential next amendment of the 802.11 IEEE standard. It will build upon 802.11ax, focusing on WLAN indoor and outdoor operation with stationary and pedestrian speeds in the 2.4 GHz, 5 GHz, and 6 GHz frequency bands.

Common misunderstandings about achievable throughput

Across all variations of 802.11, maximum achievable throughputs are given either based on measurements under ideal conditions or in the layer-2 data rates. However, this does not apply to typical deployments in which data is being transferred between two endpoints, of which at least one is typically connected to a wired infrastructure and the other endpoint is connected to an infrastructure via a wireless link.
application specific performance envelope 2.4 GHz band, with 802.11n with 40MHz
This means that, typically, data frames pass an 802.11 medium, and are being converted to 802.3 or vice versa. Due to the difference in the frame lengths of these two media, the application's packet size determines the speed of the data transfer. This means applications that use small packets create dataflows with high-overhead traffic. Other factors that contribute to the overall application data rate are the speed with which the application transmits the packets and, of course, the energy with which the wireless signal is received. The latter is determined by distance and by the configured output power of the communicating devices.
The same references apply to the attached graphs that show measurements of UDP throughput. Each represents an average throughput of 25 measurements. Each is with a specific packet size and with a specific data rate. Markers for traffic profiles of common applications are included as well. These figures assume there are no packet errors, which if occurring will lower transmission rate further.

Channels and frequencies

802.11b, 802.11g, and 802.11n-2.4 utilize the spectrum, one of the ISM bands. 802.11a, 802.11n and 802.11ac use the more heavily regulated band. These are commonly referred to as the "2.4 GHz and 5 GHz bands" in most sales literature. Each spectrum is sub-divided into channels with a center frequency and bandwidth, analogous to the way radio and TV broadcast bands are sub-divided.
The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, beginning with channel 1, which is centered on 2.412 GHz. The latter channels have additional restrictions or are unavailable for use in some regulatory domains.
channels in the 2.4 GHz band
The channel numbering of the spectrum is less intuitive due to the differences in regulations between countries. These are discussed in greater detail on the list of WLAN channels.

Channel spacing within the 2.4 GHz band

In addition to specifying the channel center frequency, 802.11 also specifies a spectral mask defining the permitted power distribution across each channel. The mask requires the signal be attenuated a minimum of 20 dB from its peak amplitude at ±11 MHz from the centre frequency, the point at which a channel is effectively 22 MHz wide. One consequence is that stations can use only every fourth or fifth channel without overlap.
Availability of channels is regulated by country, constrained in part by how each country allocates radio spectrum to various services. At one extreme, Japan permits the use of all 14 channels for 802.11b, and for 802.11g/n-2.4. Other countries such as Spain initially allowed only channels 10 and 11, and France allowed only 10, 11, 12, and 13; however, Europe now allow channels 1 through 13. North America and some Central and South American countries allow only
Since the spectral mask defines only power output restrictions up to ±11 MHz from the center frequency to be attenuated by −50 dBr, it is often assumed that the energy of the channel extends no further than these limits. It is more correct to say that, given the separation between channels, the overlapping signal on any channel should be sufficiently attenuated to minimally interfere with a transmitter on any other channel. Due to the near-far problem a transmitter can impact a receiver on a "non-overlapping" channel, but only if it is close to the victim receiver or operating above allowed power levels. Conversely, a sufficiently distant transmitter on an overlapping channel can have little to no significant effect.
Confusion often arises over the amount of channel separation required between transmitting devices. 802.11b was based on direct-sequence spread spectrum modulation and utilized a channel bandwidth of 22 MHz, resulting in three "non-overlapping" channels. 802.11g was based on OFDM modulation and utilized a channel bandwidth of 20 MHz. This occasionally leads to the belief that four "non-overlapping" channels exist under 802.11g, although this is not the case as per 17.4.6.3 Channel Numbering of operating channels of the IEEE Std 802.11, which states "In a multiple cell network topology, overlapping and/or adjacent cells using different channels can operate simultaneously without interference if the distance between the center frequencies is at least 25 MHz."
and section 18.3.9.3 and Figure 18-13.
This does not mean that the technical overlap of the channels recommends the non-use of overlapping channels. The amount of inter-channel interference seen on a configuration using channels 1, 5, 9, and 13 is barely different from a three-channel configuration, but with an entire extra channel.
However, overlap between channels with more narrow spacing may cause unacceptable degradation of signal quality and throughput, particularly when users transmit near the boundaries of AP cells.

Regulatory domains and legal compliance

IEEE uses the phrase regdomain to refer to a legal regulatory region. Different countries define different levels of allowable transmitter power, time that a channel can be occupied, and different available channels. Domain codes are specified for the United States, Canada, ETSI, Spain, France, Japan, and China.
Most Wi-Fi certified devices default to regdomain 0, which means least common denominator settings, i.e., the device will not transmit at a power above the allowable power in any nation, nor will it use frequencies that are not permitted in any nation.
The regdomain setting is often made difficult or impossible to change so that the end users do not conflict with local regulatory agencies such as the United States' Federal Communications Commission.

Layer 2 – Datagrams

The datagrams are called frames. Current 802.11 standards specify frame types for use in transmission of data as well as management and control of wireless links.
Frames are divided into very specific and standardized sections. Each frame consists of a MAC header, payload, and frame check sequence. Some frames may not have a payload.
FieldFrame
control		Duration,
Address
1		Address
2		Address
3		Sequence
control		Address
4
control
control		Frame
body		Frame check
sequence
Length 226660, or 260, or 20, or 44

The first two bytes of the MAC header form a frame control field specifying the form and function of the frame. This frame control field is subdivided into the following sub-fields:
The next two bytes are reserved for the Duration ID field that indicates how long the field's transmission will take so other devices know when the channel will be available again. This field can take one of three forms: Duration, Contention-Free Period, and Association ID.
An 802.11 frame can have up to four address fields. Each field can carry a MAC address. Address 1 is the receiver, Address 2 is the transmitter, Address 3 is used for filtering purposes by the receiver. Address 4 is only present in data frames transmitted between access points in an Extended Service Set or between intermediate nodes in a mesh network.
The remaining fields of the header are:
The payload or frame body field is variable in size, from 0 to 2304 bytes plus any overhead from security encapsulation, and contains information from higher layers.
The Frame Check Sequence is the last four bytes in the standard 802.11 frame. Often referred to as the Cyclic Redundancy Check, it allows for integrity check of retrieved frames. As frames are about to be sent, the FCS is calculated and appended. When a station receives a frame, it can calculate the FCS of the frame and compare it to the one received. If they match, it is assumed that the frame was not distorted during transmission.

Management frames

Management frames are not always authenticated, and allow for the maintenance, or discontinuance, of communication. Some common 802.11 subtypes include:
The body of a management frame consists of frame-subtype-dependent fixed fields followed by a sequence of information elements.
The common structure of an IE is as follows:

Control frames

Control frames facilitate in the exchange of data frames between stations. Some common 802.11 control frames include:
Data frames carry packets from web pages, files, etc. within the body. The body begins with an IEEE 802.2 header, with the Destination Service Access Point specifying the protocol, followed by a Subnetwork Access Protocol header if the DSAP is hex AA, with the organizationally unique identifier and protocol ID fields specifying the protocol. If the OUI is all zeroes, the protocol ID field is an EtherType value. Almost all 802.11 data frames use 802.2 and SNAP headers, and most use an OUI of 00:00:00 and an EtherType value.
Similar to TCP congestion control on the internet, frame loss is built into the operation of 802.11. To select the correct transmission speed or Modulation and Coding Scheme, a rate control algorithm may test different speeds. The actual packet loss rate of an Access points vary widely for different link conditions. There are variations in the loss rate experienced on production Access points, between 10% and 80%, with 30% being a common average. It is important to be aware that the link layer should recover these lost frames. If the sender does not receive an Acknowledgement frame, then it will be resent.

Standards and amendments

Within the IEEE 802.11 Working Group, the following IEEE Standards Association Standard and Amendments exist:
802.11F and 802.11T are recommended practices rather than standards, and are capitalized as such.
802.11m is used for standard maintenance. 802.11ma was completed for 802.11-2007, 802.11mb for 802.11-2012, and 802.11mc for 802.11-2016.

Standard vs. amendment

Both the terms "standard" and "amendment" are used when referring to the different variants of IEEE standards.
As far as the IEEE Standards Association is concerned, there is only one current standard; it is denoted by IEEE 802.11 followed by the date that it was published. IEEE 802.11-2016 is the only version currently in publication, superseding previous releases. The standard is updated by means of amendments. Amendments are created by task groups. Both the task group and their finished document are denoted by 802.11 followed by a non-capitalized letter, for example, IEEE 802.11a and IEEE 802.11b. Updating 802.11 is the responsibility of task group m. In order to create a new version, TGm combines the previous version of the standard and all published amendments. TGm also provides clarification and interpretation to industry on published documents. New versions of the IEEE 802.11 were published in 1999, 2007, 2012, and 2016.

Nomenclature

Various terms in 802.11 are used to specify aspects of wireless local-area networking operation, and may be unfamiliar to some readers.
For example, Time Unit is used to indicate a unit of time equal to 1024 microseconds. Numerous time constants are defined in terms of TU.
Also the term "Portal" is used to describe an entity that is similar to an 802.1H bridge. A Portal provides access to the WLAN by non-802.11 LAN STAs.

Security

In 2001, a group from the University of California, Berkeley presented a paper describing weaknesses in the 802.11 Wired Equivalent Privacy security mechanism defined in the original standard; they were followed by Fluhrer, Mantin, and Shamir's paper titled "Weaknesses in the Key Scheduling Algorithm of RC4". Not long after, Adam Stubblefield and AT&T publicly announced the first verification of the attack. In the attack, they were able to intercept transmissions and gain unauthorized access to wireless networks.
The IEEE set up a dedicated task group to create a replacement security solution, 802.11i. The Wi-Fi Alliance announced an interim specification called Wi-Fi Protected Access based on a subset of the then current IEEE 802.11i draft. These started to appear in products in mid-2003. IEEE 802.11i itself was ratified in June 2004, and uses the Advanced Encryption Standard, instead of RC4, which was used in WEP. The modern recommended encryption for the home/consumer space is WPA2, and for the enterprise space is WPA2 along with a RADIUS authentication server and a strong authentication method such as EAP-TLS.
In January 2005, the IEEE set up yet another task group "w" to protect management and broadcast frames, which previously were sent unsecured. Its standard was published in 2009.
In December 2011, a security flaw was revealed that affects some wireless routers with a specific implementation of the optional Wi-Fi Protected Setup feature. While WPS is not a part of 802.11, the flaw allows an attacker within the range of the wireless router to recover the WPS PIN and, with it, the router's 802.11i password in a few hours.
In late 2014, Apple announced that its iOS 8 mobile operating system would scramble MAC addresses during the pre-association stage to thwart retail footfall tracking made possible by the regular transmission of uniquely identifiable probe requests.
Wi-Fi users may be subjected to a Wi-Fi deauthentication attack to eavesdrop, attack passwords or simply to force the use of another, usually more expensive access point.

Non-standard 802.11 extensions and equipment

Many companies implement wireless networking equipment with non-IEEE standard 802.11 extensions either by implementing proprietary or draft features. These changes may lead to incompatibilities between these extensions.

Footnotes