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Wikipedia

IEEE 802.11

IEEE 802.11 is part of the IEEE 802 set of local area network (LAN) technical standards, and specifies the set of media access control (MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN) computer communication. The standard and amendments provide the basis for wireless network products using the Wi-Fi brand and are the world's most widely used wireless computer networking standards. IEEE 802.11 is used in most home and office networks to allow laptops, printers, smartphones, and other devices to communicate with each other and access the Internet without connecting wires. IEEE 802.11 is also a basis for vehicle-based communication networks with IEEE 802.11p.

This Linksys WRT54GS Wi-Fi router operates on the 2.4 GHz "g" standard, capable of transmitting 54 Mbit/s.
For comparison, this Netgear dual-band router from 2013 uses the "ac" standard, capable of transmitting 1900 Mbit/s (combined).

The standards are created and maintained by the Institute of Electrical and Electronics Engineers (IEEE) LAN/MAN Standards Committee (IEEE 802). The base version of the standard was released in 1997 and has had subsequent amendments. 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 the capabilities of their products. As a result, in the marketplace, each revision tends to become its own standard.

IEEE 802.11 uses various frequencies including, but not limited to, 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz frequency bands. Although IEEE 802.11 specifications list channels that might be used, the radio frequency spectrum availability allowed varies significantly by regulatory domain.

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.

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 (CSMA/CA) whereby equipment listens to a channel for other users (including non 802.11 users) before transmitting each frame (some use the term "packet", which may be ambiguous: "frame" is more technically correct).

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 (c–f, h, j) are service amendments that are used to extend the current scope of the existing standard, which amendments may also include corrections to a previous specification.[1]

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 2.4-GHz 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. 802.11b and 802.11g control their interference and susceptibility to interference by using direct-sequence spread spectrum (DSSS) and orthogonal frequency-division multiplexing (OFDM) 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. This is an advantage over the 2.4-GHz, ISM-frequency band, which offers 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 (channels) may be realized, depending on the environment. 802.11n and 802.11ax 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.[2]

Generations

Wi-Fi generations
Generation IEEE
standard
Adopted Maximum
link rate
(Mbit/s)
Radio
frequency
(GHz)
Wi-Fi 7 802.11be (2024) 1376 to 46120 2.4/5/6
Wi-Fi 6E 802.11ax 2020 574 to 9608[3] 6[4]
Wi-Fi 6 2019 2.4/5
Wi-Fi 5 802.11ac 2014 433 to 6933 5[5]
Wi-Fi 4 802.11n 2008 72 to 600 2.4/5
(Wi-Fi 3)* 802.11g 2003 6 to 54 2.4
(Wi-Fi 2)* 802.11a 1999 6 to 54 5
(Wi-Fi 1)* 802.11b 1999 1 to 11 2.4
(Wi-Fi 0)* 802.11 1997 1 to 2 2.4
*(Wi-Fi 0, 1, 2, 3, are unbranded common usage)[6][7][8][9]

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.[10][11]

History

802.11 technology has its origins in a 1985 ruling by the U.S. Federal Communications Commission that released the ISM band[1] for unlicensed use.[12]

In 1991 NCR Corporation/AT&T (now Nokia Labs and LSI Corporation) 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.[13] He, along with Bell Labs Engineer Bruce Tuch, approached IEEE to create a standard.[14]

In 1999, the Wi-Fi Alliance was formed as a trade association to hold the Wi-Fi trademark under which most products are sold.[15]

The major commercial breakthrough came with Apple's 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.[16][17][18] One year later IBM followed with its ThinkPad 1300 series in 2000.[19]

Protocol

Frequency
range,
or type
PHY Protocol Release
date[20]
Frequency Bandwidth Stream
data rate[21]
Allowable
MIMO streams
Modulation Approximate
range
Indoor Outdoor
(GHz) (MHz) (Mbit/s)
1–6 GHz DSSS/FHSS[22] 802.11-1997 June 1997 2.4 22 1, 2 DSSS, FHSS 20 m (66 ft) 100 m (330 ft)
HR-DSSS[22] 802.11b September 1999 2.4 22 1, 2, 5.5, 11 DSSS 35 m (115 ft) 140 m (460 ft)
OFDM 802.11a September 1999 5 5/10/20 6, 9, 12, 18, 24, 36, 48, 54
(for 20 MHz bandwidth,
divide by 2 and 4 for 10 and 5 MHz)
OFDM 35 m (115 ft) 120 m (390 ft)
802.11j November 2004 4.9/5.0
[D][23]
? ?
802.11y November 2008 3.7[A] ? 5,000 m (16,000 ft)[A]
802.11p July 2010 5.9 250 m 1,000 m (3,300 ft)[24]
802.11bd December 2022
(est.)
5.9/60 500 m 1,000 m (3,300 ft)
ERP-OFDM 802.11g June 2003 2.4 38 m (125 ft) 140 m (460 ft)
HT-OFDM[25] 802.11n
(Wi-Fi 4)
October 2009 2.4/5 20 Up to 288.8[B] 4 MIMO-OFDM
(64-QAM)
70 m (230 ft) 250 m (820 ft)[26]
40 Up to 600[B]
VHT-OFDM[25] 802.11ac
(Wi-Fi 5)
December 2013 5 20 Up to 346.8[B] 8 DL
MU-MIMO OFDM
(256-QAM)
35 m (115 ft)[27] ?
40 Up to 800[B]
80 Up to 1733.2[B]
160 Up to 3466.8[B]
HE-OFDMA 802.11ax
(Wi-Fi 6,
Wi-Fi 6E)
May 2021 2.4/5/6 20 Up to 1147[F] 8 UL/DL
MU-MIMO OFDMA
(1024-QAM)
30 m (98 ft) 120 m (390 ft) [G]
40 Up to 2294[F]
80 Up to 4804[F]
80+80 Up to 9608[F]
EHT-OFDMA 802.11be
(Wi-Fi 7)
May 2024
(est.)
2.4/5/6 80 Up to 11.5 Gbit/s[F] 16 UL/DL
MU-MIMO OFDMA
(4096-QAM)
30 m (98 ft) 120 m (390 ft) [G]
160
(80+80)
Up to 23 Gbit/s[F]
240
(160+80)
Up to 35 Gbit/s[F]
320
(160+160)
Up to 46.1 Gbit/s[F]
WUR[E] 802.11ba October 2021 2.4/5 4/20 0.0625, 0.25
(62.5 kbit/s, 250 kbit/s)
OOK (Multi-carrier OOK) ? ?
mmWave DMG[28] 802.11ad December 2012 60 2160
(2.16 GHz)
Up to 6757[29]
(6.7 Gbit/s)
OFDM, single carrier, low-power single carrier 3.3 m (11 ft)[30] ?
802.11aj April 2018 45/60[C] 540/
1080[31]
Up to 15000[32]
(15 Gbit/s)
4[33] OFDM, single carrier[33] ? ?
EDMG[34] 802.11ay July 2021 60 8000
(8.0 GHz)
Up to 20000[35]
(20 Gbit/s)
4 OFDM, single carrier 10 m (33 ft) 100 m (328 ft)
Sub-gigaherz IoT TVHT[36] 802.11af February 2014 0.054
-0.79
6–8 Up to 568.9[37] 4 MIMO-OFDM ? ?
S1G[36] 802.11ah May 2017 0.7/0.8
/0.9
1–16 Up to 8.67[38]
(@2 MHz)
4 ? ?
Light (Li-Fi) LC
(VLC/OWC)
802.11bb December 2023
(est.)
800–1000 nm 20 Up to 9.6 Gbit/s O-OFDM ? ?
IR
(IrDA)
802.11-1997 June 1997 850–900 nm ? 1, 2 PPM ? ?
802.11 Standard rollups
  802.11-2007 March 2007 2.4, 5 Up to 54 DSSS, OFDM
802.11-2012 March 2012 2.4, 5 Up to 150[B] DSSS, OFDM
802.11-2016 December 2016 2.4, 5, 60 Up to 866.7 or 6757[B] DSSS, OFDM
802.11-2020 December 2020 2.4, 5, 60 Up to 866.7 or 6757[B] DSSS, OFDM
  • A1 A2 IEEE 802.11y-2008 extended operation of 802.11a to the licensed 3.7 GHz band. Increased power limits allow a range up to 5,000 m. As of 2009, it is only being licensed in the United States by the FCC.
  • B1 B2 B3 B4 B5 B6 Based on short guard interval; standard guard interval is ~10% slower. Rates vary widely based on distance, obstructions, and interference.
  • C1 For Chinese regulation.
  • D1 For Japanese regulation.
  • E1 Wake-up Radio (WUR) Operation.
  • F1 F2 F3 F4 For single-user cases only, based on default guard interval which is 0.8 micro seconds. Since multi-user via OFDMA has become available for 802.11ax, these may decrease. Also, these theoretical values depend on the link distance, whether the link is line-of-sight or not, interferences and the multi-path components in the environment.
  • G1 The default guard interval is 0.8 micro seconds. However, 802.11ax extended the maximum available guard interval to 3.2 micro seconds, in order to support Outdoor communications, where the maximum possible propagation delay is larger compared to Indoor environments.

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 (Mbit/s), 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 (physical layer) was added.

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.[39] 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 (802.11b will reduce speed to 5.5 Mbit/s or even 1 Mbit/s at low signal strengths). 802.11a also suffers from interference,[40] 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 (Megabits per second) 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 (compared to the original standard) 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 (users) 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 (like 802.11b), 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.[41] 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.[citation needed]

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.[citation needed] 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, the 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 (802.11a, b, d, e, g, h, i, j) with the base standard. Upon approval on 8 March 2007, 802.11REVma was renamed to the then-current base standard IEEE 802.11-2007.[42]

802.11n

802.11n is an amendment that improves upon the previous 802.11 standards; its first draft of certification was published in 2006. The 802.11n standard was retroactively labelled as Wi-Fi 4 by the Wi-Fi Alliance.[43][44] The standard added support for multiple-input multiple-output antennas (MIMO). 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.[45][46] 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.[47] REVmb or 802.11mb, as it was called, created a single document that merged ten amendments (802.11k, r, y, n, w, p, z, v, u, s) with the 2007 base standard. In addition much cleanup was done, including a reordering of many of the clauses.[48] 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.[49] The 802.11ac standard was retroactively labelled as Wi-Fi 5 by the Wi-Fi Alliance.[43][44] Changes compared to 802.11n include wider channels (80 or 160 MHz versus 40 MHz) in the 5 GHz band, more spatial streams (up to eight versus four), higher-order modulation (up to 256-QAM vs. 64-QAM), and the addition of Multi-user MIMO (MU-MIMO). The Wi-Fi Alliance separated the introduction of ac wireless products into two phases ("waves"), named "Wave 1" and "Wave 2".[50][51] From mid-2013, the alliance started certifying Wave 1 802.11ac products shipped by manufacturers, based on the IEEE 802.11ac Draft 3.0 (the IEEE standard was not finalized until later that year).[52] 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 (with four antennas; compared to three in Wave 1 and 802.11n, and eight in IEEE's 802.11ax specification).[53][54]

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.[55] The peak transmission rate of 802.11ad is 7 Gbit/s.[56]

IEEE 802.11ad is a protocol used for very high data rates (about 8 Gbit/s) and for short range communication (about 1–10 meters).[57]

TP-Link announced the world's first 802.11ad router in January 2016.[58]

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",[59] 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.[60][61] 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.[61] Access points and stations determine their position using a satellite positioning system such as GPS, and use the Internet to query a geolocation database (GDB) provided by a regional regulatory agency to discover what frequency channels are available for use at a given time and position.[61] The physical layer uses OFDM and is based on 802.11ac.[62] 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.[61] The frequency channels are 6 to 8 MHz wide, depending on the regulatory domain.[61] Up to four channels may be bonded in either one or two contiguous blocks.[61] MIMO operation is possible with up to four streams used for either space–time block code (STBC) or multi-user (MU) operation.[61] 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.[37] 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.[37]

802.11-2016

IEEE 802.11-2016 which was known as IEEE 802.11 REVmc,[63] is a revision based on IEEE 802.11-2012, incorporating 5 amendments (11ae, 11aa, 11ad, 11ac, 11af). 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.[64]

802.11ah

IEEE 802.11ah, published in 2017,[65] 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,[66] 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.[67]

802.11ai

IEEE 802.11ai is an amendment to the 802.11 standard that added new mechanisms for a faster initial link setup time.[68]

802.11aj

IEEE 802.11aj is a derivative of 802.11ad for use in the 45 GHz unlicensed spectrum available in some regions of the world (specifically China); it also provides additional capabilities for use in the 60 GHz band.[68]

Alternatively known as China Millimeter Wave (CMMW).

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 discover further the services running on a device, or provided by a network.[68]

802.11-2020

IEEE 802.11-2020, which was known as IEEE 802.11 REVmd,[69] is a revision based on IEEE 802.11-2016 incorporating 5 amendments (11ai, 11ah, 11aj, 11ak, 11aq). 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 added.[70]

802.11ax

IEEE 802.11ax is the successor to 802.11ac, marketed as Wi-Fi 6 (2.4 GHz and 5 GHz)[71] and Wi-Fi 6E (6 GHz)[72] by the Wi-Fi Alliance. It is also known as High Efficiency Wi-Fi, for the overall improvements to Wi-Fi 6 clients under dense environments.[73] For an individual client, the maximum improvement in data rate (PHY speed) against the predecessor (802.11ac) is only 39%[a] (for comparison, this improvement was nearly 500%[b][i] for the predecessors).[c] Yet, even with this comparatively minor 39% figure, the goal was to provide 4 times the throughput-per-area[d] of 802.11ac (hence High Efficiency). The motivation behind this goal was the deployment of WLAN in dense environments such as corporate offices, shopping malls and dense residential apartments.[73] This is achieved by means of a technique called OFDMA, which is basically multiplexing in the frequency domain (as opposed to spatial multiplexing, as in 802.11ac). This is equivalent to cellular technology applied into Wi-Fi.[73]: qt

The IEEE 802.11ax‑2021 standard was approved on February 9, 2021.[76][77]

802.11ay

IEEE 802.11ay is a standard that is being developed, also called EDMG: Enhanced Directional MultiGigabit PHY. 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 and short-range communications due to atmospheric oxygen absorption and inability to penetrate walls. The peak transmission rate of 802.11ay is 40 Gbit/s.[78] The main extensions include: channel bonding (2, 3 and 4), MIMO (up to 4 streams) and higher modulation schemes. The expected range is 300-500 m.[79]

802.11ba

IEEE 802.11ba Wake-up Radio (WUR) Operation is an amendment to the IEEE 802.11 standard that enables energy efficient operation for data reception without increasing latency.[80] The target active power consumption to receive a WUR packet is less than 1 milliwatt and supports data rates of 62.5 kbit/s and 250 kbit/s. The WUR PHY uses MC-OOK (multicarrier OOK) to achieve extremely low power consumption.[81]

802.11be

IEEE 802.11be Extremely High Throughput (EHT) is the potential next amendment to the 802.11 IEEE standard,[82] and will likely be designated as Wi-Fi 7.[83][84] 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

 
Graphical representation of Wi-Fi application specific (UDP) performance envelope 2.4 GHz band, with 802.11g. 1 Mbps = 1 Mbit/s

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.

 
Graphical representation of Wi-Fi application specific (UDP) performance envelope 2.4 GHz band, with 802.11n with 40MHz

This means that, typically, data frames pass an 802.11 (WLAN) medium and are being converted to 802.3 (Ethernet) or vice versa. Due to the difference in the frame (header) lengths of these two media, the application's packet size determines the speed of the data transfer. This means applications that use small packets (e.g., VoIP) create dataflows with high-overhead traffic (i.e., a low goodput). Other factors that contribute to the overall application data rate are the speed with which the application transmits the packets (i.e., the data rate) 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.[85][86]

The same references apply to the attached graphs that show measurements of UDP throughput. Each represents an average (UDP) throughput (please note that the error bars are there but barely visible due to the small variation) of 25 measurements. Each is with a specific packet size (small or large) and with a specific data rate (10 kbit/s – 100 Mbit/s). Markers for traffic profiles of common applications are included as well. These figures assume there are no packet errors, which, if occurring, will lower the transmission rate further.

Channels and frequencies

802.11b, 802.11g, and 802.11n-2.4 utilize the 2.400–2.500 GHz spectrum, one of the ISM bands. 802.11a, 802.11n, and 802.11ac use the more heavily regulated 4.915–5.825 GHz 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 how 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.

 
Graphical representation of Wi-Fi channels in the 2.4 GHz band

The channel numbering of the 5.725–5.875 GHz 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 (in Clause 17) a spectral mask defining the permitted power distribution across each channel. The mask requires the signal to be attenuated a minimum of 20 dB from its peak amplitude at ±11 MHz from the center 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 1–13 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.[87][88] North America and some Central and South American countries allow only 1 through 11.

 
Spectral masks for 802.11g channels 1–14 in the 2.4 GHz band

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 the overlapping signal on any channel should be sufficiently attenuated to interfere with a transmitter on any other channel minimally, given the separation between channels. Due to the near–far problem a transmitter can impact (desensitize) a receiver on a "non-overlapping" channel, but only if it is close to the victim receiver (within a meter) 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 (DSSS) modulation and utilized a channel bandwidth of 22 MHz, resulting in three "non-overlapping" channels (1, 6, and 11). 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 (1, 5, 9, and 13) exist under 802.11g. However, this is not the case as per 17.4.6.3 Channel Numbering of operating channels of the IEEE Std 802.11 (2012), 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."[89] 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 (which is permitted in Europe, but not in North America) is barely different from a three-channel configuration, but with an entire extra channel.[90][91]

 
802.11 non-overlapping channels for 2.4GHz. Covers 802.11b,g,n

However, overlap between channels with more narrow spacing (e.g. 1, 4, 7, 11 in North America) may cause unacceptable degradation of signal quality and throughput, particularly when users transmit near the boundaries of AP cells.[92]

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.[93] Domain codes are specified for the United States, Canada, ETSI (Europe), 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.[citation needed]

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.[citation needed]

Layer 2 – Datagrams

The datagrams are called frames. Current 802.11 standards specify frame types for use in the 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 (FCS). Some frames may not have a payload.

Field Frame
control
Duration,
id.
Address
1
Address
2
Address
3
Sequence
control
Address
4
QoS
control
HT
control
Frame
body
Frame check
sequence
Length (Bytes) 2 2 6 6 6 0, or 2 6 0, or 2 0, or 4 Variable 4

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:

  • Protocol Version: Two bits representing the protocol version. The currently used protocol version is zero. Other values are reserved for future use.
  • Type: Two bits identifying the type of WLAN frame. Control, Data, and Management are various frame types defined in IEEE 802.11.
  • Subtype: Four bits providing additional discrimination between frames. Type and Subtype are used together to identify the exact frame.
  • ToDS and FromDS: Each is one bit in size. They indicate whether a data frame is headed for a distribution system or it is getting out of it. Control and management frames set these values to zero. All the data frames will have one of these bits set.
    • ToDS = 0 and FromDS = 0
    • ToDS = 0 and FromDS = 1
      • A frame sent by a station and directed to an AP accessed via the distribution system.
    • ToDS = 1 and FromDS = 0
      • A frame exiting the distribution system for a station.
    • ToDS = 1 and FromDS = 1
      • Only kind of frame frame that uses all four MAC addresses in a DATA frame.
      • Address 1: final station address.
      • Address 2: access point address exiting from the distribution system.
      • Address 3: access point entrance to the distribution system (AP to which the source station is connected).
      • Address 4: address of the source station.[94]
  • More Fragments: The More Fragments bit is set when a packet is divided into multiple frames for transmission. Every frame except the last frame of a packet will have this bit set.
  • Retry: Sometimes frames require retransmission, and for this, there is a Retry bit that is set to one when a frame is resent. This aids in the elimination of duplicate frames.
  • Power Management: This bit indicates the power management state of the sender after the completion of a frame exchange. Access points are required to manage the connection and will never set the power-saver bit.
  • More Data: The More Data bit is used to buffer frames received in a distributed system. The access point uses this bit to facilitate stations in power-saver mode. It indicates that at least one frame is available and addresses all stations connected.
  • Protected Frame: The Protected Frame bit is set to the value of one if the frame body is encrypted by a protection mechanism such as Wired Equivalent Privacy (WEP), Wi-Fi Protected Access (WPA), or Wi-Fi Protected Access II (WPA2).
  • Order: This bit is set only when the "strict ordering" delivery method is employed. Frames and fragments are not always sent in order as it causes a transmission performance penalty.

The next two bytes are reserved for the Duration ID field, indicating 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 (CFP), and Association ID (AID).

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.[dubious ] 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 Sequence Control field is a two-byte section used to identify message order and eliminate duplicate frames. The first 4 bits are used for the fragmentation number, and the last 12 bits are the sequence number.
  • An optional two-byte Quality of Service control field, present in QoS Data frames; it was added with 802.11e.

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 (FCS) is the last four bytes in the standard 802.11 frame. Often referred to as the Cyclic Redundancy Check (CRC), it allows for integrity checks 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.[95]

Management frames

Management frames are not always authenticated, and allow for the maintenance, or discontinuance, of communication. Some common 802.11 subtypes include:

  • Authentication frame: 802.11 authentication begins with the wireless network interface card (WNIC) sending an authentication frame to the access point containing its identity.
    • When open system authentication is being used, the WNIC sends only a single authentication frame, and the access point responds with an authentication frame of its own indicating acceptance or rejection.
    • When shared key authentication is being used, the WNIC sends an initial authentication request, and the access point responds with an authentication frame containing challenge text. The WNIC then sends an authentication frame containing the encrypted version of the challenge text to the access point. The access point ensures the text was encrypted with the correct key by decrypting it with its own key. The result of this process determines the WNIC's authentication status.
  • Association request frame: Sent from a station, it enables the access point to allocate resources and synchronize. The frame carries information about the WNIC, including supported data rates and the SSID of the network the station wishes to associate with. If the request is accepted, the access point reserves memory and establishes an association ID for the WNIC.
  • Association response frame: Sent from an access point to a station containing the acceptance or rejection to an association request. If it is an acceptance, the frame will contain information such as an association ID and supported data rates.
  • Beacon frame: Sent periodically from an access point to announce its presence and provide the SSID, and other parameters for WNICs within range.
  • Deauthentication frame: Sent from a station wishing to terminate connection from another station.
  • Disassociation frame: Sent from a station wishing to terminate the connection. It is an elegant way to allow the access point to relinquish memory allocation and remove the WNIC from the association table.
  • Probe request frame: Sent from a station when it requires information from another station.
  • Probe response frame: Sent from an access point containing capability information, supported data rates, etc., after receiving a probe request frame.
  • Reassociation request frame: A WNIC sends a reassociation request when it drops from the currently associated access point range and finds another access point with a stronger signal. The new access point coordinates the forwarding of any information that may still be contained in the buffer of the previous access point.
  • Reassociation response frame: Sent from an access point containing the acceptance or rejection to a WNIC reassociation request frame. The frame includes information required for association such as the association ID and supported data rates.
  • Action frame: extending management frame to control a certain action. Some of the action categories are Block Ack, Radio Measurement, Fast BSS Transition, etc. These frames are sent by a station when it needs to tell its peer for a certain action to be taken. For example, a station can tell another station to set up a block acknowledgement by sending an ADDBA Request action frame. The other station would then respond with an ADDBA Response action frame.

The body of a management frame consists of frame-subtype-dependent fixed fields followed by a sequence of information elements (IEs).

The common structure of an IE is as follows:

Field Type Length Data
Length 1 1 1–252

Control frames

Control frames facilitate the exchange of data frames between stations. Some common 802.11 control frames include:

  • Acknowledgement (ACK) frame: After receiving a data frame, the receiving station will send an ACK frame to the sending station if no errors are found. If the sending station doesn't receive an ACK frame within a predetermined period of time, the sending station will resend the frame.
  • Request to Send (RTS) frame: The RTS and CTS frames provide an optional collision reduction scheme for access points with hidden stations. A station sends an RTS frame as the first step in a two-way handshake required before sending data frames.
  • Clear to Send (CTS) frame: A station responds to an RTS frame with a CTS frame. It provides clearance for the requesting station to send a data frame. The CTS provides collision control management by including a time value for which all other stations are to hold off transmission while the requesting station transmits.

Data frames

Data frames carry packets from web pages, files, etc. within the body.[96] The body begins with an IEEE 802.2 header, with the Destination Service Access Point (DSAP) specifying the protocol, followed by a Subnetwork Access Protocol (SNAP) header if the DSAP is hex AA, with the organizationally unique identifier (OUI) and protocol ID (PID) fields specifying the protocol. If the OUI is all zeroes, the protocol ID field is an EtherType value.[97] 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 Access points varies 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.[98] It is important to be aware that the link layer should recover these lost frames. If the sender does not receive an Acknowledgement (ACK) frame, then it will be resent.

Standards and amendments

Within the IEEE 802.11 Working Group,[60] the following IEEE Standards Association Standard and Amendments exist:

  • IEEE 802.11-1997: The WLAN standard was originally 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF and infrared (IR) standard (1997), all the others listed below are Amendments to this standard, except for Recommended Practices 802.11F and 802.11T.
  • IEEE 802.11a: 54 Mbit/s, 5 GHz standard (1999, shipping products in 2001)
  • IEEE 802.11b: 5.5 Mbit/s and 11 Mbit/s, 2.4 GHz standard (1999)
  • IEEE 802.11c: Bridge operation procedures; included in the IEEE 802.1D standard (2001)
  • IEEE 802.11d: International (country-to-country) roaming extensions (2001)
  • IEEE 802.11e: Enhancements: QoS, including packet bursting (2005)
  • IEEE 802.11F: Inter-Access Point Protocol (2003) Withdrawn February 2006
  • IEEE 802.11g: 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003)
  • IEEE 802.11h: Spectrum Managed 802.11a (5 GHz) for European compatibility (2004)
  • IEEE 802.11i: Enhanced security (2004)
  • IEEE 802.11j: Extensions for Japan (4.9-5.0 GHz) (2004)
  • IEEE 802.11-2007: A new release of the standard that includes amendments a, b, d, e, g, h, i, and j. (July 2007)
  • IEEE 802.11k: Radio resource measurement enhancements (2008)
  • IEEE 802.11n: Higher Throughput WLAN at 2.4 and 5 GHz; 20 and 40 MHz channels; introduces MIMO to Wi-Fi (September 2009)
  • IEEE 802.11p: WAVE—Wireless Access for the Vehicular Environment (such as ambulances and passenger cars) (July 2010)
  • IEEE 802.11r: Fast BSS transition (FT) (2008)
  • IEEE 802.11s: Mesh Networking, Extended Service Set (ESS) (July 2011)
  • IEEE 802.11T: Wireless Performance Prediction (WPP)—test methods and metrics Recommendation cancelled
  • IEEE 802.11u: Improvements related to HotSpots and 3rd-party authorization of clients, e.g., cellular network offload (February 2011)
  • IEEE 802.11v: Wireless network management (February 2011)
  • IEEE 802.11w: Protected Management Frames (September 2009)
  • IEEE 802.11y: 3650–3700 MHz Operation in the U.S. (2008)
  • IEEE 802.11z: Extensions to Direct Link Setup (DLS) (September 2010)
  • IEEE 802.11-2012: A new release of the standard that includes amendments k, n, p, r, s, u, v, w, y, and z (March 2012)
  • IEEE 802.11aa: Robust streaming of Audio Video Transport Streams (June 2012) - see Stream Reservation Protocol
  • IEEE 802.11ac: Very High Throughput WLAN at 5 GHz[e]; wider channels (80 and 160 MHz); Multi-user MIMO (down-link only)[99] (December 2013)
  • IEEE 802.11ad: Very High Throughput 60 GHz (December 2012) — see also WiGig
  • IEEE 802.11ae: Prioritization of Management Frames (March 2012)
  • IEEE 802.11af: TV Whitespace (February 2014)
  • IEEE 802.11-2016: A new release of the standard that includes amendments aa, ac, ad, ae, and af (December 2016)
  • IEEE 802.11ah: Sub-1 GHz license exempt operation (e.g., sensor network, smart metering) (December 2016)
  • IEEE 802.11ai: Fast Initial Link Setup (December 2016)
  • IEEE 802.11aj: China Millimeter Wave (February 2018)
  • IEEE 802.11ak: Transit Links within Bridged Networks (June 2018)
  • IEEE 802.11aq: Pre-association Discovery (July 2018)
  • IEEE 802.11-2020: A new release of the standard that includes amendments ah, ai, aj, ak, and aq (December 2020)
  • IEEE 802.11ax: High Efficiency WLAN at 2.4, 5 and 6 GHz;[f] introduces OFDMA to Wi-Fi[73] (February 2021)
  • IEEE 802.11ay: Enhancements for Ultra High Throughput in and around the 60 GHz Band (March 2021)
  • IEEE 802.11az: Next Generation Positioning (March 2023)
  • IEEE 802.11ba: Wake Up Radio (March 2021)
  • IEEE 802.11bd: Enhancements for Next Generation V2X (see also IEEE 802.11p) (March 2023)

In process

  • IEEE 802.11bb: Light Communications (Dec 2023)
  • IEEE 802.11bc: Enhanced Broadcast Service (Dec 2023)
  • IEEE 802.11be: Extremely High Throughput (see also IEEE 802.11ax) (May 2024)
  • IEEE 802.11bf: WLAN Sensing
  • IEEE 802.11bh: Randomized and Changing MAC Addresses
  • IEEE 802.11bi: Enhanced Data Privacy
  • IEEE 802.11bk: 320 MHz Positioning
  • IEEE 802.11me: 802.11 Accumulated Maintenance Changes

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, 802.11mc for 802.11-2016, and 802.11md for 802.11-2020.

Standard vs. amendment

Both the terms "standard" and "amendment" are used when referring to the different variants of IEEE standards.[100]

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 published. IEEE 802.11-2020 is the only version currently in publication, superseding previous releases. The standard is updated by means of amendments. Amendments are created by task groups (TG). Both the task group and their finished document are denoted by 802.11 followed by one or two lower case letters, for example, IEEE 802.11a or IEEE 802.11ax. 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, 2016, and 2020.[101][102]

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 (usually abbreviated TU) is used to indicate a unit of time equal to 1024 microseconds. Numerous time constants are defined in terms of TU (rather than the nearly equal millisecond).

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 (WEP) 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.[103]

The IEEE set up a dedicated task group to create a replacement security solution, 802.11i (previously, this work was handled as part of a broader 802.11e effort to enhance the MAC layer). The Wi-Fi Alliance announced an interim specification called Wi-Fi Protected Access (WPA) based on a subset of the then-current IEEE 802.11i draft. These started to appear in products in mid-2003. IEEE 802.11i (also known as WPA2) itself was ratified in June 2004, and uses the Advanced Encryption Standard (AES), instead of RC4, which was used in WEP. The modern recommended encryption for the home/consumer space is WPA2 (AES Pre-Shared Key), and for the enterprise space is WPA2 along with a RADIUS authentication server (or another type of authentication server) and a strong authentication method such as EAP-TLS.[citation needed]

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.[104]

In December 2011, a security flaw was revealed that affects some wireless routers with a specific implementation of the optional Wi-Fi Protected Setup (WPS) 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.[105][106]

In late 2014, Apple announced that its iOS 8 mobile operating system would scramble MAC addresses[107] during the pre-association stage to thwart retail footfall tracking made possible by the regular transmission of uniquely identifiable probe requests.[citation needed]

Wi-Fi users may be subjected to a Wi-Fi deauthentication attack to eavesdrop, attack passwords, or force the use of another, usually more expensive access point.[108]

See also

Notes

  1. ^ 802.11ax with 2402 Mbit/s (MCS Index 11, 2 spatial streams, 160 MHz); versus 802.11ac with 1733.3 Mbit/s (MCS Index 9, 2 spatial streams, 160 MHz).[74]
  2. ^ 802.11ac with 1733.3 Mbit/s (MCS Index 9, 2 spatial streams, 160 MHz); versus 802.11n with 300 Mbit/s (MCS Index 7, 2 spatial streams, 40 MHz
  3. ^ An IEEE article considers only a 37% growth for 802.11ax and a 1000% growth for both 802.11ac and 802.11n.[73]
  4. ^ Throughput-per-area, as defined by IEEE, is the ratio of the total network throughput to the network area.[73]
  5. ^ Operation in the 2.4 GHz band is specified by 802.11n.
  6. ^ 6 GHz operation only between Wi-Fi 6E devices.
  1. ^ This improvement is 1100% if we consider 144.4 Mbit/s (MCS Index 15, 2 spatial streams, 20 MHz), due to 40 MHz mode from 802.11n (at 2.4 GHz) having little practical use in most scenarios.[75]: qt).[74]

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References

  • IEEE 802.11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. (2016 revision). IEEE-SA. 14 December 2016. doi:10.1109/IEEESTD.2016.7786995. ISBN 978-1-5044-3645-8.
  • IEEE 802.11k-2008—Amendment 1: Radio Resource Measurement of Wireless LANs (PDF). IEEE-SA. 12 June 2008. doi:10.1109/IEEESTD.2008.4544755. ISBN 978-0-7381-5420-6.
  • IEEE 802.11r-2008—Amendment 2: Fast Basic Service Set (BSS) Transition (PDF). IEEE-SA. 15 July 2008. doi:10.1109/IEEESTD.2008.4573292. ISBN 978-0-7381-5422-0.
  • IEEE 802.11y-2008—Amendment 3: 3650–3700 MHz Operation in USA (PDF). IEEE-SA. 6 November 2008. doi:10.1109/IEEESTD.2008.4669928. ISBN 978-0-7381-5765-8.

External links

  • IEEE 802.11 working group
  • Official timelines of 802.11 standards from IEEE
  • – Including historical timeline of mergers and acquisitions

ieee, part, ieee, local, area, network, technical, standards, specifies, media, access, control, physical, layer, protocols, implementing, wireless, local, area, network, wlan, computer, communication, standard, amendments, provide, basis, wireless, network, p. IEEE 802 11 is part of the IEEE 802 set of local area network LAN technical standards and specifies the set of media access control MAC and physical layer PHY protocols for implementing wireless local area network WLAN computer communication The standard and amendments provide the basis for wireless network products using the Wi Fi brand and are the world s most widely used wireless computer networking standards IEEE 802 11 is used in most home and office networks to allow laptops printers smartphones and other devices to communicate with each other and access the Internet without connecting wires IEEE 802 11 is also a basis for vehicle based communication networks with IEEE 802 11p This Linksys WRT54GS Wi Fi router operates on the 2 4 GHz g standard capable of transmitting 54 Mbit s For comparison this Netgear dual band router from 2013 uses the ac standard capable of transmitting 1900 Mbit s combined The standards are created and maintained by the Institute of Electrical and Electronics Engineers IEEE LAN MAN Standards Committee IEEE 802 The base version of the standard was released in 1997 and has had subsequent amendments 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 the capabilities of their products As a result in the marketplace each revision tends to become its own standard IEEE 802 11 uses various frequencies including but not limited to 2 4 GHz 5 GHz 6 GHz and 60 GHz frequency bands Although IEEE 802 11 specifications list channels that might be used the radio frequency spectrum availability allowed varies significantly by regulatory domain 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 Contents 1 General description 2 Generations 3 History 4 Protocol 4 1 802 11 1997 802 11 legacy 4 2 802 11a OFDM waveform 4 3 802 11b 4 4 802 11g 4 5 802 11 2007 4 6 802 11n 4 7 802 11 2012 4 8 802 11ac 4 9 802 11ad 4 10 802 11af 4 11 802 11 2016 4 12 802 11ah 4 13 802 11ai 4 14 802 11aj 4 15 802 11aq 4 16 802 11 2020 4 17 802 11ax 4 18 802 11ay 4 19 802 11ba 4 20 802 11be 5 Common misunderstandings about achievable throughput 6 Channels and frequencies 6 1 Channel spacing within the 2 4 GHz band 6 2 Regulatory domains and legal compliance 7 Layer 2 Datagrams 7 1 Management frames 7 2 Control frames 7 3 Data frames 8 Standards and amendments 8 1 In process 8 2 Standard vs amendment 9 Nomenclature 10 Security 11 See also 12 Notes 13 Footnotes 14 References 15 External linksGeneral description EditThe 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 CSMA CA whereby equipment listens to a channel for other users including non 802 11 users before transmitting each frame some use the term packet which may be ambiguous frame is more technically correct 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 c f h j are service amendments that are used to extend the current scope of the existing standard which amendments may also include corrections to a previous specification 1 802 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 2 4 GHz 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 802 11b and 802 11g control their interference and susceptibility to interference by using direct sequence spread spectrum DSSS and orthogonal frequency division multiplexing OFDM 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 This is an advantage over the 2 4 GHz ISM frequency band which offers 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 channels may be realized depending on the environment 802 11n and 802 11ax 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 2 Generations EditWi Fi generations Generation IEEEstandard Adopted Maximumlink rate Mbit s Radiofrequency GHz Wi Fi 7 802 11be 2024 1376 to 46120 2 4 5 6Wi Fi 6E 802 11ax 2020 574 to 9608 3 6 4 Wi Fi 6 2019 2 4 5Wi Fi 5 802 11ac 2014 433 to 6933 5 5 Wi Fi 4 802 11n 2008 72 to 600 2 4 5 Wi Fi 3 802 11g 2003 6 to 54 2 4 Wi Fi 2 802 11a 1999 6 to 54 5 Wi Fi 1 802 11b 1999 1 to 11 2 4 Wi Fi 0 802 11 1997 1 to 2 2 4 Wi Fi 0 1 2 3 are unbranded common usage 6 7 8 9 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 10 11 History Edit802 11 technology has its origins in a 1985 ruling by the U S Federal Communications Commission that released the ISM band 1 for unlicensed use 12 In 1991 NCR Corporation AT amp T now Nokia Labs and LSI Corporation 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 13 He along with Bell Labs Engineer Bruce Tuch approached IEEE to create a standard 14 In 1999 the Wi Fi Alliance was formed as a trade association to hold the Wi Fi trademark under which most products are sold 15 The major commercial breakthrough came with Apple s 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 16 17 18 One year later IBM followed with its ThinkPad 1300 series in 2000 19 Protocol Editvte802 11 network standardsFrequencyrange or type PHY Protocol Releasedate 20 Frequency Bandwidth Streamdata rate 21 AllowableMIMO streams Modulation ApproximaterangeIndoor Outdoor GHz MHz Mbit s 1 6 GHz DSSS FHSS 22 802 11 1997 June 1997 2 4 22 1 2 DSSS FHSS 20 m 66 ft 100 m 330 ft HR DSSS 22 802 11b September 1999 2 4 22 1 2 5 5 11 DSSS 35 m 115 ft 140 m 460 ft OFDM 802 11a September 1999 5 5 10 20 6 9 12 18 24 36 48 54 for 20 MHz bandwidth divide by 2 and 4 for 10 and 5 MHz OFDM 35 m 115 ft 120 m 390 ft 802 11j November 2004 4 9 5 0 D 23 802 11y November 2008 3 7 A 5 000 m 16 000 ft A 802 11p July 2010 5 9 250 m 1 000 m 3 300 ft 24 802 11bd December 2022 est 5 9 60 500 m 1 000 m 3 300 ft ERP OFDM 802 11g June 2003 2 4 38 m 125 ft 140 m 460 ft HT OFDM 25 802 11n Wi Fi 4 October 2009 2 4 5 20 Up to 288 8 B 4 MIMO OFDM 64 QAM 70 m 230 ft 250 m 820 ft 26 40 Up to 600 B VHT OFDM 25 802 11ac Wi Fi 5 December 2013 5 20 Up to 346 8 B 8 DLMU MIMO OFDM 256 QAM 35 m 115 ft 27 40 Up to 800 B 80 Up to 1733 2 B 160 Up to 3466 8 B HE OFDMA 802 11ax Wi Fi 6 Wi Fi 6E May 2021 2 4 5 6 20 Up to 1147 F 8 UL DLMU MIMO OFDMA 1024 QAM 30 m 98 ft 120 m 390 ft G 40 Up to 2294 F 80 Up to 4804 F 80 80 Up to 9608 F EHT OFDMA 802 11be Wi Fi 7 May 2024 est 2 4 5 6 80 Up to 11 5 Gbit s F 16 UL DLMU MIMO OFDMA 4096 QAM 30 m 98 ft 120 m 390 ft G 160 80 80 Up to 23 Gbit s F 240 160 80 Up to 35 Gbit s F 320 160 160 Up to 46 1 Gbit s F WUR E 802 11ba October 2021 2 4 5 4 20 0 0625 0 25 62 5 kbit s 250 kbit s OOK Multi carrier OOK mmWave DMG 28 802 11ad December 2012 60 2160 2 16 GHz Up to 6757 29 6 7 Gbit s OFDM single carrier low power single carrier 3 3 m 11 ft 30 802 11aj April 2018 45 60 C 540 1080 31 Up to 15000 32 15 Gbit s 4 33 OFDM single carrier 33 EDMG 34 802 11ay July 2021 60 8000 8 0 GHz Up to 20000 35 20 Gbit s 4 OFDM single carrier 10 m 33 ft 100 m 328 ft Sub gigaherz IoT TVHT 36 802 11af February 2014 0 054 0 79 6 8 Up to 568 9 37 4 MIMO OFDM S1G 36 802 11ah May 2017 0 7 0 8 0 9 1 16 Up to 8 67 38 2 MHz 4 Light Li Fi LC VLC OWC 802 11bb December 2023 est 800 1000 nm 20 Up to 9 6 Gbit s O OFDM IR IrDA 802 11 1997 June 1997 850 900 nm 1 2 PPM 802 11 Standard rollups 802 11 2007 March 2007 2 4 5 Up to 54 DSSS OFDM802 11 2012 March 2012 2 4 5 Up to 150 B DSSS OFDM802 11 2016 December 2016 2 4 5 60 Up to 866 7 or 6757 B DSSS OFDM802 11 2020 December 2020 2 4 5 60 Up to 866 7 or 6757 B DSSS OFDMA1 A2 IEEE 802 11y 2008 extended operation of 802 11a to the licensed 3 7 GHz band Increased power limits allow a range up to 5 000 m As of 2009 update it is only being licensed in the United States by the FCC B1 B2 B3 B4 B5 B6 Based on short guard interval standard guard interval is 10 slower Rates vary widely based on distance obstructions and interference C1 For Chinese regulation D1 For Japanese regulation E1 Wake up Radio WUR Operation F1 F2 F3 F4 For single user cases only based on default guard interval which is 0 8 micro seconds Since multi user via OFDMA has become available for 802 11ax these may decrease Also these theoretical values depend on the link distance whether the link is line of sight or not interferences and the multi path components in the environment G1 The default guard interval is 0 8 micro seconds However 802 11ax extended the maximum available guard interval to 3 2 micro seconds in order to support Outdoor communications where the maximum possible propagation delay is larger compared to Indoor environments 802 11 1997 802 11 legacy Edit Main article IEEE 802 11 legacy mode 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 Mbit s 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 Edit Main article IEEE 802 11a 1999 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 physical layer was added 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 39 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 11b will reduce speed to 5 5 Mbit s or even 1 Mbit s at low signal strengths 802 11a also suffers from interference 40 but locally there may be fewer signals to interfere with resulting in less interference and better throughput 802 11b Edit Main article IEEE 802 11b 1999 The 802 11b standard has a maximum raw data rate of 11 Mbit s Megabits per second 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 compared to the original standard 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 users of this band such as amateur radio 802 11g Edit Main article IEEE 802 11g 2003 In June 2003 a third modulation standard was ratified 802 11g This works in the 2 4 GHz band like 802 11b 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 41 802 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 citation needed 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 citation needed 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 the 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 Edit 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 802 11a b d e g h i j with the base standard Upon approval on 8 March 2007 802 11REVma was renamed to the then current base standard IEEE 802 11 2007 42 802 11n Edit Main article IEEE 802 11n 2009 802 11n is an amendment that improves upon the previous 802 11 standards its first draft of certification was published in 2006 The 802 11n standard was retroactively labelled as Wi Fi 4 by the Wi Fi Alliance 43 44 The standard added support for multiple input multiple output antennas MIMO 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 45 46 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 Edit In May 2007 task group TGmb was authorized to roll up many of the amendments to the 2007 version of the 802 11 standard 47 REVmb or 802 11mb as it was called created a single document that merged ten amendments 802 11k r y n w p z v u s with the 2007 base standard In addition much cleanup was done including a reordering of many of the clauses 48 Upon publication on 29 March 2012 the new standard was referred to as IEEE 802 11 2012 802 11ac Edit Main article IEEE 802 11ac IEEE 802 11ac 2013 is an amendment to IEEE 802 11 published in December 2013 that builds on 802 11n 49 The 802 11ac standard was retroactively labelled as Wi Fi 5 by the Wi Fi Alliance 43 44 Changes compared to 802 11n include wider channels 80 or 160 MHz versus 40 MHz in the 5 GHz band more spatial streams up to eight versus four higher order modulation up to 256 QAM vs 64 QAM and the addition of Multi user MIMO MU MIMO The Wi Fi Alliance separated the introduction of ac wireless products into two phases waves named Wave 1 and Wave 2 50 51 From mid 2013 the alliance started certifying Wave 1 802 11ac products shipped by manufacturers based on the IEEE 802 11ac Draft 3 0 the IEEE standard was not finalized until later that year 52 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 with four antennas compared to three in Wave 1 and 802 11n and eight in IEEE s 802 11ax specification 53 54 802 11ad Edit This section needs to be updated Please help update this article to reflect recent events or newly available information November 2013 Main article IEEE 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 55 The peak transmission rate of 802 11ad is 7 Gbit s 56 IEEE 802 11ad is a protocol used for very high data rates about 8 Gbit s and for short range communication about 1 10 meters 57 TP Link announced the world s first 802 11ad router in January 2016 58 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 Edit Main article IEEE 802 11af IEEE 802 11af also referred to as White Fi and Super Wi Fi 59 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 60 61 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 61 Access points and stations determine their position using a satellite positioning system such as GPS and use the Internet to query a geolocation database GDB provided by a regional regulatory agency to discover what frequency channels are available for use at a given time and position 61 The physical layer uses OFDM and is based on 802 11ac 62 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 61 The frequency channels are 6 to 8 MHz wide depending on the regulatory domain 61 Up to four channels may be bonded in either one or two contiguous blocks 61 MIMO operation is possible with up to four streams used for either space time block code STBC or multi user MU operation 61 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 37 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 37 802 11 2016 Edit IEEE 802 11 2016 which was known as IEEE 802 11 REVmc 63 is a revision based on IEEE 802 11 2012 incorporating 5 amendments 11ae 11aa 11ad 11ac 11af 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 64 802 11ah Edit Main article IEEE 802 11ah IEEE 802 11ah published in 2017 65 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 66 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 67 802 11ai Edit Main article IEEE 802 11ai IEEE 802 11ai is an amendment to the 802 11 standard that added new mechanisms for a faster initial link setup time 68 802 11aj Edit IEEE 802 11aj is a derivative of 802 11ad for use in the 45 GHz unlicensed spectrum available in some regions of the world specifically China it also provides additional capabilities for use in the 60 GHz band 68 Alternatively known as China Millimeter Wave CMMW 802 11aq Edit 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 discover further the services running on a device or provided by a network 68 802 11 2020 Edit IEEE 802 11 2020 which was known as IEEE 802 11 REVmd 69 is a revision based on IEEE 802 11 2016 incorporating 5 amendments 11ai 11ah 11aj 11ak 11aq 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 added 70 802 11ax Edit Main article IEEE 802 11ax IEEE 802 11ax is the successor to 802 11ac marketed as Wi Fi 6 2 4 GHz and 5 GHz 71 and Wi Fi 6E 6 GHz 72 by the Wi Fi Alliance It is also known as High Efficiency Wi Fi for the overall improvements to Wi Fi 6 clients under dense environments 73 For an individual client the maximum improvement in data rate PHY speed against the predecessor 802 11ac is only 39 a for comparison this improvement was nearly 500 b i for the predecessors c Yet even with this comparatively minor 39 figure the goal was to provide 4 times the throughput per area d of 802 11ac hence High Efficiency The motivation behind this goal was the deployment of WLAN in dense environments such as corporate offices shopping malls and dense residential apartments 73 This is achieved by means of a technique called OFDMA which is basically multiplexing in the frequency domain as opposed to spatial multiplexing as in 802 11ac This is equivalent to cellular technology applied into Wi Fi 73 qt The IEEE 802 11ax 2021 standard was approved on February 9 2021 76 77 802 11ay Edit Main article IEEE 802 11ay This section needs to be updated Please help update this article to reflect recent events or newly available information March 2015 IEEE 802 11ay is a standard that is being developed also called EDMG Enhanced Directional MultiGigabit PHY 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 and short range communications due to atmospheric oxygen absorption and inability to penetrate walls The peak transmission rate of 802 11ay is 40 Gbit s 78 The main extensions include channel bonding 2 3 and 4 MIMO up to 4 streams and higher modulation schemes The expected range is 300 500 m 79 802 11ba Edit IEEE 802 11ba Wake up Radio WUR Operation is an amendment to the IEEE 802 11 standard that enables energy efficient operation for data reception without increasing latency 80 The target active power consumption to receive a WUR packet is less than 1 milliwatt and supports data rates of 62 5 kbit s and 250 kbit s The WUR PHY uses MC OOK multicarrier OOK to achieve extremely low power consumption 81 802 11be Edit Main article IEEE 802 11be IEEE 802 11be Extremely High Throughput EHT is the potential next amendment to the 802 11 IEEE standard 82 and will likely be designated as Wi Fi 7 83 84 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 Edit Graphical representation of Wi Fi application specific UDP performance envelope 2 4 GHz band with 802 11g 1 Mbps 1 Mbit s 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 Graphical representation of Wi Fi application specific UDP performance envelope 2 4 GHz band with 802 11n with 40MHz This means that typically data frames pass an 802 11 WLAN medium and are being converted to 802 3 Ethernet or vice versa Due to the difference in the frame header lengths of these two media the application s packet size determines the speed of the data transfer This means applications that use small packets e g VoIP create dataflows with high overhead traffic i e a low goodput Other factors that contribute to the overall application data rate are the speed with which the application transmits the packets i e the data rate 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 85 86 The same references apply to the attached graphs that show measurements of UDP throughput Each represents an average UDP throughput please note that the error bars are there but barely visible due to the small variation of 25 measurements Each is with a specific packet size small or large and with a specific data rate 10 kbit s 100 Mbit s Markers for traffic profiles of common applications are included as well These figures assume there are no packet errors which if occurring will lower the transmission rate further Channels and frequencies EditSee also List of WLAN channels 802 11b 802 11g and 802 11n 2 4 utilize the 2 400 2 500 GHz spectrum one of the ISM bands 802 11a 802 11n and 802 11ac use the more heavily regulated 4 915 5 825 GHz 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 how 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 Graphical representation of Wi Fi channels in the 2 4 GHz band The channel numbering of the 5 725 5 875 GHz 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 Edit In addition to specifying the channel center frequency 802 11 also specifies in Clause 17 a spectral mask defining the permitted power distribution across each channel The mask requires the signal to be attenuated a minimum of 20 dB from its peak amplitude at 11 MHz from the center 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 1 13 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 87 88 North America and some Central and South American countries allow only 1 through 11 Spectral masks for 802 11g channels 1 14 in the 2 4 GHz band 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 the overlapping signal on any channel should be sufficiently attenuated to interfere with a transmitter on any other channel minimally given the separation between channels Due to the near far problem a transmitter can impact desensitize a receiver on a non overlapping channel but only if it is close to the victim receiver within a meter 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 DSSS modulation and utilized a channel bandwidth of 22 MHz resulting in three non overlapping channels 1 6 and 11 802 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 1 5 9 and 13 exist under 802 11g However this is not the case as per 17 4 6 3 Channel Numbering of operating channels of the IEEE Std 802 11 2012 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 89 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 which is permitted in Europe but not in North America is barely different from a three channel configuration but with an entire extra channel 90 91 802 11 non overlapping channels for 2 4GHz Covers 802 11b g n However overlap between channels with more narrow spacing e g 1 4 7 11 in North America may cause unacceptable degradation of signal quality and throughput particularly when users transmit near the boundaries of AP cells 92 Regulatory domains and legal compliance Edit 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 93 Domain codes are specified for the United States Canada ETSI Europe 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 citation needed 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 citation needed Layer 2 Datagrams EditThe datagrams are called frames Current 802 11 standards specify frame types for use in the 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 FCS Some frames may not have a payload Field Frame control Duration id Address 1 Address 2 Address 3 Sequence control Address 4 QoS control HT control Frame body Frame check sequenceLength Bytes 2 2 6 6 6 0 or 2 6 0 or 2 0 or 4 Variable 4The 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 Protocol Version Two bits representing the protocol version The currently used protocol version is zero Other values are reserved for future use Type Two bits identifying the type of WLAN frame Control Data and Management are various frame types defined in IEEE 802 11 Subtype Four bits providing additional discrimination between frames Type and Subtype are used together to identify the exact frame ToDS and FromDS Each is one bit in size They indicate whether a data frame is headed for a distribution system or it is getting out of it Control and management frames set these values to zero All the data frames will have one of these bits set ToDS 0 and FromDS 0 Communication within a basic service set or an independent basic service set IBSS network ToDS 0 and FromDS 1 A frame sent by a station and directed to an AP accessed via the distribution system ToDS 1 and FromDS 0 A frame exiting the distribution system for a station ToDS 1 and FromDS 1 Only kind of frame frame that uses all four MAC addresses in a DATA frame Address 1 final station address Address 2 access point address exiting from the distribution system Address 3 access point entrance to the distribution system AP to which the source station is connected Address 4 address of the source station 94 More Fragments The More Fragments bit is set when a packet is divided into multiple frames for transmission Every frame except the last frame of a packet will have this bit set Retry Sometimes frames require retransmission and for this there is a Retry bit that is set to one when a frame is resent This aids in the elimination of duplicate frames Power Management This bit indicates the power management state of the sender after the completion of a frame exchange Access points are required to manage the connection and will never set the power saver bit More Data The More Data bit is used to buffer frames received in a distributed system The access point uses this bit to facilitate stations in power saver mode It indicates that at least one frame is available and addresses all stations connected Protected Frame The Protected Frame bit is set to the value of one if the frame body is encrypted by a protection mechanism such as Wired Equivalent Privacy WEP Wi Fi Protected Access WPA or Wi Fi Protected Access II WPA2 Order This bit is set only when the strict ordering delivery method is employed Frames and fragments are not always sent in order as it causes a transmission performance penalty The next two bytes are reserved for the Duration ID field indicating 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 CFP and Association ID AID 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 dubious discuss 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 Sequence Control field is a two byte section used to identify message order and eliminate duplicate frames The first 4 bits are used for the fragmentation number and the last 12 bits are the sequence number An optional two byte Quality of Service control field present in QoS Data frames it was added with 802 11e 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 FCS is the last four bytes in the standard 802 11 frame Often referred to as the Cyclic Redundancy Check CRC it allows for integrity checks 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 95 Management frames Edit Management frames are not always authenticated and allow for the maintenance or discontinuance of communication Some common 802 11 subtypes include Authentication frame 802 11 authentication begins with the wireless network interface card WNIC sending an authentication frame to the access point containing its identity When open system authentication is being used the WNIC sends only a single authentication frame and the access point responds with an authentication frame of its own indicating acceptance or rejection When shared key authentication is being used the WNIC sends an initial authentication request and the access point responds with an authentication frame containing challenge text The WNIC then sends an authentication frame containing the encrypted version of the challenge text to the access point The access point ensures the text was encrypted with the correct key by decrypting it with its own key The result of this process determines the WNIC s authentication status Association request frame Sent from a station it enables the access point to allocate resources and synchronize The frame carries information about the WNIC including supported data rates and the SSID of the network the station wishes to associate with If the request is accepted the access point reserves memory and establishes an association ID for the WNIC Association response frame Sent from an access point to a station containing the acceptance or rejection to an association request If it is an acceptance the frame will contain information such as an association ID and supported data rates Beacon frame Sent periodically from an access point to announce its presence and provide the SSID and other parameters for WNICs within range Deauthentication frame Sent from a station wishing to terminate connection from another station Disassociation frame Sent from a station wishing to terminate the connection It is an elegant way to allow the access point to relinquish memory allocation and remove the WNIC from the association table Probe request frame Sent from a station when it requires information from another station Probe response frame Sent from an access point containing capability information supported data rates etc after receiving a probe request frame Reassociation request frame A WNIC sends a reassociation request when it drops from the currently associated access point range and finds another access point with a stronger signal The new access point coordinates the forwarding of any information that may still be contained in the buffer of the previous access point Reassociation response frame Sent from an access point containing the acceptance or rejection to a WNIC reassociation request frame The frame includes information required for association such as the association ID and supported data rates Action frame extending management frame to control a certain action Some of the action categories are Block Ack Radio Measurement Fast BSS Transition etc These frames are sent by a station when it needs to tell its peer for a certain action to be taken For example a station can tell another station to set up a block acknowledgement by sending an ADDBA Request action frame The other station would then respond with an ADDBA Response action frame The body of a management frame consists of frame subtype dependent fixed fields followed by a sequence of information elements IEs The common structure of an IE is as follows Field Type Length DataLength 1 1 1 252Control frames Edit Control frames facilitate the exchange of data frames between stations Some common 802 11 control frames include Acknowledgement ACK frame After receiving a data frame the receiving station will send an ACK frame to the sending station if no errors are found If the sending station doesn t receive an ACK frame within a predetermined period of time the sending station will resend the frame Request to Send RTS frame The RTS and CTS frames provide an optional collision reduction scheme for access points with hidden stations A station sends an RTS frame as the first step in a two way handshake required before sending data frames Clear to Send CTS frame A station responds to an RTS frame with a CTS frame It provides clearance for the requesting station to send a data frame The CTS provides collision control management by including a time value for which all other stations are to hold off transmission while the requesting station transmits Data frames Edit Data frames carry packets from web pages files etc within the body 96 The body begins with an IEEE 802 2 header with the Destination Service Access Point DSAP specifying the protocol followed by a Subnetwork Access Protocol SNAP header if the DSAP is hex AA with the organizationally unique identifier OUI and protocol ID PID fields specifying the protocol If the OUI is all zeroes the protocol ID field is an EtherType value 97 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 Access points varies 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 98 It is important to be aware that the link layer should recover these lost frames If the sender does not receive an Acknowledgement ACK frame then it will be resent Standards and amendments EditWithin the IEEE 802 11 Working Group 60 the following IEEE Standards Association Standard and Amendments exist IEEE 802 11 1997 The WLAN standard was originally 1 Mbit s and 2 Mbit s 2 4 GHz RF and infrared IR standard 1997 all the others listed below are Amendments to this standard except for Recommended Practices 802 11F and 802 11T IEEE 802 11a 54 Mbit s 5 GHz standard 1999 shipping products in 2001 IEEE 802 11b 5 5 Mbit s and 11 Mbit s 2 4 GHz standard 1999 IEEE 802 11c Bridge operation procedures included in the IEEE 802 1D standard 2001 IEEE 802 11d International country to country roaming extensions 2001 IEEE 802 11e Enhancements QoS including packet bursting 2005 IEEE 802 11F Inter Access Point Protocol 2003 Withdrawn February 2006 IEEE 802 11g 54 Mbit s 2 4 GHz standard backwards compatible with b 2003 IEEE 802 11h Spectrum Managed 802 11a 5 GHz for European compatibility 2004 IEEE 802 11i Enhanced security 2004 IEEE 802 11j Extensions for Japan 4 9 5 0 GHz 2004 IEEE 802 11 2007 A new release of the standard that includes amendments a b d e g h i and j July 2007 IEEE 802 11k Radio resource measurement enhancements 2008 IEEE 802 11n Higher Throughput WLAN at 2 4 and 5 GHz 20 and 40 MHz channels introduces MIMO to Wi Fi September 2009 IEEE 802 11p WAVE Wireless Access for the Vehicular Environment such as ambulances and passenger cars July 2010 IEEE 802 11r Fast BSS transition FT 2008 IEEE 802 11s Mesh Networking Extended Service Set ESS July 2011 IEEE 802 11T Wireless Performance Prediction WPP test methods and metrics Recommendation cancelled IEEE 802 11u Improvements related to HotSpots and 3rd party authorization of clients e g cellular network offload February 2011 IEEE 802 11v Wireless network management February 2011 IEEE 802 11w Protected Management Frames September 2009 IEEE 802 11y 3650 3700 MHz Operation in the U S 2008 IEEE 802 11z Extensions to Direct Link Setup DLS September 2010 IEEE 802 11 2012 A new release of the standard that includes amendments k n p r s u v w y and z March 2012 IEEE 802 11aa Robust streaming of Audio Video Transport Streams June 2012 see Stream Reservation Protocol IEEE 802 11ac Very High Throughput WLAN at 5 GHz e wider channels 80 and 160 MHz Multi user MIMO down link only 99 December 2013 IEEE 802 11ad Very High Throughput 60 GHz December 2012 see also WiGig IEEE 802 11ae Prioritization of Management Frames March 2012 IEEE 802 11af TV Whitespace February 2014 IEEE 802 11 2016 A new release of the standard that includes amendments aa ac ad ae and af December 2016 IEEE 802 11ah Sub 1 GHz license exempt operation e g sensor network smart metering December 2016 IEEE 802 11ai Fast Initial Link Setup December 2016 IEEE 802 11aj China Millimeter Wave February 2018 IEEE 802 11ak Transit Links within Bridged Networks June 2018 IEEE 802 11aq Pre association Discovery July 2018 IEEE 802 11 2020 A new release of the standard that includes amendments ah ai aj ak and aq December 2020 IEEE 802 11ax High Efficiency WLAN at 2 4 5 and 6 GHz f introduces OFDMA to Wi Fi 73 February 2021 IEEE 802 11ay Enhancements for Ultra High Throughput in and around the 60 GHz Band March 2021 IEEE 802 11az Next Generation Positioning March 2023 IEEE 802 11ba Wake Up Radio March 2021 IEEE 802 11bd Enhancements for Next Generation V2X see also IEEE 802 11p March 2023 In process Edit IEEE 802 11bb Light Communications Dec 2023 IEEE 802 11bc Enhanced Broadcast Service Dec 2023 IEEE 802 11be Extremely High Throughput see also IEEE 802 11ax May 2024 IEEE 802 11bf WLAN Sensing IEEE 802 11bh Randomized and Changing MAC Addresses IEEE 802 11bi Enhanced Data Privacy IEEE 802 11bk 320 MHz Positioning IEEE 802 11me 802 11 Accumulated Maintenance Changes802 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 802 11mc for 802 11 2016 and 802 11md for 802 11 2020 Standard vs amendment Edit Both the terms standard and amendment are used when referring to the different variants of IEEE standards 100 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 published IEEE 802 11 2020 is the only version currently in publication superseding previous releases The standard is updated by means of amendments Amendments are created by task groups TG Both the task group and their finished document are denoted by 802 11 followed by one or two lower case letters for example IEEE 802 11a or IEEE 802 11ax 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 2016 and 2020 101 102 Nomenclature EditVarious 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 usually abbreviated TU is used to indicate a unit of time equal to 1024 microseconds Numerous time constants are defined in terms of TU rather than the nearly equal millisecond 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 EditIn 2001 a group from the University of California Berkeley presented a paper describing weaknesses in the 802 11 Wired Equivalent Privacy WEP 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 amp 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 103 The IEEE set up a dedicated task group to create a replacement security solution 802 11i previously this work was handled as part of a broader 802 11e effort to enhance the MAC layer The Wi Fi Alliance announced an interim specification called Wi Fi Protected Access WPA based on a subset of the then current IEEE 802 11i draft These started to appear in products in mid 2003 IEEE 802 11i also known as WPA2 itself was ratified in June 2004 and uses the Advanced Encryption Standard AES instead of RC4 which was used in WEP The modern recommended encryption for the home consumer space is WPA2 AES Pre Shared Key and for the enterprise space is WPA2 along with a RADIUS authentication server or another type of authentication server and a strong authentication method such as EAP TLS citation needed 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 104 In December 2011 a security flaw was revealed that affects some wireless routers with a specific implementation of the optional Wi Fi Protected Setup WPS 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 105 106 In late 2014 Apple announced that its iOS 8 mobile operating system would scramble MAC addresses 107 during the pre association stage to thwart retail footfall tracking made possible by the regular transmission of uniquely identifiable probe requests citation needed Wi Fi users may be subjected to a Wi Fi deauthentication attack to eavesdrop attack passwords or force the use of another usually more expensive access point 108 See also Edit802 11 Frame Types Comparison of wireless data standards Fujitsu Ltd v Netgear Inc Gi Fi a term used by some trade press to refer to faster versions of the IEEE 802 11 standards LTE WLAN Aggregation OFDM system comparison table TU time unit TV White Space Database Ultra wideband White spaces radio Wi Fi operating system support Wibree or Bluetooth low energy WiGig Wireless USB another wireless protocol primarily designed for shorter range applicationsNotes Edit 802 11ax with 2402 Mbit s MCS Index 11 2 spatial streams 160 MHz versus 802 11ac with 1733 3 Mbit s MCS Index 9 2 spatial streams 160 MHz 74 802 11ac with 1733 3 Mbit s MCS Index 9 2 spatial streams 160 MHz versus 802 11n with 300 Mbit s MCS Index 7 2 spatial streams 40 MHz An IEEE article considers only a 37 growth for 802 11ax and a 1000 growth for both 802 11ac and 802 11n 73 Throughput per area as defined by IEEE is the ratio of the total network throughput to the network area 73 Operation in the 2 4 GHz band is specified by 802 11n 6 GHz operation only between Wi Fi 6E devices This improvement is 1100 if we consider 144 4 Mbit s MCS Index 15 2 spatial streams 20 MHz due to 40 MHz mode from 802 11n at 2 4 GHz having little practical use in most scenarios 75 qt 74 Footnotes Edit a b IEEE SA Standards Board Operations Manual IEEE SA Archived from the original on 6 September 2015 Retrieved 13 September 2015 ARRLWeb Part 97 Amateur Radio Service American Radio Relay League Archived from the original on 9 March 2010 Retrieved 27 September 2010 MCS table updated with 80211ax data rates semfionetworks com Wi Fi 6E only specifies operation in the 6 GHz band Operation in the 5 and 2 4 GHz bands is specified by Wi Fi 6 802 11ac only specifies operation in the 5 GHz band Operation in the 2 4 GHz band is specified by 802 11n Kastrenakes Jacob 3 October 2018 Wi Fi Now Has Version Numbers and Wi Fi 6 Comes Out Next Year The Verge Retrieved 2 May 2019 Wi Fi Generation Numbering ElectronicNotes Retrieved 10 November 2021 Phillips Gavin 18 January 2021 The Most Common Wi Fi Standards and Types Explained MUO Make Use Of Archived from the original on 11 November 2021 Retrieved 9 November 2021 Wi Fi Generation Numbering ElectronicsNotes Archived from the original on 11 November 2021 Retrieved 10 November 2021 Wi Fi CERTIFIED 6 Wi Fi Alliance www wi fi org Retrieved 2 May 2019 Kastrenakes Jacob 3 October 2018 Wi Fi now has version numbers and Wi Fi 6 comes out next year The Verge Retrieved 2 May 2019 Wolter Lemstra Vic Hayes John Groenewegen 2010 The Innovation Journey of Wi Fi The Road To Global Success Cambridge University Press ISBN 978 0 521 19971 1 Ben Charny 6 December 2002 Vic Hayes Wireless Vision CNET Archived from the original on 26 August 2012 Retrieved 30 April 2011 Hetting Claus 8 November 2019 Vic Hayes amp Bruce Tuch inducted into the Wi Fi 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January 2012 US CERT Vulnerability Note VU 723755 Archived 2012 01 03 at the Wayback Machine iOS 8 strikes an unexpected blow against location tracking 9 June 2014 Archived from the original on 2 April 2015 Harnesk Saga Finding vulnerabilities in connected devices PDF KTH Royal Institute of Technology References EditIEEE 802 11 Wireless LAN Medium Access Control MAC and Physical Layer PHY Specifications 2016 revision IEEE SA 14 December 2016 doi 10 1109 IEEESTD 2016 7786995 ISBN 978 1 5044 3645 8 IEEE 802 11k 2008 Amendment 1 Radio Resource Measurement of Wireless LANs PDF IEEE SA 12 June 2008 doi 10 1109 IEEESTD 2008 4544755 ISBN 978 0 7381 5420 6 IEEE 802 11r 2008 Amendment 2 Fast Basic Service Set BSS Transition PDF IEEE SA 15 July 2008 doi 10 1109 IEEESTD 2008 4573292 ISBN 978 0 7381 5422 0 IEEE 802 11y 2008 Amendment 3 3650 3700 MHz Operation in USA PDF IEEE SA 6 November 2008 doi 10 1109 IEEESTD 2008 4669928 ISBN 978 0 7381 5765 8 External links EditIEEE 802 11 working group 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