802.11 is a set of media access control (MAC) and physical layer
(PHY) specifications for implementing wireless local area network
(WLAN) computer communication in the 900 MHz and 2.4, 3.6, 5, and
60 GHz frequency bands. They are the world's most widely used
wireless computer networking standards, used in most home and office
networks to allow laptops, printers, and smartphones to talk to each
other and access the
Internet without connecting wires. They are
created and maintained by the Institute of Electrical and Electronics
Engineers (IEEE) LAN/MAN Standards Committee (
IEEE 802). The base
version of the standard was released in 1997, and has had subsequent
amendments. The standard and amendments provide the basis for wireless
network products using the
Wi-Fi brand. While each amendment is
officially revoked when it is incorporated in the latest version of
the standard, the corporate world tends to market to the revisions
because they concisely denote capabilities of their products. As a
result, in the marketplace, each revision tends to become its own
1 General description
3.1 802.11-1997 (
3.2 802.11a (
4 Common misunderstandings about achievable throughput
5 Channels and frequencies
5.1 Channel spacing within the 2.4 GHz band
5.2 Regulatory domains and legal compliance
6 Layer 2 – Datagrams
6.1 Management frames
6.2 Control frames
6.3 Data frames
7 Standards and amendments
7.1 In process
7.2 Standard vs. amendment
9 Community networks
802.11 extensions and equipment
12 See also
15 External links
802.11 family consists of a series of half-duplex over-the-air
modulation techniques that use the same basic protocol. 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 may also include corrections to a previous
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. Because of this choice of frequency
band, 802.11b and g equipment may occasionally suffer interference
from microwave ovens, cordless telephones, and
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 channels rather than
the 2.4 GHz ISM frequency band offering only three
non-overlapping 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 can use either the 2.4 GHz or the 5 GHz
band; 802.11ac uses only the 5 GHz band.
The segment of the radio frequency spectrum used by
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.
802.11 technology has its origins in a 1985 ruling by the U.S. Federal
Communications Commission that released the ISM band for unlicensed
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
WaveLAN with raw data rates of 1 Mbit/s and
Vic Hayes, who held the chair of
802.11 for 10 years, and has
been called the "father of Wi-Fi", was involved in designing the
initial 802.11b and 802.11a standards within the IEEE.
In 1999, the
Wi-Fi Alliance was formed as a trade association to hold
Wi-Fi trademark under which most products are sold.
802.11 network PHY standards
Stream data rate
20 m (66 ft)
100 m (330 ft)
6, 9, 12, 18, 24, 36, 48, 54
35 m (115 ft)
120 m (390 ft)
5,000 m (16,000 ft)[A]
1, 2, 5.5, 11
35 m (115 ft)
140 m (460 ft)
6, 9, 12, 18, 24, 36, 48, 54
38 m (125 ft)
140 m (460 ft)
Up to 288.8[B]
70 m (230 ft)
250 m (820 ft)
Up to 600[B]
Up to 346.8[B]
35 m (115 ft)
Up to 800[B]
Up to 1733.2[B]
Up to 3466.8[B]
Up to 568.9
Up to 6,757
OFDM, single carrier,
low-power single carrier
3.3 m (11 ft)
Up to 347 
Est. Jul 2017
Est. Dec 2018
Up to 10.53 Gbit/s
Est. Nov 2019
Up to 20,000 (20 Gbit/s) 
OFDM, single carrier,
10 m (33 ft)
100 m (328 ft)
Est. Mar 2021
802.11 Standard rollups
Up to 54
Up to 150[B]
2.4, 5, 60
Up to 866.7 or 6,757[B]
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.
IEEE 802.11af about using white space spectrum for WiFi based on
the PHY layer of 802.11ac
802.11 (legacy mode)
The original version of the standard
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.
802.11 with direct-sequence spread spectrum was rapidly
supplanted and popularized by 802.11b.
Originally described as clause 17 of the 1999 specification, the OFDM
waveform at 5.8 GHz is now defined in clause 18 of the 2012
specification, and provides protocols that allow transmission and
reception of data at rates of 1.5 to 54 Mbit/s. It has seen
widespread worldwide implementation, particularly within the corporate
workspace. While the original amendment is no longer valid, the term
802.11a is still used by wireless access point (cards and routers)
manufacturers to describe interoperability of their systems at
5 GHz, 54 Mbit/s.
The 802.11a standard uses the same data link layer protocol and frame
format as the original standard, but an
OFDM based air interface
(physical layer). 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.
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, but locally there may be fewer signals to interfere
with, resulting in less interference and better throughput.
The 802.11b standard has a maximum raw data rate of 11 Mbit/s,
and uses the same media access method defined in the original
standard. 802.11b products appeared on the market in early 2000, since
802.11b is a direct extension of the modulation technique defined in
the original standard. The dramatic increase in throughput of 802.11b
(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.
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.
802.11g hardware is fully backward compatible with 802.11b hardware,
and therefore is encumbered with legacy issues that reduce throughput
by ~21% when compared to 802.11a.
The then-proposed 802.11g standard was rapidly adopted in the market
starting in January 2003, well before ratification, due to the desire
for higher data rates as well as to reductions in manufacturing costs.
By summer 2003, most dual-band 802.11a/b products became
dual-band/tri-mode, supporting a and b/g in a single mobile adapter
card or access point. Details of making b and g work well together
occupied much of the lingering technical process; in an 802.11g
network, however, activity of an 802.11b participant will reduce the
data rate of the overall 802.11g network.
Like 802.11b, 802.11g devices suffer interference from other products
operating in the 2.4 GHz band, for example wireless keyboards.
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 March 8, 2007, 802.11REVma was renamed to the then-current
802.11n is an amendment that improves upon the previous 802.11
standards by adding 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. 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.
In May 2007, task group TGmb was authorized to "roll up" many of the
amendments to the 2007 version of the
802.11 standard. REVmb or
802.11mb, as it was called, created a single document that merged ten
amendments (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. Upon publication on March 29, 2012, the new
standard was referred to as
IEEE 802.11ac-2013 is an amendment to
IEEE 802.11, published in
December 2013, that builds on 802.11n. 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
MIMO (MU-MIMO). As of October 2013, high-end
implementations support 80 MHz channels, three spatial streams,
and 256-QAM, yielding a data rate of up to 433.3 Mbit/s per
spatial stream, 1300 Mbit/s total, in 80 MHz channels in the
5 GHz band. Vendors have announced plans to release so-called
"Wave 2" devices with support for 160 MHz channels, four spatial
streams, and MU-
MIMO in 2014 and 2015.
This section needs to be updated. Please update this article to
reflect recent events or newly available information. (November 2013)
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
WiGig Alliance. The peak transmission rate of 802.11ad
is 7 Gbit/s.
TP-Link announced the world's first
802.11ad router in January
IEEE 802.11af, also referred to as "White-Fi" and "Super Wi-Fi",
is an amendment, approved in February 2014, that allows WLAN operation
in TV white space spectrum in the
UHF bands between 54 and
790 MHz. It uses cognitive radio technology to transmit
on unused TV channels, with the standard taking measures to limit
interference for primary users, such as analog TV, digital TV, and
wireless microphones. Access points and stations determine their
position using a satellite positioning system such as GPS, and use the
Internet to query a geolocation database (GDB) provided by a regional
regulatory agency to discover what frequency channels are available
for use at a given time and position. The physical layer uses OFDM
and is based on 802.11ac. The propagation path loss as well as the
attenuation by materials such as brick and concrete is lower in the
VHF bands than in the 2.4 and 5 GHz bands, which
increases the possible range. The frequency channels are 6 to
8 MHz wide, depending on the regulatory domain. Up to four
channels may be bonded in either one or two contiguous blocks.
MIMO operation is possible with up to four streams used for either
space–time block code (STBC) or multi-user (MU) operation. The
achievable data rate per spatial stream is 26.7 Mbit/s for 6 and
7 MHz channels, and 35.6 Mbit/s for 8 MHz channels.
With four spatial streams and four bonded channels, the maximum data
rate is 426.7 Mbit/s for 6 and 7 MHz channels and
568.9 Mbit/s for 8 MHz channels.
802.11ag refers to 802.11a and 802.11g operating simultaneously
IEEE 802.11ah defines a WLAN system operating at sub-1 GHz
license-exempt bands, with final approval slated for September
2016. Due to the favorable propagation characteristics of the
low frequency spectra, 802.11ah can provide improved transmission
range compared with the conventional
802.11 WLANs operating in the
2.4 GHz and 5 GHz bands. 802.11ah can be used for
various purposes including large scale sensor networks, extended
range hotspot, and outdoor
Wi-Fi for cellular traffic offloading,
whereas the available bandwidth is relatively narrow. The protocol
intends consumption to be competitive with low power Bluetooth, at a
much wider range.
IEEE 802.11ai is an amendment to the
802.11 standard that added new
mechanisms for a faster initial link setup time.
IEEE 802.11aj is a rebanding of
802.11ad for use in the 45 GHz
unlicensed spectrum available in some regions of the world
IEEE 802.11aq is an amendment to the
802.11 standard that will enable
pre-association discovery of services. This extends some of the
mechanisms in 802.11u that enabled device discovery to further
discover the services running on a device, or provided by a
IEEE 802.11ax is the successor to 802.11ac, and will increase the
efficiency of WLAN networks. Currently in development, this project
has the goal of providing 4x the throughput of 802.11ac.
This section needs to be updated. Please update this article to
reflect recent events or newly available information. (March 2015)
IEEE 802.11ay is a standard that is being developed. It is an
amendment that defines a new physical layer for
802.11 networks to
operate in the 60 GHz millimeter wave spectrum. It will be an
extension of the existing 11ad, aimed to extend the throughput, range
and use-cases. The main use-cases include: indoor operation, out-door
back-haul and short range communications. The peak transmission rate
of 802.11ay is 20 Gbit/s. The main extensions include:
channel bonding (2, 3 and 4),
MIMO and higher modulation schemes.
IEEE 802.11-2016 is a revision based on
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.
Common misunderstandings about achievable throughput
Graphical representation of
Wi-Fi application specific (UDP)
performance envelope 2.4 GHz band, with 802.11g
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
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.
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 transmission rate
Channels and frequencies
See 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 the way radio and TV broadcast
bands are sub-divided.
The 2.4 GHz band is divided into 14 channels spaced 5 MHz
apart, beginning with channel 1, which is centered on
2.412 GHz. The latter channels have additional restrictions or
are unavailable for use in some regulatory domains.
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,
specifies (in Clause 17) a spectral mask defining the permitted power
distribution across each channel. The mask requires the signal be
attenuated a minimum of 20 dB from its peak amplitude at
±11 MHz from the centre frequency, the point at which a channel
is effectively 22 MHz wide. One consequence is that stations can
use only every fourth or fifth channel without overlap.
Availability of channels is regulated by country, constrained in part
by how each country allocates radio spectrum to various services. At
Japan permits the use of all 14 channels for 802.11b, and
1–13 for 802.11g/n-2.4. Other countries such as
allowed only channels 10 and 11, and
France allowed only 10, 11, 12,
and 13; however, they now allow channels 1 through 13. North
America and some Central and South American countries allow only 1
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,
given the separation between channels, the overlapping signal on any
channel should be sufficiently attenuated to minimally interfere with
a transmitter on any other channel. Due to the near-far problem a
transmitter can impact (desense) 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.
Confusion often arises over the amount of channel separation required
between transmitting devices. 802.11b was based on 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, although this is not the case
as per 188.8.131.52 Channel Numbering of operating channels of the IEEE
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." and section 184.108.40.206 and
This does not mean that the technical overlap of the channels
recommends the non-use of overlapping channels. The amount of
interference seen on a configuration using channels 1, 5, 9, and 13
can have very small difference from a three-channel configuration,
and in the paper entitled "Effect of adjacent-channel interference in
802.11 WLANs" by Villegas this is also demonstrated.
802.11 non-overlapping channels for 2.4GHz. Covers 802.11b,g,n
Although the statement that channels 1, 5, 9, and 13 are
"non-overlapping" is limited to spacing or product density, the
concept has some merit in limited circumstances.
Special care must be
taken to adequately space AP cells, since overlap between the channels
may cause unacceptable degradation of signal quality and
throughput. If more advanced equipment such as spectral analyzers
are available, overlapping channels may be used under certain
circumstances. This way, more channels are available.
Regulatory domains and legal compliance
IEEE uses the phrase regdomain to refer to a legal regulatory region.
Different countries define different levels of allowable transmitter
power, time that a channel can be occupied, and different available
channels. Domain codes are specified for the United States,
Canada, ETSI (Europe), Spain, France, Japan, and China.
Wi-Fi certified devices default to regdomain 0, which means least
common denominator settings, i.e., the device will not transmit at a
power above the allowable power in any nation, nor will it use
frequencies that are not permitted in any nation.
The regdomain setting is often made difficult or impossible to change
so that the end users do not conflict with local regulatory agencies
such as the United States' Federal Communications Commission.
Layer 2 – Datagrams
The datagrams are called frames. Current
802.11 standards specify
frame types for use in transmission of data as well as management and
control of wireless links.
Frames are divided into very specific and standardized sections. Each
frame consists of a MAC header, payload, and frame check sequence
(FCS). Some frames may not have a payload.
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.
Currently used protocol version is zero. Other values are reserved for
Type: Two bits identifying the type of WLAN frame. Control, Data, and
Management are various frame types defined in
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. Control and management
frames set these values to zero. All the data frames will have one of
these bits set. However communication within an independent basic
service set (IBSS) network always set these bits to zero.
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
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 one if the frame
body is encrypted by a protection mechanism such as Wired Equivalent
Wi-Fi Protected Access (WPA), or Wi-FI Protected Access
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. This field
can take one of three forms: Duration, Contention-Free Period (CFP),
and Association ID (AID).
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 for identifying
message order as well as eliminating 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 check of retrieved frames. As frames are about
to be sent, the FCS is calculated and appended. When a station
receives a frame, it can calculate the FCS of the frame and compare it
to the one received. If they match, it is assumed that the frame was
not distorted during transmission.
Management frames are not always authenticated, and allow for the
maintenance, or discontinuance, of communication. Some common 802.11
802.11 authentication begins with the wireless
network interface card (WNIC) sending an authentication frame to the
access point containing its identity. With an open system
authentication, the WNIC sends only a single authentication frame, and
the access point responds with an authentication frame of its own
indicating acceptance or rejection. With shared key authentication,
after the WNIC sends its initial authentication request it will
receive an authentication frame from the access point containing
challenge text. The WNIC 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 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
Deauthentication frame: Sent from a station wishing to terminate
connection from another station.
Disassociation frame: Sent from a station wishing to terminate
connection. It's an elegant way to allow the access point to
relinquish memory allocation and remove the WNIC from the association
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
Reassociation request frame: A WNIC sends a reassociation request when
it drops from range of the currently associated access point 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.
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:
← 1 → ← 1 → ← 1-252 →
Type Length Data
Control frames facilitate in 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
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 a 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 carry packets from web pages, files, etc. within the
body. The body begins with an
IEEE 802.2 header, with the
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. Almost all
frames use 802.2 and SNAP headers, and most use an OUI of 00:00:00 and
TCP congestion control on the internet, frame loss is built
into the operation of 802.11. To select the correct transmission speed
Modulation and Coding Scheme, a rate control algorithm may test
different speeds. The actual packet loss rate of an Access points vary
widely for different link conditions. There are variations in the loss
rate experienced on production Access points, between 10% and 80%,
with 30% being a common average. It is important to be aware that
the link layer should recover these lost frames. If the sender does
not receive an Acknowledgement (ACK) frame, then it will be resent.
Standards and amendments
802.11 Working Group, the following
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: Enhancements to
802.11 to support 5.5 Mbit/s and
11 Mbit/s (1999)
IEEE 802.11c: Bridge operation procedures; included in the
IEEE 802.11d: International (country-to-country) roaming extensions
IEEE 802.11e: Enhancements: QoS, including packet bursting (2005)
Inter-Access Point Protocol (2003) Withdrawn February
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
IEEE 802.11i: Enhanced security (2004)
IEEE 802.11j: Extensions for
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 improvements using MIMO
(multiple-input, multiple-output antennas) (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
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
IEEE 802.11ac: Very High Throughput <6 GHz; potential
improvements over 802.11n: better modulation scheme (expected ~10%
throughput increase), wider channels (estimate in future time 80 to
160 MHz), multi user MIMO; (December 2013)
IEEE 802.11ad: Very High Throughput 60 GHz (December 2012) —
IEEE 802.11ae: Prioritization of Management Frames (March 2012)
IEEE 802.11af: TV Whitespace (February 2014)
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 802.11-2016: A new release of the standard that includes
amendments ae, aa, ad, ac, and af (December 2016)
China Millimeter Wave (~ December 2017 for RevCom
IEEE 802.11ak: General Links (~ March 2018 for RevCom approval)
IEEE 802.11aq: Pre-association Discovery (~ March 2018 for RevCom
IEEE 802.11ax: High Efficiency WLAN (~ December 2019 for RevCom
IEEE 802.11ay: Enhancements for Ultra High Throughput in and around
the 60 GHz Band (~ November 2019 for final EC approval)
IEEE 802.11az: Next Generation Positioning (~ March 2021 for .11az
IEEE 802.11ba: Wake Up Radio (~ July 2020 for RevCom submittal)
802.11F and 802.11T are recommended practices rather than standards,
and are capitalized as such.
802.11m is used for standard maintenance. 802.11ma was completed for
802.11-2007, 802.11mb for 802.11-2012, and 802.11mc for 802.11-2016.
Standard vs. amendment
Both the terms "standard" and "amendment" are used when referring to
the different variants of
As far as the
IEEE Standards Association is concerned, there is only
one current standard; it is denoted by
802.11 followed by the
date that it was published.
IEEE 802.11-2016 is the only version
currently in publication, superseding previous releases. The standard
is updated by means of amendments. Amendments are created by task
groups (TG). Both the task group and their finished document are
802.11 followed by a non-capitalized letter, for example,
IEEE 802.11a and
IEEE 802.11b. Updating
802.11 is the responsibility
of task group m. In order to create a new version, TGm combines the
previous version of the standard and all published amendments. TGm
also provides clarification and interpretation to industry on
published documents. New versions of the
802.11 were published in
1999, 2007, 2012, and 2016.
Various terms in
802.11 are used to specify aspects of wireless
local-area networking operation, and may be unfamiliar to some
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
802.11 LAN STAs.
With the proliferation of cable modems and DSL, there is an
ever-increasing market of people who wish to establish small networks
in their homes to share their broadband
Many hotspot or free networks frequently allow anyone within range,
including passersby outside, to connect to the Internet. There are
also efforts by volunteer groups to establish wireless community
networks to provide free wireless connectivity to the public.
In 2001, a group from the
University of California, Berkeley
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.
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
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
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.
In January 2005, the
IEEE set up yet another task group "w" to protect
management and broadcast frames, which previously were sent unsecured.
Its standard was published in 2009.
In December 2011, a security flaw was revealed that affects some
wireless routers with a specific implementation of the optional Wi-Fi
Protected Setup (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
In late 2014, Apple announced that its iOS 8 mobile operating
system would scramble MAC addresses during the pre-association
stage to thwart retail footfall tracking made possible by the regular
transmission of uniquely identifiable probe requests.
802.11 extensions and equipment
802.11 non-standard equipment
Many companies implement wireless networking equipment with non-IEEE
802.11 extensions either by implementing proprietary or draft
features. These changes may lead to incompatibilities between these
Comparison of wireless data standards
Fujitsu Ltd. v.
Gi-Fi, a term used by some trade press to refer to faster versions of
OFDM system comparison table
TU (time unit)
TV White Space Database
White spaces (radio)
Wi-Fi operating system support
Bluetooth low energy
Wireless Gigabit Alliance
Wireless Gigabit Alliance – also known as WiGig
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802.11 working group
Official timelines of
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List of all
Wi-Fi Chipset Vendors – Including historical timeline of
mergers and acquisitions
d · e
IEEE Standards Association
Spread spectrum in digital communications
Code-division multiple access
Code-division multiple access (CDMA)
Spread spectrum methods
Direct-sequence spread spectrum
Direct-sequence spread spectrum (DSSS)
Frequency-hopping spread spectrum
Frequency-hopping spread spectrum (FHSS)
Chirp spread spectrum
Chirp spread spectrum (CSS)
Time-hopping spread spectrum (THSS)
Space Network (NASA)
Cordless phones: DECT
IS-95 (aka cdmaOne)
CDMA2000 (aka IS-2000)
PN (pseudorandom noise) code
Power spectral density (PSD)
Low probability of intercept