IEEE 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 2.4, 3.6, 5 and 60 GHz frequency bands. They are created and maintained by the 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 market place, each revision tends to become its own standard.
- 1 General description
- 2 History
- 3 Protocol
- 4 Channels and frequencies
- 5 Layer 2 – Datagrams
- 6 Standard and amendments
- 7 Nomenclature
- 8 Community networks
- 9 Security
- 10 Non-standard 802.11 extensions and equipment
- 11 See also
- 12 References
- 13 External links
The 802.11 family consist of a series of half-duplex over-the-air modulation techniques that use the same basic protocol. The most popular are those defined by the 802.11b and 802.11g protocols, which are amendments to the original standard. 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 and 802.11g. 802.11n is a new multi-streaming modulation technique. Other standards in the family (c–f, h, j) are service amendments and extensions or corrections to the previous specifications.
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 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 channels rather than the 2.4 GHz ISM frequency band, where 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.
The segment of the radio frequency spectrum used by 802.11 varies between countries. In the US, 802.11a and 802.11g devices may be operated without a license, as allowed in Part 15 of the FCC Rules and Regulations. Frequencies used by channels one through six of 802.11b and 802.11g fall within the 2.4 GHz amateur radio band. Licensed amateur radio operators may operate 802.11b/g devices under Part 97 of the FCC Rules and Regulations, allowing increased power output but not commercial content or encryption.
In 1991 NCR Corporation/AT&T (now Alcatel-Lucent and LSI Corporation) invented the 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.
|Parts of this article (those related to Protocol) are outdated. (November 2013)|
|802.11 network standards|
|Data rate per stream
|Modulation||Approximate indoor range||Approximate outdoor range|
|—||Jun 1997||2.4||20||1, 2||1||DSSS, FHSS||20||66||100||330|
|a||Sep 1999||5||20||6, 9, 12, 18, 24, 36, 48, 54||1||OFDM||35||115||120||390|
|b||Sep 1999||2.4||20||1, 2, 5.5, 11||1||DSSS||35||115||140||460|
|g||Jun 2003||2.4||20||6, 9, 12, 18, 24, 36, 48, 54||1||OFDM, DSSS||38||125||140||460|
|n||Oct 2009||2.4/5||20||7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2[B]||4||OFDM||70||230||250||820|
|40||15, 30, 45, 60, 90, 120, 135, 150[B]||70||230||250||820|
|ac||Dec 2012||5||20||up to 87.6||8|
|40||up to 200|
|80||up to 433.3|
|160||up to 866.7|
|ad||~Feb 2014||2.4/5/60||up to 6912 (6.75Gb/s) |
- 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[update], it is only being licensed in the United States by the FCC.
- B1 B2 Assumes short guard interval (SGI) enabled, otherwise reduce each data rate by 10%.
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 today 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
Originally described as clause 17 of the 1999 specification, the OFDM waveform at 5.8GHz 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 54Mbit/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 5.8 GHz, 54Mbit/s (54x10^6 bits per second).
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 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.
802.11b 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.
802.11b devices 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 when compared to 802.11a by ~21%.
The then-proposed 802.11g standard was rapidly adopted by consumers 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 base standard IEEE 802.11-2007.
802.11n is an amendment which 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 lesser used 5 GHz bands. Support for 5 GHz bands is optional. It operates at a maximum net data rate 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 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 802.11-2012.
|Parts of this article (those related to 802.11ac) are outdated. (November 2013)|
IEEE 802.11ac is a standard under development which will provide throughput in the 5 GHz band. This specification will enable higher multi-station WLAN throughput of at least 1 gigabit per second and a maximum single link throughput of at least 500 megabits per second, by using wider RF bandwidth (80 or 160 MHz), more streams (up to 8), and high-density modulation (up to 256 QAM).
|Parts of this article (those related to 802.11ad) are outdated. (November 2013)|
IEEE 802.11ad "WiGig" is a published standard that is already seeing a major push from hardware manufacturers. On 24 July 2012 Marvell and Wilocity announced a new partnership to bring a new tri-band Wi-Fi solution to market. Using 60 GHz, the new standard can achieve a theoretical maximum throughput of up to 7 Gbit/s. This standard is expected to reach the market sometime in early 2014.
|This section is empty. You can help by adding to it. (November 2013)|
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 and 802.11n 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.
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 centre frequency, 802.11 also 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 only use 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 only allowed 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 through 11.
Since the spectral mask only defines 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 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." and section 184.108.40.206 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 interference seen on a 1, 5, 9, and 13 channel configuration can have very small difference from a three channel configuration and in the paper entitled "Effect of adjacent-channel interference in IEEE 802.11 WLANs" by Villegas this is also demonstrated.
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.
Most Wi-Fi certified devices default to regdomain 0, which means least common denominator settings, i.e. the device will not transmit at a power above the allowable power in any nation, nor will it use frequencies that are not permitted in any nation.
The regdomain setting is often made difficult or impossible to change so that the end users do not conflict with local regulatory agencies such as the United States' Federal Communications Commission.
Layer 2 – Datagrams
The datagrams are called "frames". Current 802.11 standards define "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 the payload. The first two bytes of the MAC header form a frame control field specifying the form and function of the frame. The frame control field is further 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 future use.
- Type: two bits identifying the type of WLAN frame. Control, Data and Management are various frame types defined in IEEE 802.11.
- Sub Type: Four bits providing additional discrimination between frames. Type and Sub type 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 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 which 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.
- WEP: The WEP bit is modified after processing a frame. It is toggled to one after a frame has been decrypted or if no encryption is set it will have already been one.
- Order: This bit is only set 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).
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.
- 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 which was added with 802.11e.
- The 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 allow for the maintenance of communication. Some common 802.11 subtypes include:
- Authentication frame: 802.11 authentication begins with the WNIC sending an authentication frame to the access point containing its identity. With an open system authentication the WNIC only sends 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 range.
- 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 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 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.
2. In terms of ICT, an Information Element (IE) is a part of management frames in the IEEE 802.11 wireless LAN protocol. IEs are a device's way to transfer descriptive information about itself inside management frames. There are usually several IEs inside each such frame, and each is built of TLVs mostly defined outside the basic IEEE 802.11 specification.
The common structure of an IE is as follows:
← 1 → ← 1 → ← 3 → ← 1-252 → ------------------------------------------------ |Type |Length| OUI | 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 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 a RTS frame to 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.
Standard and amendments
- 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 and 11 Mbit/s (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 (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 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 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)
- IEEE 802.11ad: Very High Throughput 60 GHz (December 2012) - see WiGig
- IEEE 802.11ae: Prioritization of Management Frames (March 2012)
- 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; (~ February 2014)
- IEEE 802.11af: TV Whitespace (~ June 2014)
- IEEE 802.11ah: Sub 1 GHz sensor network, smart metering. (~ January 2016)
- IEEE 802.11ai: Fast Initial Link Setup (~ February 2015)
- IEEE 802.11mc: Maintenance of the standard (~ March 2015)
- IEEE 802.11aj: China Millimeter Wave (~ October 2016)
- IEEE 802.11aq: Pre-association Discovery (~ May 2015)
- IEEE 802.11ak: General Links
To reduce confusion, no standard or task group was named 802.11l, 802.11o, 802.11q, 802.11x, 802.11ab, or 802.11ag.
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 and 802.11mb was completed for 802.11-2012.
Standard vs. amendment
Both the terms "standard" and "amendment" are used when referring to the different variants of IEEE standards.
As far as the IEEE Standards Association is concerned, there is only one current standard; it is denoted by IEEE 802.11 followed by the date that it was published. IEEE 802.11-2012 is the only version currently in publication. 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 a non-capitalized letter. For example IEEE 802.11a and IEEE 802.11b. Updating 802.11 is the responsibility of task group m. In order to create a new version, TGm combines the previous version of the standard and all published amendments. TGm also provides clarification and interpretation to industry on published documents. New versions of the IEEE 802.11 were published in 1999, 2007 and 2012.
The working title of 802.11-2007 was 802.11-REVma. This denotes a third type of document, a "revision". The complexity of combining 802.11-1999 with 8 amendments made it necessary to revise already agreed upon text. As a result, additional guidelines associated with a revision had to be followed.
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.
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 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.
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.
In December 2011, a security flaw was revealed that affects wireless routers with the optional Wi-Fi Protected Setup (WPS) feature. While WPS is not a part of 802.11, the flaw allows a remote attacker to recover the WPS PIN and, with it, the router's 802.11i password in a few hours.
Non-standard 802.11 extensions and equipment
Many companies implement wireless networking equipment with non-IEEE standard 802.11 extensions either by implementing proprietary or draft features. These changes may lead to incompatibilities between these extensions.
- Bluetooth, another wireless protocol primarily designed for shorter-range applications.
- Comparison of wireless data standards
- OFDM system comparison table
- Wi-Fi Alliance
- Wi-Fi operating system support
- Wireless Gigabit Alliance, also known as WiGig
- Fujitsu Ltd. v. Netgear Inc.
- Wireless USB, another wireless protocol primarily designed for shorter-range applications.
- IEEE 802.11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. (2012 revision). IEEE-SA. 5 April 2012. doi:10.1109/IEEESTD.2012.6178212.
- IEEE 802.11k-2008—Amendment 1: Radio Resource Measurement of Wireless LANs. IEEE-SA. 12 June 2008. doi:10.1109/IEEESTD.2008.4544755.
- IEEE 802.11r-2008—Amendment 2: Fast Basic Service Set (BSS) Transition. IEEE-SA. 15 July 2008. doi:10.1109/IEEESTD.2008.4573292.
- IEEE 802.11y-2008—Amendment 3: 3650–3700 MHz Operation in USA. IEEE-SA. 6 November 2008. doi:10.1109/IEEESTD.2008.4669928.
- "ARRLWeb: Part 97 - Amateur Radio Service". American Radio Relay League. Retrieved 2010-09-27.
- "Wi-Fi (wireless networking technology)". Encyclopædia Britannica. Retrieved 2010-02-03.
- Wolter Lemstra , Vic Hayes , John Groenewegen , The Innovation Journey of Wi-Fi: The Road To Global Success, Cambridge University Press, 2010, ISBN 0-521-19971-9
- "Wi-Fi Alliance: Organization". Official industry association web site. Retrieved August 23, 2011.
- "Official IEEE 802.11 working group project timelines". Sept. 19, 2009. Retrieved 2009-10-09.
- "Wi-Fi CERTIFIED n: Longer-Range, Faster-Throughput, Multimedia-Grade Wi-Fi® Networks" (registration required). Wi-Fi Alliance. September 2009.
- "802.11n Delivers Better Range". Wi-Fi Planet. 2007-05-31.
- "IEEE802.11ac: The Next Evolution of Wi-Fi Standards". 2012-05-11. Retrieved 2012-05-16.
- "WiGig and IEEE 802.11ad For Multi-Gigabyte-Per-Second WPAN and WLAN". Tensorcom Inc.
- Angelakis, V.; Papadakis, S.; Siris, V.A.; Traganitis, A. (March 2011). "Adjacent channel interference in 802.11a is harmful: Testbed validation of a simple quantification model". Communications Magazine (IEEE) 49 (3): 160–166. doi:10.1109/MCOM.2011.5723815. ISSN 0163-6804
- Wireless Networking in the Developing World: A practical guide to planning and building low-cost telecommunications infrastructure (2nd ed.). Hacker Friendly LLC. 2007. p. 425. page 14
- IEEE 802.11-2007
- "IEEE-SA - News & Events". Standards.ieee.org. Retrieved 2012-05-24.
- IEEE 802.11n-2009—Amendment 5: Enhancements for Higher Throughput. IEEE-SA. 29 October 2009. doi:10.1109/IEEESTD.2009.5307322.
- "Why did 802.11-2012 renumber clauses?". Matthew Gast, Aerohive Networks. Retrieved 2012-11-17.
- "Tri-Band Chip Partnership". BRIGHT SIDE OF NEWS. Retrieved 2012-07-24.
- "IEEE 802.11ad". Standards.ieee.org. Retrieved 2012-07-24.
- "Cuadro nacional de Atribución de Frecuencias CNAF". Secretaría de Estado de Telecomunicaciones. Archived from the original on 2008-02-13. Retrieved 2008-03-05.
- "Evolution du régime d’autorisation pour les RLAN". French Telecommunications Regulation Authority (ART). Retrieved 2008-10-26.
- "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications". Retrieved 2013-12-05.
- "Choosing the clearest channels for WiFi... continued". Retrieved 2013-12-05.
- "Effect of adjacent-channel interference in IEEE 802.11 WLANs". Retrieved 2013-12-05.
- "Channel Deployment Issues for 2.4 GHz 802.11 WLANs". Cisco Systems, Inc. Retrieved 2007-02-07.
- Garcia Villegas, E.; et al. (2007). "Effect of adjacent-channel interference in IEEE 802.11 WLANs". CrownCom 2007. ICST & IEEE.
- IEEE Standard 802.11-2007 page 531
- "802.11 Technical Section". Retrieved 2008-12-15.
- "Understanding 802.11 Frame Types". Retrieved 2008-12-14.
- Olivier Bonaventure. "Computer Networking : Principles, Protocols and Practice". Retrieved 2012-07-09.
- "IEEE P802.11 - TASK GROUP AC". IEEE. November 2009. Retrieved 2009-12-13.
- Fleishman, Glenn (December 7, 2009). "The future of WiFi: gigabit speeds and beyond". Ars Technica. Retrieved 2009-12-13.
- Jesse Walker, Chair (May 2009). "Status of Project IEEE 802.11 Task Group w: Protected Management Frames". Retrieved August 23, 2011.
- http://www.kb.cert.org/vuls/id/723755 US CERT Vulnerability Note VU#723755