Although the terms 802.11 and Wi-Fi are often used interchangeably, strictly speaking, this is incorrect. Wi-Fi is an industry driven interoperability certification that is based on a subset of 802.11. And in some cases, market demand has led the Wi-Fi Alliance to begin certifying products before amendments to the 802.11 standard are complete.
A Linksys Residential gateway with a 802.11b radio and a 4-port ethernet switch.
A Compaq 802.11b PCI card
The 802.11 family currently includes multiple over-the-air modulation techniques that all use the same basic protocol. The most popular techniques are those defined by the b/g and are amendments to the original standard; security was originally purposefully weak due to export requirements of multiple governments, and was later enhanced via the 802.11i amendment after governmental and legislative changes. 802.11n is a new multi-streaming modulation technique that has recently been developed; the standard is still under draft development, although products based on proprietary pre-draft versions of the standard are being sold. Other standards in the family (c–f, h, j) are service amendments and extensions or corrections to previous specifications. 802.11a was the first wireless networking standard, but 802.11b was the first widely accepted wireless networking standard, followed by 802.11g, 802.11a, and 802.11n.
802.11b and 802.11g standards use the 2.4 GHz band, operating (in the United States) under Part 15 of the FCC Rules and Regulations. Because of this choice of frequency band, 802.11b and 802.11g equipment could occasionally suffer interference from microwave ovens or cordless telephones. Bluetooth devices, while operating in the same 2.4 GHz band, do not interfere with 802.11b and 802.11g (in theory) because they use a frequency hopping spread spectrum signaling method (FHSS) while 802.11b/g uses a direct sequence spread spectrum signaling method (DSSS). The 802.11a standard uses the 5GHz band, which is reasonably free from interference by comparison and offers 23 non-overlapping channels versus the 2.4GHz three. 802.11a devices are never affected by products operating on the 2.4 GHz band.
The segment of the radio frequency spectrum used varies between countries. In the U.S. 802.11a and g devices may be legally operated without a license. Unlicensed (legal) operation of 802.11 a & g is covered under Part 15 of the FCC Rules and Regulations. Frequencies used by channels one (1) through six (6) (802.11b) fall within the range of 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 allowing any commercial content or encryption.
802.11-1997 (802.11 legacy)
The original version of the standard IEEE 802.11 released in 1997 specifies two raw data rates of 1 and 2 megabits per second (Mbit/s) to be transmitted via infrared (IR) signals or by either Frequency hopping or Direct-sequence spread spectrum in the Industrial Scientific Medical frequency band at 2.4 GHz. IR remains a part of the standard but has no actual implementations.
The original standard also defines Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) as the medium access method. A significant percentage of the available raw channel capacity is sacrificed (via the CSMA/CA mechanisms) in order to improve the reliability of data transmissions under diverse and adverse environmental conditions.
At least six different, somewhat-interoperable, commercial products appeared using the original specification, from companies like Alvarion (PRO.11 and BreezeAccess-II), BreezeCom, Digital / Cabletron (RoamAbout) , Lucent, Netwave Technologies (AirSurfer Plus and AirSurfer Pro), Symbol Technologies (Spectrum24), and Proxim (OpenAir). A weakness of this original specification was that it offered so many choices that interoperability was sometimes challenging to realize. It is really more of a "beta-specification" than a rigid specification, initially allowing individual product vendors the flexibility to differentiate their products but with little to no inter-vendor operability. Legacy 802.11 was rapidly supplemented (and popularized) by 802.11b. Widespread adoption of 802.11 networks only occurred after 802.11b was ratified and multiple product became available from multiple vendors and as a result few networks ran on the 802.11-1997 standard.
Since the 2.4 GHz band is heavily used to the point of being crowded, using the 5 GHz band gives 802.11a a significant advantage. However, this high carrier frequency also brings a slight disadvantage: The effective overall range of 802.11a is slightly less than that of 802.11b/g; 802.11a signals cannot penetrate as far as those for 802.11b because they are absorbed more readily by walls and other solid objects in their path. On the other hand, OFDM has fundamental propagation advantages when in a high multipath environment, such as an indoor office, and the higher frequencies enable the building of smaller antennas with higher RF system gain which counteract the disadvantage of a higher band of operation. The increased number of usable channels (4 to 8 times as many in FCC countries) and the near absence of other interfering systems (microwave ovens, cordless phones, baby monitors) give 802.11a significant aggregate bandwidth and reliability advantages over 802.11b/g.
Different countries have different regulatory support, although a 2003 World Radiotelecommunications Conference improved worldwide standards coordination. 802.11a is now approved by regulations in the United States and Japan, but in other areas, such as the European Union, it had to wait longer for approval. European regulators were considering the use of the European HIPERLAN standard, but in mid-2002 cleared 802.11a for use in Europe. In the U.S., a mid-2003 FCC decision may open more spectrum to 802.11a channels.
802.11a products started shipping late, lagging 802.11b products due to the slow availability of the harder to manufacture 5 GHz components needed to implement products. First generation product performance was poor and plagued with problems. When second generation products started shipping, 802.11a was not widely adopted in the consumer space primarily because the less-expensive 802.11b was already widely adopted. However, 802.11a has seen significant penetration into Enterprise network environments, despite the initial cost disadvantages for businesses which require increased capacity and reliability over 802.11b/g-only networks.
With the arrival of less expensive early 802.11g products on the market, which were backwards-compatible with 802.11b, the bandwidth advantage of the 5 GHz 802.11a in the consumer market was reduced. Manufacturers of 802.11a equipment responded to the lack of market success by significantly improving the implementations (current-generation 802.11a technology has range characteristics nearly identical to those of 802.11b), and by making technology that can use more than one band a standard.
Dual-band, or dual-mode Access Points and Network Interface Cards (NICs) that can automatically handle a and b/g, are now common in all the markets, and very close in price to b/g- only devices.
Of the 52 OFDM subcarriers, 48 are for data and 4 are pilot subcarriers with a carrier separation of 0.3125 MHz (20 MHz/64). Each of these subcarriers can be a BPSK, QPSK, 16-QAM or 64-QAM. The total bandwidth is 20 MHz with an occupied bandwidth of 16.6 MHz. Symbol duration is 4 microseconds with a guard interval of 0.8 microseconds. The actual generation and decoding of orthogonal components is done in baseband using DSP which is then upconverted to 5 GHz at the transmitter. Each of the subcarriers could be represented as a complex number. The time domain signal is generated by taking an Inverse Fast Fourier transform (IFFT). Correspondingly the receiver downconverts, samples at 20 MHz and does an FFT to retrieve the original coefficients. The advantages of using OFDM include reduced multipath effects in reception and increased spectral efficiency.
802.11b products appeared on the market in early 2000, since 802.11b is a direct extension of the DSSS (Direct-sequence spread spectrum) modulation technique defined in the original standard. Technically, the 802.11b standard uses Complementary code keying (CCK) as its modulation technique. 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 suffer interference from other products operting in the 2.4 GHz band. Devices operating in the 2.4 GHz range include: microwave ovens, Bluetooth devices, baby monitors and cordless telephones. Interference issues, and user density problems within the 2.4 GHz band have become a major concern and frustration for users.
802.11b is used in a point-to-multipoint configuration, wherein an access point communicates via an omni-directional antenna with one or more nomadic or mobile clients that are located in a coverage area around the access point. Typical indoor range is 30 m (100 ft) at 11 Mbit/s and 90 m (300 ft) at 1 Mbit/s. The overall bandwidth is dynamically demand shared across all the users on a channel. With high-gain external antennas, the protocol can also be used in fixed point-to-point arrangements, typically at ranges up to 8 kilometers (5 miles) although some report success at ranges up to 80–120 km (50–75 miles) where line of sight can be established. This is usually done in place of costly leased lines or very cumbersome microwave communications equipment. Designers of such installations who wish to remain within the law must however be careful about legal limitations on effective radiated power.
802.11b cards can operate at 11 Mbit/s, but will scale back to 5.5, then 2, then 1 Mbit/s (also known as Adaptive Rate Selection), if signal quality becomes an issue.
In June 2003, a third modulation standard was ratified: 802.11g. This works in the 2.4 GHz band (like 802.11b) but operates at a maximum raw data rate of 54 Mbit/s, or about 19 Mbit/s net throughput (identical to 802.11a core, except for some additional legacy overhead for backward compatibility). 802.11g hardware is fully backwards compatible with 802.11b hardware. Details of making b and g work well together occupied much of the lingering technical process. In an 11g network, however, the presence of a legacy 802.11b participant will significantly reduce the speed of the overall 802.11g network.
The modulation scheme used in 802.11g is orthogonal frequency-division multiplexing (OFDM) copied from 802.11a with data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbit/s, and reverts to CCK (like the 802.11b standard) for 5.5 and 11 Mbit/s and DBPSK/DQPSK+DSSS for 1 and 2 Mbit/s. Even though 802.11g operates in the same frequency band as 802.11b, it can achieve higher data rates because of its heritage to 802.11a.
The then-proposed 802.11g standard was rapidly adopted by consumers starting in January 2003, well before ratification, due to the desire for higher speeds, and 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.
Despite its major acceptance, 802.11g suffers from the same interference as 802.11b in the already crowded 2.4 GHz range. Devices operating in this range include: microwave ovens, Bluetooth devices, baby monitors and cordless telephones. Interference issues, and related problems within the 2.4 GHz band have become a major concern and frustration for users. Additionally the success of the standard has caused usage/density problems related to crowding in urban areas. This crowding can cause a dissatisfied user experience as the number of non-overlapping usable channels is only 3 in FCC nations (ch 1, 6, 11) or 4 in European nations (ch 1, 5, 9, 13). Last, the 802.11/11g MAC protocol doesn't share efficiently with more than a few users per channel relative to scaling for dense user or crowded environments. The easy solution for users who suffer density/crowding or interference problems is to deploy a seperately named (SSID) 802.11a network.
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 08, 2007, 802.11REVma was renamed to the current standard IEEE 802.11-2007. This is the single most modern 802.11 document available that contains cumulative changes from multiple sub-letter task groups.
802.11n builds upon previous 802.11 standards by adding MIMO (multiple-input multiple-output). MIMO uses multiple transmitter and receiver antennas to improve the system performance. Precoding and postcoding techniques are used at a transmitter and a receiver, respectively, to achieve the capacity of a MIMO link. Precoding includes spatial beamforming and spatial coding, where spatial beamforming improves the received signal quality at the decoding stage. Spatial coding can increase data throughput via spatial multiplexing and increase range by exploiting the spatial diversity, perhaps through such as Alamouti coding. Antennas are listed in a format of 2x2 for two receivers and two transmitters. A 4x4 is four receivers and four transmitters. The number of antennas relates to the number of simultaneous streams. The standards requirement is a 2x2 with a maximum two streams. The standard does optionally allow for the potential of a 4x4 with four streams.
The Enhanced Wireless Consortium (EWC) was formed to help accelerate the IEEE 802.11n development process and promote a technology specification for interoperability of next-generation wireless local area networking (WLAN) products.
An 802.11 access point may operate in one of three modes:
Legacy (only 802.11a, and b/g)
Mixed (802.11a, b/g, and n)
Greenfield (only 802.11n) - maximum performance
This article or section may contain a proseline.
Please help convert this timeline into prose or, if necessary, a list. (help)
Work on the 802.11n standard dates back to 2004. Publication is currently expected in September 2008, but major manufacturers are now releasing 'pre-N', 'draft n' or 'MIMO-based' products based on early specs.
January 2004 - IEEE announced that it had formed a new 802.11 Task Group (TGn) to develop a new amendment to the 802.11 standard for wireless local-area networks. The real data throughput will reach a theoretical 270 Mbit/s for the required dual stream MIMO device. (which may require an even higher raw data rate at the physical layer), and should be up to 20 times faster than 802.11b, and up to 3 times faster than 802.11a and up to 4 times faster than 802.11g.
July 2005 - Previous competitors TGn Sync, WWiSE, and a third group, MITMOT, said that they would merge their respective proposals as a draft. The standardization process is expected to be completed by the second quarter of 2009.
19 January 2006 - the IEEE 802.11n Task Group approved the Joint Proposal's specification, based on EWC's draft specification.
March 2006 - the IEEE 802.11 Working Group sent the 802.11n Draft to its first letter ballot, allowing the 500+ 802.11 voters to review the document and suggest bugfixes, changes and improvements.
2 May 2006 - the IEEE 802.11 Working Group voted not to forward Draft 1.0 of the proposed 802.11n standard. Only 46.6% voted to approve the ballot. To proceed to the next step in the IEEE standards process, a majority vote of 75% is required. This letter ballot also generated approximately 12000 comments -- much more than anticipated.
November 2006 - TGn voted to accept draft version 1.06, incorporating all accepted technical and editorial comment resolutions prior to this meeting. An additional 800 comment resolutions were approved during the November session which will be incorporated into the next revision of the draft. As of this meeting, three of the 8 comment topic ad hoc groups chartered in May have had completed their work and 88% of the technical comments had been resolved with approximately 370 remaining.
19 January 2007 - the IEEE 802.11 Working Group unanimously (100 yes, 0 no, 5 abstaining) approved a request by the 802.11n Task Group to issue a new Draft 2.0 of the proposed standard. Draft 2.0 was based on the Task Group's working draft version 1.10. Draft 2.0 was at this point in time the cumulative result of thousands of changes to the 11n document as based on all previous comments.
7 February 2007 - the results of Letter Ballot 95, a 15-day Procedural vote passed with 97.99% approval and 2.01% disapproval. On the same day, 802.11 Working Group announced the opening of Letter Ballot 97. It invited detailed technical comments to closed on 9 March 2007.
9 March 2007 - Letter Ballot 97, the 30-day Technical vote to approve Draft 2.0, closed. They were announced by IEEE 802 leadership during the Orlando Plenary on 12 March 2007. The ballot passed with an 83.4% approval, above the 75% minimum approval threshold. There were still approximately 3,076 unique comments, which will be individually examined for incorporation into the next revision of Draft 2.
22 August 2007 - Almost 70 products certified for compliance with Draft 2.0 of the 802.11n.
See also: 802.11 non-standard equipment#Pre-802.11n equipment
 Channels and international compatibility
See also: Wi-Fi Technical Information
802.11b and 802.11g – as well as 802.11n when using the 2.4 GHz band – divide the 2.4 GHz spectrum into 14 overlapping, staggered channels whose center frequencies are 5 megahertz (MHz) apart. The 802.11b, and 802.11g standards do specify the center frequency of the channel and a spectral mask width to a power level for that channel. The spectral mask for 802.11b requires that the signal be attenuated by at least 30 dB from its peak energy at ± 11 MHz from the center frequency. This means that an 802.11b/g product occupies five channels to an energy level of 30 dB down from the peak or center of the signal. For an FCC country the valid channels are one through eleven: this limits the number of non-overlapped channels to three. The normal system level channel configurations for deployments are channels 1, 6 and 11 for an FCC country and 1, 5, 9 and 13 for an European Union country.
Since the spectral mask only defines power output restrictions up to ± 22 MHz from the center frequency to be attenuated by 50 dB, 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 1, 6, and 11, the signal on any channel should be sufficiently attenuated to minimally interfere with a transmitter on any other channel. However, due to the near-far problem, a typical transmitter on an adjacent channel can impact a weaker signal on a non-overlapping channel only if it is closely placed to the victim radio (within a meter).
Although the statement that channels 1, 6, and 11 are "non-overlapping" is limited to a spacing or product density, the 1–6–11 guideline has merit. If transmitters are closer together than channels 1, 6, and 11 (for example, 1, 4, 7, and 10), overlap between the channels may cause unacceptable degradation of signal quality and throughput.
The channels that are available for use in a particular country differ according to the regulations of that country. In the United States, for example, FCC regulations only allow channels 1 through 11 to be used. In Europe channels 1–13 are licensed for 802.11b operation (with 1, 5, 9 and 13 usually deployed). In Japan, all 14 channels are licensed for 802.11b operation.
 Country Specific Licensing
In Australia there is no unlicensed spectrum, however operation of WLAN devices is allowed under the following Class Licence:
Radiocommunications Class Licence (Low Interference Potential Devices)
This licence allows for the operation of Digital modulation transmitters in the bands of 2400-2483.5 & 5725-5850 MHz bands, and the operation of Radio Local Area Network transmitters in 5150-5350 (Indoor Only), 5470-5600 & 5650-5725 MHz Bands. This corresponds to 802.11b/g channels 1 to 13, and 802.11a channels 36,40,44,48,52,56,60,64,149,153,157,161,165
 Standard and Amendments
Within the IEEE 802.11 Working Group, the following IEEE Standards Association Standard and Amendments exist:
IEEE 802.11 - THE WLAN STANDARD was original 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF and 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 & j. (July 2007)
IEEE 802.11k - Radio resource measurement enhancements (proposed - 2007?)
IEEE 802.11l - (reserved and will not be used)
IEEE 802.11m - Maintenance of the standard. Recent edits became 802.11-2007. (ongoing)
IEEE 802.11n - Higher throughput improvements using MIMO (multiple input, multiple output antennas) (September 2008)
IEEE 802.11o - (reserved and will not be used)
IEEE 802.11p - WAVE - Wireless Access for the Vehicular Environment (such as ambulances and passenger cars) (working - 2009?)
IEEE 802.11q - (reserved and will not be used, can be confused with 802.1Q VLAN trunking)
IEEE 802.11r - Fast roaming Working "Task Group r" - 2007?
IEEE 802.11s - ESS Extended Service Set Mesh Networking (working - 2008?)
IEEE 802.11T - Wireless Performance Prediction (WPP) - test methods and metrics Recommendation (working - 2008?)
IEEE 802.11u - Interworking with non-802 networks (for example, cellular) (proposal evaluation - ?)
IEEE 802.11v - Wireless network management (early proposal stages - ?)
IEEE 802.11w - Protected Management Frames (early proposal stages - 2008?)
IEEE 802.11x - (reserved and will not be used, can be confused with 802.1x Network Access Control)
IEEE 802.11y - 3650-3700 Operation in the U.S. (March 2008?)
There is no standard or task group named "802.11x". Rather, this term is used informally to denote any current or future 802.11 amendment, in cases where further precision is not necessary. (The IEEE 802.1x standard for port-based network access control is often mistakenly called "802.11x" when used in the context of wireless networks.)
802.11F and 802.11T are recommended practices, rather than standards and are capitalized as such.
 Standard or Amendment?
Both the terms "standard" and "amendment" are used when referring to the different variants of IEEE 802.11. Which is correct?
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 802.11-2007 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 and 2007.
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 IEEE 802.1D bridge. A Portal provides access to the WLAN by non-802.11 LAN STAs.
 Community networks
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 high speed Internet connection.
Many hotspot or free networks frequently allow anyone within range, including a 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 entitled "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 government strength encryption in 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 PreShared Key) and for the Enterprise space is WPA2 along with a radius server the strongest is EAP-TLS.
In January 2005, IEEE set up yet another task group TGw to protect management and broadcast frames, which previously were sent unsecured. See IEEE 802.11w
 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.
For more details on this topic, see 802.11 non-standard equipment.
 See also
AirPort, Apple wireless system based on 802.11 (b, g, and n).
Bluetooth, another wireless protocol primarily designed for shorter range applications.
WiMAX (also known as 802.16), another wireless protocol designed for MANs.
Spectral efficiency comparison table
List of device bandwidths
 External links
IEEE 802.11 working group
Download the 802.11 standards from IEEE
Official IEEE 802.11 Work Plan predictions
"Using the Fluhrer, Mantin, and Shamir Attack to Break WEP" (2001), paper by Stubblefield (PDF)
^ ARRLWeb: Part 97 - Amateur Radio Service. American Radio Relay League.
^ IEEE 802.11 Working Group (2007-06-12). IEEE 802.11-2007: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. ISBN 0-7381-5656-9.
^ http://www.enhancedwirelessconsortium.org/ Enhanced Wireless Consortium
^ a b Official IEEE 802.11 working group project timelines (2007-07-02). Retrieved on 2007-07-09.
^ Channel Deployment Issues for 2.4 GHz 802.11 WLANs. Cisco Systems, Inc. Retrieved on 2007-02-07.
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