IEEE 802.11

IEEE 802.11 or Wi-Fi denotes a set of Wireless LAN standards developed by working group 11 of IEEE 802. The term is also used specifically for the original version; to avoid confusion that is sometimes called "802.11legacy".

The 802.11 family currently includes three separate protocols that focus on encoding (a, b, g); security was originally included, but is now part of other family standards (e.g., 802.11i). Other standards in the family (c–f, h–j, n) are service enhancement and extensions, or corrections to previous specifications. 802.11b was the first widely accepted wireless networking standard, followed, paradoxically, by 802.11a and 802.11g.

802.11b and 802.11g standards use the unlicensed 2.4 GHz band. The 802.11a standard uses the 5 GHz band. Operating in an unregulated frequency band, 802.11b and 802.11g gears can incur interference from microwave ovens, cordless phones, and other appliances using the same 2.4 GHz range.

Protocols

802.11legacy

The original version of the standard IEEE 802.11 released in 1997 and sometimes called "802.1y" specifies two data rates of 1 and 2 Megabits per second (Mbit/s) to be transmitted via infrared (IR) signals or in the Industrial Scientific Medical frequency band at 2.4 GHz. IR has been dropped from later revisions of the standard, because it couldn't succeed against the well established IrDA protocol and has had no actual implementations. Legacy 802.11 was rapidly succeeded by 802.11b. At least five different, non-interoperable, commercial products appeared using this specification, from companies like Alvarion (PRO.11 and BreezeAccess-II) and Proxim (OpenAir and RangeLAN). A weakness of this original specification was that it offered so many choices that interoperability could not ever be realized. It is really more of a "meta-specification" than a rigid specification.

802.11b

802.11b has a raw throughput of 11 Mbit/s and uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) as its media access method. A significant percentage of the available channel capacity is wasted because of the CSMA/CA. In practice the maximum throughput that an application can achieve is about 5.5 Mbit/s. Metal, water, and thick walls absorb 802.11b signals and decrease the range drastically. 802.11 runs in the 2.4 GHz spectrum.

With high-gain external antennas, the protocol can also be used in fixed point-to-point arrangements, typically at ranges up to eight kilometers (although some report success at ranges up to 80–120 km where line of sight can be established). This is usually done to replace costly leased lines, or in place of very cumbersome microwave communications equipment. Current cards can operate at 11 Mbit/s, but will scale back to 5.5, then 2, then 1, if signal strength becomes an issue.

Extensions have been made to the 802.11b protocol (e.g., channel bonding and burst transmission techniques) in order to increase speed to 22, 33, and 44 Mbit/s, but the extensions are proprietary and have not been endorsed by the IEEE. Many companies call enhanced versions "802.11b+".

The first widespread commercial use of the 802.11b standard for networking was made by Apple Computer under the trademark AirPort. On the non-Apple market, Linksys could be considered the current leader.

Channels and international compatibility

802.11b and 802.11g divide the spectrum into 14 overlapping, staggered channels of 22 megahertz (MHz) each. Channels 1, 6, 11 and 14 do not overlap and those channels (or other sets with similar gaps) can be used such that multiple networks can operate in a close proximity without interfering with each other.

Channels 10 and 11 are the only channels which work in all parts of the world, because Spain hasn't licensed channels 1 to 9 for 802.11b operation. The full frequency list from IEEE STD 802.11b-1999/Cor 1-2001 is:

802.11a

In 2001, 802.11a, a faster related protocol started shipping even though the standard was ratified in 1999. The 802.11a standard uses the 5 GHz band, and operates at a raw speed of 54 Mbit/s, and more realistic net achievable speeds in the mid-20 Mbit/s. The speed is reduced to 48, 36, 34, 18, 12, 9 then 6 Mbit/s if required. 802.11a has 12 non-overlapping channels, 8 dedicated to indoor and 4 to point to point. Different countries have different ideas about regulatory support, although a 2003 World Radiotelecommunciations Conference made it easier for use worldwide. A mid-2003FCC decision may open more spectrum to 802.11a channels as well.

802.11a has not seen wide adoption because of the high adoption rate of 802.11b, and because of concerns about range: at 5 GHz, 802.11a cannot reach as far as 802.11b, other things (such as same power limitations) being equal; it is also absorbed more readily. Most manufacturers of 802.11a equipment countered the lack of market success by releasing dual-band or dual-mode/tri-mode cards that can automatically handle 802.11a and b or a, b and g as available. Access point equipment which can support all these standards simultaneously is also available.

802.11g

In June 2003, a third standard for encoding was ratified: 802.11g. This flavor works in the 2.4 GHz band (like 802.11b) but operates at 54 Mbit/s raw, or about 24.7 Mbit/s net, throughput like 802.11a. It is fully backwards compatible with b and uses the same frequencies. Details of making b and g work together well occupied much of the lingering technical process. In older equipment, however, the presence of an 802.11b participant significantly reduces the speed of an 802.11g network.

The 802.11g standard swept the consumer world of early adopters starting in January 2003, well before ratification. The corporate users held back and Cisco and other big equipment makers waited until ratification. By summer 2003, announcements were flourishing. Most of the dual-band 802.11a/b products became dual-band/tri-mode, supporting a, b, and g in a single card or access point.

A new feature called Super G is now integrated in certain access points. These can boost network speeds up to 108 Mbit/s by using channel bonding. This feature may interfere with other networks and may not support all b and g client cards. In addition, packet bursting techniques are also available in some chipsets and products which will also considerably increase speeds. Again, they may not be compatible with some equipment.

The first major manufacturer to use 802.11g was Apple, under the trademark AirPort Extreme. Cisco joined the game by buying up Linksys, an early adopter, and also offers its own wireless clients under the name Aironet.

802.11n

In January 2004 IEEE announced that it will develop a new standard for wide-area wireless networks. The real speed would be 100 Mbit/s (even 250 Mbit/s in PHY level), and so up to 4–5 times faster than 802.11g, and perhaps 50 times faster than 802.11b. As projected, 802.11n will also offer a better operating distance than current networks. The standardization progress is expected to be completed by the end of 2006.

802.11n builds upon previous 802.11 standards by adding MIMO (multiple-input multiple-output). The additional transmitter and receiver antennas allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity through coding schemes like Alamouti coding.

Overview

To be merged:

• IEEE 802.11a, which operates around the 5 GHz band, enjoys relatively clear-channel operation in the United States and Japan. In other areas, such as the EU, 802.11a had a longer wait for approval, and European regulators were considering the use of the European HIPERLAN standard. 802.11a was cleared for use in Europe around mid 2002. 802.11a also provides for up to 54 Mbit/s operation, but is not interoperable with 802.11b, except in the case of equipment implementing both standards.

Certification

Because the IEEE only sets specifications but does not test equipment for compliance with them, a trade group called the Wi-Fi Alliance runs a certification program that members pay to participate in. Virtually all companies selling 802.11 equipment are members. The Wi-Fi trademark, owned by the group and usable only on compliant equipment, is intended to guarantee interoperability. Currently, "Wi-Fi" can mean any of 802.11a, b, or g. As of fall 2003, Wi-Fi also includes the security standard Wi-Fi Protected Access or WPA. Eventually "Wi-Fi" will also mean equipment which implements the 802.11i security standard (aka WPA2). Products that say they are Wi-Fi are supposed to also indicate the frequency band in which they operate, 2.4 or 5 GHz.

Standards

The following standards and task groups exist with the working group:

• IEEE 802.11 - The original 2 Mbit/s, 2.4 GHz standard
• 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 802.11d - New countries
• IEEE 802.11e - Enhancements: QoS, including packet bursting
• IEEE 802.11f - Inter-Access Point Protocol (IAPP)
• IEEE 802.11g - 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003)
• IEEE 802.11h - 5 GHz spectrum, Dynamic Channel/Frequency Selection (DCS/DFS) and Transmit Power Control (TPC) for European compatibility
• IEEE 802.11i (ratified 24 June 2004) - Enhanced security
• IEEE 802.11j - Extensions for Japan
• IEEE 802.11n - Higher throughput improvements
• IEEE 802.11p - Adding wireless capabilities to mobile vehicles such as ambulances and passenger cars

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.

Wireless office networks are often unsecured or secured with WEP, which is easily broken. These networks frequently allow "people on the street" 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.

Security

In 2001, a group from the University of California at Berkeley presented a paper describing weaknesses in 802.11; 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 announcing 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 Wireless Protected Access (WPA) based on a subset of the current IEEE draft. These started to appear in products in mid-2003. 802.11i (aka WPA2) itself was ratified in June 2004, and uses the Advanced Encryption Standard, instead of RC4, which was used in WEP and WPA.

See also

• Bluetooth, another wireless protocol primarily designed for shorter range applications.
• Apple Airport, with implementations of 802.11b and 802.11g.
• Linksys, current market-leader in 802.11b and 802.11g on the Wintel platform.
• Wimax (aka 802.16), another wireless protocol designed for MANs.

External links

• the working group's own website, http://www.ieee802.org/11/
• where to download the 802.11 protocol reference: http://standards.ieee.org/getieee802/802.11.html
• Wi-Fi Alliance website, http://www.wi-fi.org/
• "Weaknesses in the Key Scheduling Algorithm of RC4", Scott Fluhrer, Itsik Mantin, Adi Shamir, http://citeseer.nj.nec.com/fluhrer01weaknesses.html
• Attack verification by Stubblefield, (original gone, wep_attack paper mirrored here) http://ftp.die.net/mirror/papers/802.11/
• Wireless LAN Security whitepapers & howto's (http://802.11-security.com/security/links)
• WLAN in Debian (http://wiki.debian.net/index.cgi?Wi-fi).
• Software-based positioning system for standard IEEE 802.11 networks, Ekahau (http://www.ekahau.com)

"HostAP" Software Access Point [Implementation of IEEE 802.11] on Linux Systems.

You can convert Any Prism 2/2.5/3.0 chipset based Wireless Access Card to function as Access Point using "HostAP" implementation [1] (http://hostap.epitest.fi/) (note: Atheros and PrismGT cards can also work as 802.11g Access Points using the madwifi and prism54 drivers respectively).

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