IEEE 802.11 or Wi-Fi

IEEE 802.11 or Wi-Fi denotes a set of Wireless LAN standards developed by
working group 11 of IEEE 802.

The 802.11 family currently includes three separate protocols that focus on
encoding; other standards in the family 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.

Protocols

802.11a

In 2001, a faster relative started shipping, 802.11a, 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 Mbps, and more realistic speeds in the mid-20
Mbps. 802.11a has not yet seen wide adoption because of the high adoption
rate of 802.11b, and concerns about range: at 5 GHz, 802.11a cannot reach as
far with the same power limitations, and may be absorbed more readily. Most
manufacturers of 802.11a equipment countered the lack of market success by
releasing dual-band/dual-mode or tri-mode cards that can automatically
handle 802.11a and b or a/b/g as available, or access points which can
support all standards simultaneously. 802.11a has 12 nonoverlapping
channels, 8 dedicated to indoor and 4 to point to point. Different countries
have different ideas about support, although a 2003 World
Radiotelecommunciations Conference made it easier for use worldwide. A
mid-2003 FCC decision may open more spectrum to 802.11a channels as well.

802.11b

802.11b has a range of about 150 feet (50 meters) with the low-gain
omnidirectional antennas typically used in 802.11b devices. 802.11b has a
maximum throughput of 11 Megabits per second (Mbps), however a significant
percentage of this bandwidth is used for communications overhead; in
practice the maximum throughput is about 5.5 Mbps. Metal, water, and
particularly thick walls absorb 802.11b signals and decrease the range
drastically. 802.11 runs in the 2.4 GHz spectrum and uses Carrier Sense
Multiple Access with Collision Avoidance (CSMA/CA) as its media access
method.

With high-gain external antennas, the protocol can also be used in fixed
point-to-point scenarios (5 miles/8 kilometres), reports of up to 50-75
miles (80-120 kilometres) line of sight) to replace costly leased lines, or
in place of very cumbersome microwave communications gear. Current cards can
operate at 11 Mbps, but will scale back to 5.5, then 2, then 1, if signal
strength is an issue. 802.11b divides spectrum in 14 overlapping, staggered
channels of 22 megahertz (MHz) each. Different channels or ranges are legal
in different countries. Three or four channels may be used simultaneously in
the same area with little or no overlap, typically 1, 6, and 11.

802.11g

In June 2003, a third standard for encoding was ratified: 802.11g. This
flavor works in the 2.4 GHz band, but operates at 54 Mbps raw or about 22
Mbps net throughput. It is fully backwards compatible with b, and details of
making b and g work together well occupied much of the lingering technical
process. 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.

Certification

Because the IEEE only sets specifications but doesn't test 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, guarantees
interoperability. Currently, Wi-Fi can mean any of 802.11a, b, or g; by
fall, Wi-Fi also includes the security standard Wi-Fi Protected Access or
WPA. Products that say Wi-Fi are supposed to also indicate the band in which
they operate in, 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 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)
   * IEEE 802.11h - 5 GHz spectrum and transmit power management for
     European compatibility
   * IEEE 802.11i - Enhanced security
   * IEEE 802.11j - Extensions for Japan
   * IEEE 802.11n - higher throughput improvements

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 not protected and let "people on the street" 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 an
paper describing a weakness in 802.11b described by Fluhrer, Mantin, and
Shamir entitled "Weaknesses in the Key Scheduling Algorithm of RC4". This
presentation was soon followed by 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). While 802.11i is still a work in
progress, and is not expected to be completed until late 2003, the Wi-Fi
Alliance has 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, and implementation will be mandatory by fall
2003 in order to display the Wi-Fi logo.

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