Tuesday, January 15, 2008

Introduction to WiFi Standards

Introduction to WiFi Standards

IEEE created the first WLAN standard in 1997. They called it 802.11. 802.11 works in radio signaling frequency - 2.4 GHz and only supported a maximum bandwidth of 2 Mbps - too slow for most applications. For this reason, ordinary 802.11 wireless products are no longer being manufactured


a) 802.11b

IEEE expanded on the original 802.11 standard in July 1999, creating the 802.11b specification. 802.11b supports bandwidth up to 11 Mbps, comparable to Ethernet.

802.11b also uses the same radio signaling frequency - 2.4 GHz - as 802.11 standard. Being an unregulated frequency, 802.11b gear can incur interference from microwave ovens, cordless phones, and other appliances using the same 2.4 GHz range. However, by installing 802.11b box a reasonable distance from other appliances, interference can easily be avoided.

Operating Frequency: 2.4GHz ISM
Transfer Rate (theoretical): 1, 2, 5.5, 11Mbps
Transfer Rate (throughput): 4Mbps (average)
Mechanism: Direct Sequence Spread Spectrum (DSSS)
Channels Available: 11 (3 non-overlapping)
Maximum Range: 175ft. (average)

-Advantages of 802.11b - lowest cost; signal range is best and is not easily obstructed
-Disadvantages of 802.11b - slowest maximum speed; supports fewer simultaneous users; appliances may interfere on the unregulated frequency band

cool.gif 802.11a
When 802.11b was developed, IEEE created a second extension to the original 802.11 standard called 802.11a. Because 802.11b gained in popularity much faster than did 802.11a, some folks believe that 802.11a was created after 802.11b. In fact, 802.11a was created at the same time. Due to its higher cost, 802.11a fits predominately in the business market, whereas 802.11b better serves the home market.

802.11a supports bandwidth up to 54 Mbps and signals in a regulated 5 GHz range. Compared to 802.11b, this higher frequency limits the range of 802.11a. The higher frequency also means 802.11a signals have more difficulty penetrating walls and other obstructions. Because 802.11a and 802.11b utilize different frequencies, the two technologies are incompatible with each other. Some vendors offer hybrid 802.11a/b network gear, but these products simply implement the two standards side by side.
Operating Frequency: 5.8 GHz Unlicensed National Information Infrastructure (UNII)

Transfer Rate (theoretical): up to 54Mbps
Transfer Rate (throughput): 20 - 36 (approximate average)
Mechanism: Orthogonal Frequency Division Multiplexing (OFDM)
Channels Available: 12 (all non-overlapping)
Maximum Range: 80ft. (average)

-Advantages of 802.11a - fastest maximum speed; supports more simultaneous users; regulated frequencies prevent signal interference from other devices
-Disadvantages of 802.11a - highest cost; shorter range signal that is more easily obstructed

c) 802.11g
In 2002 and 2003, WLAN products supporting a new standard called 802.11g began to appear on the scene. 802.11g attempts to combine the best of both 802.11a and 802.11g. 802.11g supports bandwidth up to 54 Mbps, and it uses the 2.4 GHz frequency for greater range. 802.11g is backwards compatible with 802.11b, meaning that 802.11g access points will work with 802.11b wireless network adapters and vice versa.

Operating Frequency: 2.4 GHz
Transfer Rate (theoretical): 54Mbps
Transfer Rate (throughput): 20 - 30 (average)
Mechanism: Complimentary Code Keying (CCK), OFDM
Channels: 3 (1, 6, 11)
Maximum Range: 175ft (average)

-Advantages of 802.11g - fastest maximum speed; supports more simultaneous users; signal range is best and is not easily obstructed
-Disadvantages of 802.11g - costs more than 802.11b; appliances may interfere on the unregulated signal frequency


While the major players in the world or wireless networking are the IEEE standards 802.11a, 802.11b and currently 802.11g, there are various other standard task and working groups involved with numerous components or wireless networking. Such standard development helps to improve the transmission of its data and promote the effective communication between its systems. The following are current standards and task groups which work to continually enhance and expand the functionality of the overall 802.11 protocol.

802.11c: Bridging the Gap
This standard is responsible for helping to ensure effective bridged connections between access points. Companies and universities often utilized this standard when attempting to span their networks across various environments such as building and other wide-spread installations requiring bridged communication

802.11d: Global Harmony
After its initial inception, 802.11 had very little to worry about in regards to stepping on the proverbial electronic feet of others. The introduction of the 802.11d standard task group has its sights set on making the widespread proliferation and adoption of 802.11 a globally pleasant experience. 802.11d is an ongoing standard group which seeks to further enhance as well as define new PHY requirements that comply with regulatory standards existent within other countries. This standard is of particular importance for groups which utilize the 5 GHz band as the use of the frequency differs dramatically
from country to country.

802.11f: Roaming Around
The main function of the 802.11f standards work group is to help resolve the issue of inter-compatibility between access points from different vendors. The 802.11 protocol was initially designed without such specific constraints as to allow for maximum flexibility when working with different systems. However, the rapid proliferation of diverse wireless networking technology from numerous vendors has spawned the need for an established standard allowing users to maximize their mobility. The focus of the 802.11f working group is to help promote WiFi allowing for enhanced compatibility between various wireless vendors and their products.

802.11i: Security
After WEP encryption was effectively surpassed in August 2001, the 802.11i work group began to receive more attention, specifically since its main focus is enhanced wireless security. 802.11i is a two layer standard group which focuses both on issues concerning 802.1X (not a part of the 802.11 standard) and network security, as well as a deeper look into a specific WEP security fix called Temporal Key Integrity (TKI).

802.11e: Quality Control
802.11e is a standard of increasing importance as the utilization of wireless transmission of voice and video continues to expand on a daily basis. Since its inception the 802.11 standard has lacked any mechanism for the prioritization and organization of wireless network traffic. The focus of the 802.11e standard work group is to promote and improve Quality of Service for both audio and video across the entire 802.11 standard. Its implementation will allow for backwards compatibility with existing wireless LAN's and should help to drastically improve the transfer and presentation of such data.

source :http://www.governmentsecurity.org/archive/t11352.html

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