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IEEE 802.11 wireless standards

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Computer Studies wireless router

The Institute of electrical and electronic engineers IEEE 802.11 wireless standards, the original 802.11 standards were released in 1997 and operated at 2.4 GHz and offered data transfer rates of 1 - 2 Mbps this standard used DSSS or Direct sequence spread spectrum and FHSS or Frequency hopping spread spectrum signalling, this was replaced by the 802.11a standard in 1999 this used the 5.0 GHz frequency and had data transfer rates of up to 54 Mbps and used OFDM or Orthogonal frequency division multiplexing signalling, and because of the frequency range was resistant to interference from cell phones, microwaves etc, it had a range of 30 - 50 meters.

Around the same time the 802.11b standard was released this was not compatible with 802.11a, data transfer rates of 11 Mbps and it used the 2.4 GHz frequency, it was approved by the Wi-Fi alliance and introduced WEP or Wired equivalent privacy encryption, this standard used DSSS or Direct sequence spread spectrum signalling and offers a range of up to 100 meters, the 802.11g standard released in 2003 was interoperable with 802.11b, and operates in the 2.4 GHz frequency range with data transfer speeds of up to 54 Mbps with a range of up to 50 meters, and uses OFDM or Orthogonal frequency division multiplexing signalling, it is subject to interference from cell phones, microwaves etc because of the frequency range, the latest standard 802.11n it is interoperable with the 802.11b and 802.11g standards and should operate in both the 2.4 and 5.0 GHz frequency with data transfer speeds between 200 - 600 Mbps and a range of 50 - 600 meters.

The 802.11i security standard introduced in 2004 specifies security standards for wireless networks implemented by WPA2 or Wi-Fi protected access 2 a replacement for the WEP encryption and further improvements on WPA encryption standard which was introduced to solve weaknesses in WEP encryption, the WEP encryption standard which is known to be vulnerable to attack from hackers with weaknesses of a small IV or initialisation vector (24 bits), repetition of keys, weak encryption algorithm (RC4), for more on RC4 wikipedia.org, WPA2 has AES block cipher used to encrypt keys and a (48 bit) IV or initialisation vector, it can also use 802.1X for authentication and key distribution, 802.11i is supported by most operating systems Windows XP SP2, Vista, Linux and some Macintosh computers, some equipment might need firmware updates to support WPA2.

Some other 802.11 standards for wireless implementations include 802.11e addresses QOS or Quality of service which deals with VOIP voice over IP and media streaming, 802.11f addresses roaming and multi vendor interoperability making sure devices by different manufacturers work together, 802.11h European use of the 5.0 GHz bandwidth, 802.15.1 Bluetooth standard, Wireless access protocol version 1 and version 2 which standardises web sites for use with mobile devices, 802.1X cover port-based authentication and encryption for wireless devices and networks. For more on the IEEE802.11 standards wikipedia.org

Wireless signals travel as energy usually in waves, the frequency is the number of waves in a given time period usually measured in Hertz cycles per second, common measurements are MHz and GHz and common frequencies are 2.4 and 5.0 GHz, amplitude the height of the each wave gain/loss is the increase/decrease of amplitude measured in decibels, wireless networking operates in the SHF or super high frequency range of 3 - 30 GHz, waves have certain characteristics, reflection happens when a radio wave bounces off an object, refraction is when the radio wave passes through an object but leaves at a different angle, diffraction is when a radio wave passes around an object, scattering is when a radio wave breaks up in to multiple signals out of phase with the original signal, amplification is when the signal is boosted, attenuation reduces signal activity, a multi-path signal is when the radio wave is reflected or refracted and has broken up and out of phase from the original signal, radio frequency interference can be electrical noise or interference from weather or other devices.

The Institute of electrical and electronic engineers ieee.org

Radio waves require power

RF power is expressed in Watts

1 Watt (W) = 1 amp of current at 1 Volt, basic RF power measurements can be from milliwatts (mW) to thousands of Watts, wireless technologies are usually expressed in milliwatts (mW) Gain: is increased amplitude resulting from increasing power by optimal antenna use. Loss is a decrease in amplitude by decreasing power these are measured in decibels (dB) based on absolute power, decibels correlate to Watts uses factors of 3 and 10 to convert

1 mW = 0 dB, 10 mW = 10 dB, 1 W = 30 dB

dBm decibels with reference to milliwatts the relationship between decibels and Watts is logarithmic the formula is P (dBm) = 10* (log(P(mw))) a shortcut method uses 3 and 10 to calculate.

The range of a RF signal depends on several factors, power, frequency and interference with an increase in power there's an increase in range a decrease in power a decrease in range, frequency effects range the higher the frequency the shorter the waves and the lower the frequency the longer the waves and under the same amount of power lower frequencies travel father 802.11b/g have a greater range than 802.11a, interference can limit range, electrical noise, weather other transmission can limit the range to combat interference you can use RF shielding, more power, move devices that are creating interference. The speeds of wireless networks are measured in bits per second, with older modems connections where measured in Kbps (14.4, 36.6 and 54 Kbps) and modern LAN speeds are 10/100 and 1000 Mbps (Gigabit Ethernet)

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