802.11 is a set of IEEE standards that govern wireless networking transmission methods. They are commonly used today in their 802.11a, 802.11b, 802.11g, 802.11n and 802.11ac versions to provide wireless connectivity in the home, office and some commercial establishments.
802.11b has a maximum raw data rate of 11 Mbit/s and uses the same CSMA/CA media access method defined in the original standard. Due to the CSMA/CA protocol overhead, in practice the maximum 802.11b throughput that an application can achieve is about 5.9 Mbit/s using TCP and 7.1 Mbit/s using UDP.
802.11b products appeared on the market in mid-1999, since 802.11b is a direct extension of the DSSS (Direct-sequence spread spectrum) modulation technique defined in the original standard. The Apple iBook was the first mainstream computer sold with optional 802.11b networking. 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 operating 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 omnidirectional antenna with mobile clients within the range of the access point. Typical range depends on the radio frequency environment, output power and sensitivity of the receiver. Allowable bandwidth is shared across clients in discrete channels. A directional antenna focuses output power into a smaller field which increases point-to-point range. Designers of such installations who wish to remain within the law must however be careful about legal limitations on effective radiated power.
Some 802.11b cards operate at 11 Mbit/s, but scale back to 5.5, then to 2, then to 1 Mbit/s (also known as Adaptive Rate Selection) in order to decrease the rate of re-broadcasts that result from errors.
Channels and Frequencies
802.11b/g channels in 2.4 GHz band
802.11b channel to frequency map
|Channel||Center Frequency||Frequency delta||Channel Width||Overlaps Channels|
|1||2.412 GHz||5 MHz||2.401–2.423 GHz||2-5|
|2||2.417 GHz||5 MHz||2.406–2.428 GHz||1,3-6|
|3||2.422 GHz||5 MHz||2.411–2.433 GHz||1-2,4-7|
|4||2.427 GHz||5 MHz||2.416–2.438 GHz||1-3,5-8|
|5||2.432 GHz||5 MHz||2.421–2.443 GHz||1-4,6-9|
|6||2.437 GHz||5 MHz||2.426–2.448 GHz||2-5,7-10|
|7||2.442 GHz||5 MHz||2.431–2.453 GHz||3-6,8-11|
|8||2.447 GHz||5 MHz||2.436–2.458 GHz||4-7,9-12|
|9||2.452 GHz||5 MHz||2.441–2.463 GHz||5-8,10-13|
|10||2.457 GHz||5 MHz||2.446–2.468 GHz||6-9,11-13|
|11||2.462 GHz||5 MHz||2.451–2.473 GHz||7-10,12-13|
|12||2.467 GHz||5 MHz||2.456–2.478 GHz||8-11,13-14|
|13||2.472 GHz||5 MHz||2.461–2.483 GHz||9-12, 14|
|14||2.484 GHz||12 MHz||2.473–2.495 GHz||12-13|
Note: Channel 14 is only allowed in Japan, Channels 12 & 13 are allowed in most parts of the world, except the USA, where only Channels 1 to 11 are legal to use. More information can be found in the List of WLAN channels.