Table of Contents
Advertisement
Chapter 5 - Glossary
systems of the same type.
IEEE 802.11
IEEE 802.xx is a set of specifications for LANs from the Institute of Electrical and
Electronic Engineers (IEEE). Most wired networks conform to 802.3, the specification
for CSMA/CD based Ethernet networks or 802.5, the specification for token ring
networks. 802.11 defines the standard for wireless LANs encompassing three
incompatible (non-interoperable) technologies: Frequency Hopping Spread Spectrum
(FHSS), Direct Sequence Spread Spectrum (DSSS), and Infrared. 802.11 specifies a
carrier sense media access control and physical layer specifications for 1 and 2 Mbps
wireless LANs.
IEEE 802.11a (54Mbits/sec)
Compared with 802.11b: The 802.11b standard was designed to operate in the 2.4-
GHz ISM (Industrial, Scientific and Medical) band using direct-sequence spread-
spectrum technology. The 802.11a standard, on the other hand, was designed to operate
in the more recently allocated 5-GHz UNII (Unlicensed National Information
Infrastructure) band. And unlike 802.11b, the 802.11a standard departs from the
traditional spread-spectrum technology, instead using a frequency division multiplexing
scheme that's intended to be friendlier to office environments.
The 802.11a standard, which supports data rates of up to 54 Mbps, is the Fast Ethernet
analog to 802.11b, which supports data rates of up to 11 Mbps. Like Ethernet and Fast
Ethernet, 802.11b and 802.11a use an identical MAC (Media Access Control). However,
while Fast Ethernet uses the same physical-layer encoding scheme as Ethernet (only
faster), 802.11a uses an entirely different encoding scheme, called OFDM (orthogonal
frequency division multiplexing).
The 802.11b spectrum is plagued by saturation from wireless phones, microwave ovens
and other emerging wireless technologies, such as Bluetooth. In contrast, 802.11a
spectrum is relatively free of interference.
The 802.11a standard gains some of its performance from the higher frequencies at
which it operates. The laws of information theory tie frequency, radiated power and
distance together in an inverse relationship. Thus, moving up to the 5-GHz spectrum
from 2.4 GHz will lead to shorter distances, given the same radiated power and encoding
scheme.
ASUS WLAN Card
63
Advertisement
Table of Contents
