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Chapter 3 - Reference
5. Glossary
Access Point (AP)
An networking device that seamlessly connects wired and wireless networks. Access
Points combined with a distributed system support the creation of multiple radio cells
that enable roaming throughout a facility.
Ad Hoc
A wireless network composed solely of stations within mutual communication range
of each other (no Access Point).
Basic Service Area (BSS)
A set of stations controlled by a single coordination function.
Broadband
A type of data transmission in which a single medium (such as cable) carries
several channels of data at once.
Channel
An instance of medium use for the purpose of passing protocol data units that may be
used simultaneously, in the same volume of space, with other instances of medium use
(on other channels) by other instances of the same physical layer, with an acceptably
low frame error ratio due to mutual interference.
Client
A client is the desktop or mobile PC that is connected to your network.
COFDM (for 802.11a or 802.11g)
Signal power alone is not enough to maintain 802.11b-like distances in an 802.11a/g
environment. To compensate, a new physical-layer encoding technology was designed
that departs from the traditional direct-sequence technology being deployed today. This
technology is called COFDM (coded OFDM). COFDM was developed specifically
for indoor wireless use and offers performance much superior to that of spread-spectrum
solutions. COFDM works by breaking one high-speed data carrier into several lower-
speed subcarriers, which are then transmitted in parallel. Each high-speed carrier is 20
MHz wide and is broken up into 52 subchannels, each approximately 300 KHz wide.
COFDM uses 48 of these subchannels for data, while the remaining four are used for
error correction. COFDM delivers higher data rates and a high degree of multipath
reflection recovery, thanks to its encoding scheme and error correction.
Each subchannel in the COFDM implementation is about 300 KHz wide. At the low
end of the speed gradient, BPSK (binary phase shift keying) is used to encode 125
Kbps of data per channel, resulting in a 6,000-Kbps, or 6 Mbps, data rate. Using
quadrature phase shift keying, you can double the amount of data encoded to 250 Kbps
48
ASUS WLAN Card
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