WL230USB-L
54Mbps Wireless 802.11b/g USB 2.0
Adaptor
- 17 -
Appendix A: Glossary
802.11b
-
The 802.11b standard specifies a wireless networking at 11 Mbps using
direct-sequence spread-spectrum (DSSS) technology and operating in the unlicensed radio
spectrum at 2.4GHz, and WEP encryption for security. 802.11b networks are also referred to as
Wi-Fi networks.
802.11g
-
specification for wireless networking at 54 Mbps using direct-sequence
spread-spectrum (DSSS) technology, using OFDM modulation and operating in the unlicensed
radio spectrum at 2.4GHz, and backward compatibility with IEEE 802.11b devices, and WEP
encryption for security.
Ad-hoc Network -
An ad-hoc network is a group of computers, each with a wireless Adaptor,
connected as an independent 802.11 wireless LAN. Ad-hoc wireless computers operate on a
peer-to-peer basis, communicating directly with each other without the use of an access point.
Ad-hoc mode is also referred to as an Independent Basic Service Set (IBSS) or as peer-to-peer
mode, and is useful at a departmental scale or SOHO operation.
DSSS
(
D
irect-
S
equence
S
pread
S
pectrum)
-
DSSS generates a redundant bit pattern for all data
transmitted. This bit pattern is called a chip (or chipping code). Even if one or more bits in the chip
are damaged during transmission, statistical techniques embedded in the receiver can recover
the original data without the need for retransmission. To an unintended receiver, DSSS appears
as low power wideband noise and is rejected (ignored) by most narrowband receivers. However,
to an intended receiver (i.e. another wireless LAN endpoint), the DSSS signal is recognized as the
only valid signal, and interference is inherently rejected (ignored).
FHSS
(
F
requency
H
opping
S
pread
S
pectrum)
-
FHSS continuously changes (hops) the carrier
frequency of a conventional carrier several times per second according to a pseudo-random set of
channels. Because a fixed frequency is not used, and only the transmitter and receiver know the
hop patterns, interception of FHSS is extremely difficult.
Infrastructure Network -
An infrastructure network is a group of computers or other devices,
each with a wireless Adaptor, connected as an 802.11 wireless LAN. In infrastructure mode, the
wireless devices communicate with each other and to a wired network by first going through an
access point. An infrastructure wireless network connected to a wired network is referred to as a
Basic Service Set (BSS). A set of two or more BSS in a single network is referred to as an
Extended Service Set (ESS). Infrastructure mode is useful at a corporation scale, or when it is
necessary to connect the wired and wireless networks.
Spread Spectrum -
Spread Spectrum technology is a wideband radio frequency technique
developed by the military for use in reliable, secure, mission-critical communications systems. It is
designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words,
more bandwidth is consumed than in the case of narrowband transmission, but the trade off
produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver
knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to
the right frequency, a spread-spectrum signal looks like background noise. There are two main
alternatives, Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread
Spectrum (FHSS).
