Abocom Systems, Inc. .
User Manual
Revision 1.0 • June 27, 2011 - 16 -
Appendix B: Glossary
802.11b -
The 802.11b standard specifies a wireless product 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
Adapter, 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
of 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 Adapter, 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).
SSID -
A
S
ervice
S
et
Id
entification is a thirty-two character (maximum) alphanumeric
key identifying a wireless local area network. For the wireless devices in a network to
communicate with each other, all devices must be configured with the same SSID.
