touch with the original access point or whether it should seek a new one. When a node no longer
receives
acknowledgment from its original access point, it undertakes a new search. Upon finding a new
access point, it
then re-registers, and the communication process continues.
What is ISM band?
The FCC and their counterparts outside of the U.S. have set aside bandwidth for unlicensed use in
the ISM
(Industrial, Scientific and Medical) band. Spectrum in the vicinity of 2.4 GHz, in particular, is being
made available
worldwide. This presents a truly revolutionary opportunity to place convenient high-speed wireless
capabilities in
the hands of users around the globe.
What is 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).
What is DSSS? What is FHSS? And what are their differences?
Frequency-Hopping Spread-Spectrum (FHSS) uses a narrowband carrier that changes frequency
in a pattern that
is known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a
single logical
channel. To an unintended receiver, FHSS appears to be short-duration impulse noise. Direct-
Sequence Spread-
Spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern
is called a chip
(or chipping code). The longer the chip, the greater the probability that the original data can be
recovered. Even if
one or more bits in the chip are damaged during transmission, statistical techniques embedded in
the radio 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.
Will the information be intercepted while it is being transmitted through the air?
WLAN features two-fold protection in security. On the hardware side, as with Direct Sequence
Spread Spectrum
technology, it has the inherent security feature of scrambling. On the software side, WLAN offers
the encryption
function (WEP) to enhance security and access control.
What is WEP?
WEP is Wired Equivalent Privacy, a data privacy mechanism based on a 64-bit or 128-bit shared
key algorithm, as
described in the IEEE 802.11 standard.
What is a MAC Address?
The Media Access Control (MAC) address is a unique number assigned by the manufacturer to
