Atlantis Land Web Share 3G 244WN, Руководство пользователя

Страница: 127 / 133

127
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).
Question What is DSSS? What is FHSS? And what are their differences?
Answer 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.
Question Would the information be intercepted while transmitting on air?
Answer 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.
Question What is WEP?
Answer 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.