Hawking HW7ACW, Руководство пользователя

Страница: 135 / 136

128
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
series offer the encryption function (WEP) to enhance security and
Access Control. Users can set it up depending upon their needs.
12. 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 is, 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.
13. What is Spread Spectrum?
Spread Spectrum technology is a wideband radio frequency technique
developed by the military for use in reliable, secure, mission-critical
communication 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).
14. What is WPS?
WPS stands for Wi-Fi Protected Setup. It provides a simple way to
establish unencrypted or encrypted connections between wireless
clients and access point automatically. User can press a software or
hardware button to activate WPS function, and WPS-compatible
wireless clients and access point will establish connection by
themselves. There are two types of WPS: PBC (Push-Button