Linksys WAP4400N User Manual page 47

Wireless-N Access Point with Power Over Ethernet
As the user moves on, the end node's RF transmitter regularly checks the system to determine whether it is in
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 the 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.
Would the information be intercepted while transmitting on 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, the WLAN series offers a
variety of wireless security methods to enhance security and access control. Users can set it up depending upon
their needs.
Can Linksys wireless products support file and printer sharing?
Linksys wireless products perform the same function as LAN products. Therefore, Linksys wireless products can
work with NetWare, Windows NT/2000, or other LAN operating systems to support printer or file sharing.
Appendix A: Troubleshooting 41
Frequently Asked Questions