NetComm NP5400 - Manual (Page 24)

www.netcomm.com.au Rev. 1 - YML668
Page 24 NP5400 11g Wireless Access Point User Guide
What is BSS ID?
A specific Ad-hoc LAN is called a Basic Service Set (BSS). Computers in a BSS must be
configured with the same BSS ID.
What is ESSID?
An Infrastructure configuration could also support roaming capability for mobile workers. More
than one BSS can be configured as an Extended Service Set (ESS). Users within an ESS could
roam freely between BSSs while maintaining a continuous connection to the wireless network
stations and Access Points.
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.
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 the encryption function (WEP) to enhance security and access
control. Users can set it up depending upon their needs.