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Introduction
Wireless-G Exterior Access Point with Power Over Ethernet
Appendix A
To achieve true seamless connectivity, the wireless
LAN must incorporate a number of different functions.
Each node and Access Point, for example, must always
acknowledge receipt of each message. Each node must
maintain contact with the wireless network even when
not actually transmitting data. Achieving these functions
simultaneously
requires
a
dynamic
RF
networking
technology that links Access Points and nodes. In such
a system, the user’s end node undertakes a search for
the best possible access to the system. First, it evaluates
such factors as signal strength and quality, as well as the
message load currently being carried by each Access
Point and the distance of each Access Point to the wired
backbone. Based on that information, the node next
selects the right Access Point and registers its address.
Communications between end node and host computer
can then be transmitted up and down the backbone.
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.
What is WEP?
WEP is Wired Equivalent Privacy, a data privacy mechanism
based on a 40-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 any Ethernet
networking device, such as a network adapter, that allows
the network to identify it at the hardware level. For all
practical purposes, this number is usually permanent.
Unlike IP addresses, which can change every time a
computer logs on to the network, the MAC address of a
device stays the same, making it a valuable identifier for
the network.