Network Computing Devices WUSB11 - Manual (Page 20)

Wireless USB Network Adapter
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Instant Wireless ® Series
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that links access points and nodes. In such a system, the user’s end node under-
takes 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 sys-
tem 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 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 devel-
oped by the military for use in reliable, secure, mission-critical communica-
tions 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 trans-
Can I play computer games with other members of the wireless network?
Yes, as long as the game supports multiple players over a LAN (local area net-
work). Refer to the game’s user guide for more information.
What is the IEEE 802.11b standard?
It is one of the IEEE standards for wireless networks. The 802.11b standard
allows wireless networking hardware from different manufacturers to commu-
nicate, provided that the hardware complies with the 802.11b standard. The
802.11b standard states a maximum data transfer rate of 11Mbps and an oper-
ating frequency of 2.4GHz.
What IEEE 802.11b features are supported?
The product supports the following IEEE 802.11b functions:
•
CSMA/CA plus Acknowledge protocol
• Multi-Channel Roaming
• Automatic Rate Selection
• RTS/CTS feature
• Fragmentation
• Power Management
What is ad-hoc mode?
When a wireless network is set to ad-hoc mode, the wireless-equipped com-
puters are configured to communicate directly with each other. The ad-hoc
wireless network will not communicate with any wired network.
What is infrastructure mode?
When a wireless network is set to infrastructure mode, the wireless network is
configured to communicate with a wired network through a wireless access
point.
What is roaming?
Roaming is the ability of a portable computer user to communicate continu-
ously while moving freely throughout an area greater than that covered by a sin-
gle access point. Before using the roaming function, the workstation must make
sure that it is the same channel number with the access point of dedicated cov-
erage area.
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