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Introduction
IEEE 802.11b
IEEE 802.11b standard specifies a WLAN that operates on the 2.4 GHz band
at data rates up to 11 Mbps. Equipment that conforms to the 802.11b
standard can interoperate with equipment conforming to faster (up to 54
Mbps) 802.11g equipment and they will interoperate. However, when
connected into the same network the 802.11g equipment will operate at the
11 Mbps limitation of the 802.11b equipment.
For media access, 802.11 wireless networks use CSMA/CA, a scheme in
which a station that intends to transmit 'listens' for traffic on the radio carrier
frequency and sends data packets if the frequency is clear. If the receiving
station receives the packet intact it sends an acknowledgement (ACK) to
confirm the packet has been received. If the transmitting station does not
receive an ACK it assumes a collision occurred and transmits again after a
random delay period.
Communication distances vary depending on the type and thickness of
material around a wireless node. The transmitter power output, the type of
antenna used and the amount of attenuation through materials also affects the
useable range. Electromagnetic noise, reflections, the amount of network
traffic, other radio devices operating in the same frequency band also affect
range and overall performance. In an infrastructure network the number of
access points and their coverage pattern also affect how well the system
operates. Typically an 802.11 device operating indoors will have a range
from 100 feet minimum to about 500 feet maximum. Outdoors, some
products, using high gain antennae may achieve line-of-sight ranges of five
miles or more.
Security is a significant concern for WLAN users. Whether security threats
originate intentionally or unintentionally, wireless systems are more
susceptible than wired systems. ES1AWB serial servers offer several security
options including WEP (Wired Equivalent Privacy), WPA (Wi-Fi Protected
Access), PEAP (Protected EAP) w/EAP-MS-CHAPv2 and others.
Manual Documentation Number: ES1AWB-2907m
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com
B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
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Chapter 1
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