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LG GoldStream
Chapter 1 Introduction To The Wireless LAN
A wireless LAN (WLAN) is a flexible data communication system implemented as an
extension to, or as an alternative for, a wired LAN within a building or campus. Using
electromagnetic waves, WLANs transmit and receive data over the air, minimizing the
need for wired connections. Thus, WLANs combine data connectivity with user mobility,
and, through simplified configuration, enable movable LANs. WLANs have gained strong
popularity in a number of vertical markets, including the health-care, retail,
manufacturing, warehousing, and academic arenas. These industries have profited from
the productivity gains of using hand-held terminals and notebook computers to transmit
real-time information to centralized hosts for processing. Today WLANs are becoming
more widely recognized as a general-purpose connectivity alternative for a broad range
of business customers.
1.1
What's Wireless LAN?
Wireless LANs use electromagnetic airwaves (radio and infrared) to communicate
information from one point to another without relying on any physical connection. Radio
waves are often referred to as radio carriers because they simply perform the function of
delivering energy to a remote receiver. The data being transmitted is superimposed on
the radio carrier so that it can be accurately extracted at the receiving end. This is
generally referred to as modulation of the carrier by the information being transmitted.
Once data is superimposed (modulated) onto the radio carrier, the radio signal occupies
more than a single frequency, since the frequency or bit rate of the modulating
information adds to the carrier.
Multiple radio carriers can exist in the same space at the same time without interfering
with each other if the radio waves are transmitted on different radio frequencies. To
extract data, a radio receiver tunes in (or selects) one radio frequency while rejecting all
other radio signals on different frequencies.
In a typical WLAN configuration, a transmitter/receiver (transceiver) device, called an
access point, connects to the wired network from a fixed location using standar d
Ethernet cable. At a minimum, the access point receives, buffers, and transmits data
between the WLAN and the wired network infrastructure. A single access point can
support a small group of users and can function within a range of less than one hundred
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