|How WLANs Work
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 or augment networks
without installing or moving wires. Wireless LANs 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 standard 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 to several hundred feet. The access
point (or the antenna attached to the access point) is usually mounted high
but may be mounted essentially anywhere that is practical as long as the
desired radio coverage is obtained.
End users access the WLAN through wireless-LAN adapters, which are implemented
as PC cards in notebook computers, ISA or PCI cards in desktop computers,
or integrated within hand-held computers. WLAN adapters provide an interface
between the client network operating system (NOS) and the airwaves (via an
antenna). The nature of the wireless connection is transparent to the NOS.
|WLANs & Other Wireless
Wireless LANs provide all the functionality of wired LANs, but without the
physical constraints of the wire itself. Wireless LAN configurations include
independent networks, offering peer-to-peer connectivity,and infrastructure
networks, supporting fully distributed data communications. Point-to-point
local-area wireless solutions, such as LAN-LAN bridging and personal-area
networks (PANs), may overlap with some WLAN applications but fundamentally
address different user needs. A wireless LAN-LAN bridge is an alternative
to cable that connects LANs in two separate build-ings. A wireless PAN typically
covers the few feet surrounding a userÕs workspace and provides the
ability to synchronize computers, transfer files, and gain access to local
Wireless LANs also should not be confused with wireless metropolitan-area
networks (WMANs), packet radio often used for law-enforcement or utility
applications, or with wireless wide-area networks (WWANs), wide-area data
transmission over cellular or packet radio. These systems involve costly
infrastructures, provide much lower data rates, and require users to pay
for bandwidth on a time or usage basis. In contrast, on-premise wireless
LANs require no usage fees and provide 100 to 1000 times the data transmission