Networks Essay

This essay has a total of 1377 words and 7 pages.


Wireless Local Area Networks

A wireless local area network (LAN) is a flexible data communications system implemented
as an extension to, or as an alternative for, a wired LAN. It uses radio frequency (RF)
technology, to transmit and receive data over the air, minimizing the need for wired
connections. A wireless LAN system can combine data connectivity with user mobility.

The data to be transmitted is modulated onto the radio waves, called carriers, and then
are removed from the carriers at the other end by what is called a transceiver. End users
in a wireless local area network access the network through adapters such as PC cards in
laptop notebook computers. And PCI cards in desktop computers.

These cards provide the interface linking the network operating system (NOS) and the
airwaves by means of an antenna. The wireless connection is clear to the network operating
system as well as to those using the network, and it supports applications such as
electronic mail (e-mail), access to shared peripherals, and access to multi-user databases
and applications. Wireless LANs have gained popularity in areas such as the health-care,
retail, manufacturing, warehousing and academia markets (Kurose, 2003).

Some widely known wireless technology in use in devices includes, cameras, automobiles,
security systems, and kitchen appliances. Wireless LANs use electro magnetic airwaves
(radio or infrared) to transmit information from one point to another without relying on
any physical connection (Dean, 2000). Radio waves often are referred to as radio carriers
because they simply perform the function to delivering energy to a remote receiver.
Networking firms have a range of technologies to choose from when constructing wireless
LANs. All technology comes with its own set of advantages and limitations. A narrowband
radio system transmits and receives data on a specific radio frequency. Any unwanted
crosstalk between communication channels is evaded by carefully designating different
users on different channel frequencies. (Kurose, 2003)

The commonly used wireless systems used is the spread-spectrum technology, which is a
wideband radio frequency technique developed by the military for use in reliable, secure
communication systems. This technology is developed to substitute bandwidth effectiveness
for security, reliability, and integrity (Dean, 2000). More bandwidth is consumed than in
the case of narrowband transmission, but the end result produces a signal that is louder
and easier to detect. If the receiver is not on the right frequency, a spread-spectrum
signal looks like background noise. The two types of spread-spectrum radio are frequency
hopping and direct sequence. (Behrouz, 2004)

Frequency-hopping spread-spectrum (FHSS) is a method that uses a narrow band carrier that
changes frequencies in a distinct pattern. The signal hops to a variety of frequencies,
with the exact sequence of changes, known as the hopping sequence. At any moment, the
broadcast signal uses only one frequency, or even several frequencies is not enough to
effectively affect the communication between devices. The FHSS is used between 2.4 GHz and
2.5 GHz and operates at a data rate of about 1.6 Mbs per channel. Direct sequence
spread-spectrum (DSSS) generates a bit pattern for each bit to be transmitted. This bit
pattern is called a chip or chipping code (Kurose, 2003).

Another technology that can be used in wireless networks is infrared light (IR). Infrared
systems use very high frequencies, which are those just under visible light, to transfer
data. IR cannot pass through dense objects. Therefore it must be used in line-of-sight or
with diffused technology (Dean 2000). Line of sight, or directed, technologies have a very
limited range, many times less than five feet, and are very unrealistic for people who
work in environments clustered with things which would prevent line-of-sight between
devices. Diffuse IR systems do not require line-of-sight, but units are still restricted
to one individual room.

The simplest configuration for a wireless network is an independent LAN that connects a
set of computers with wireless adapters. Any time two ore more of the wireless adapters
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