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Area Networks Sans Wires
is a brief description of the technology behind wireless
in the LAN environment, the applications and benefits it
offers over wired networks.
LANs allow workstations to communicate and access the network
using radio propagation as the transmission medium
you need dependable and fast access to information? Do you
want network performance with the freedom of mobile computing?
Do you want to access the network from anywhere in your
organization? If yes, then Wireless LANs is for you.
LANs allow workstations to communicate and access the network
using radio propagation as the transmission medium. Says
Anand Mehta, Marketing Manager, D-link India Ltd., "A
wireless LAN is an easy data communication system that uses
electromagnetic waves (radio and infra red) to communicate
information from one point to another without relying on
a physical connection. It is implemented as an option for
a wired LAN within specified premises".
as PCs were the initial driving force behind wired Ethernet
innovations in the 1980s, the wide acceptance of laptops,
palmtops, PDAs, and wireless telephony is creating an environment
that is ripe for innovation in the form of wireless Ethernet
connectivity. To find where this trend is headed for, we
need to look further into wireless LANs.
Three important WLAN technologies exist today. They are:
Sequence Spread Spectrumx
DSSS systems spread the signal energy across a relatively
wide band by increasing the occupied bandwidth. A DSSS transmitter
converts a bit stream into a symbol stream, in which each
symbol represents a certain number of bits, depending on
the phase shift keying (PSK) modulation technique.
symbol information is converted into a complex-valued signal
that is fed to the spreader. The spreader multiplies its
input signal with a pseudo noise sequence, called a chip
sequence. This multiplication creates a signal with a wider
bandwidth. The inphase and quadrature components of the
spreader output signal are fed to a quadrature modulator.
transmitter front end provides filtering, conversion to
a higher RF, and power amplification. The channel center
frequencies are 2.412 Mhz, 2.417 Mhz, 2.422 Mhz, 2.462 Mhz,
2.467 Mhz and 2.472 Mhz.
Hopping Spread Spectrum
These systems hop from narrow band to narrow band within
a wide bandwidth. FHSS wireless LAN stations send one or
more data packets at one carrier frequency, then hop to
another carrier frequency to send one or more packets, and
continue this hop transmit sequence, called slow frequency
hopping. The time these FHSS radios dwell on each frequency
is fixed. The hopping pattern appears random, but it is
actually a periodic sequence tracked by both the sender
and receiver. A FHSS transmitter converts the bit stream
into a symbol stream in which each symbol represents one
or more bits.
On the other hand Infrared (IR) systems use very high frequencies
that are just below visible light in the electromagnetic
spectrum to carry data. Like light, infra red rays cannot
penetrate opaque objects. They are either directed (line-of-sight)
or diffuse technology. Inexpensive directed systems provide
very limited range of just about three feet and are typically
used for PANs but occasionally are used in specific WLAN
applications. High performance directed IR is impractical
for mobile users and is therefore used only to implement
fixed subnetworks. Diffuse (or reflective) IR WLAN systems
do not require line-of-sight, but cells are limited to individual
another technology that will gain widespread usage in the
next few years is Bluetooth. It is a wireless personal area
networking (WPAN) technology that has garnered significant
industry support and will coexist with most wireless LAN
solutions. The Bluetooth specification is for a 1 Mbps,
small form-factor, low-cost radio solution that can provide
links between mobile phones, mobile computers and other
portable handheld devices and connectivity to the Internet.
in a wide range of devices to enable simple, spontaneous
wireless connectivity, this technology, is a complement
to wireless LANs that are designed to provide continuous
connectivity via standard wired LAN features and functionality.
The IEEE Standards board approved the 802.11 wireless LAN
standard on June 26th, 1997. The standard was published
at the end of '97 and IEEE 802.11 compliance became a minimum
requirement for any wireless LAN product. IEEE 802.11 brings
multi vendor interoperability and lower prices. The main
features of IEEE 802.11 standard are:
(because of Acknowledgement, RTS/CTS and fragmentation
channel roaming ( allowing multiple cells = higher capacity
management scheme providing longer battery life
802.11 Standard specifies the frequency band for Wireless
LAN applications as 2.4Ghz ISM band.
Latest release of IEEE 802.11 Standard specifies a maximum
bandwidth of 11 Mbps with fall back to 5.5 Mbps, 2 Mbps
and 1 Mbps throughput. In addition, the full compliance
to IEEE Standards assures not only the interoperability
with the earlier 2 Mbps Wireless LAN products but also with
expected future higher throughput wireless LAN products.
802.11 standard DSSS prescribes a single fixed 11-chip spreading
code that is used by all stations. The medium access assignment
is not made by a unique code, but rather by a listen-before-talk
carrier sensing and at a deferred transmission. All the
stations participating in a wireless network share the single-channel
do Wireless LANs Work?
Wireless LANs use electromagnetic airwaves (radio or infrared)
used 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.
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 the 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.
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 one radio frequency while
rejecting all other frequencies.
a typical wireless LAN configuration, a transmitter/receiver
(transceiver) device, called an access point, connects to
the wired network from a fixed location using standard cabling.
At a minimum, the access point receives, buffers, and transmits
data between the wireless LAN and the wired network infrastructure.
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 it is practical as long
as the desired radio coverage is obtained.
End users access the wireless LAN through wireless-LAN adapters,
which are implemented as PC cards in notebooks or palmtop
computers, as cards in desktop computers or integrated within
LAN 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
secure is a WLAN?
One of the main concerns of users of Wireless LANs is the
assumed reduction in privacy and security. Let us see how
wireless solutions address these concerns.
to all standard LAN Access Control Mechanisms offered by
network operating systems, Wireless LANs uses multiple levels
of security to prevent unauthorized access to network resources.
Wireless LAN offers up to five layers of added protection.
The following elements add to the security:
" Close Wireless System" option
encryption using a RC4 WEP
Most of the Wireless LAN products use low power Spread Spectrum
technology in sending the signal. In doing so, it transmits
data by converting the signal from digital to analog and
spreading it eleven times over the waveband. This spreading
is done using a unique code, which is built into the product.
access to the LAN does not yield intelligible results unless
the Wireless LAN product is used to decode the signal.
Wireless System" option
Wireless LAN systems provide the so-called "Close Wireless
System" option, which will prevent wireless stations
to associate with an Access Point if the SSID ( = Network
Name ) differs.
Shared Key Authentication feature allows Access Points to
verify the user as being authorized to associate to the
Access Point. It requires WEP (Wired Encryption Privacy)
to be present. The actual authentication procedure consists
of an exchange of four messages between the station and
the Access Point, allowing the Access Point to verify that
the station has the proper key.
Encryption using WEP
As an added option wireless solutions use hardware encryption
to provide added privacy to transmitted data. The traffic
between the stations will be encrypted in order to prevent
eavesdropping. Wireless LANs use encryption based on various
Wireless Solutions have the included capability to restrict
access to the infrastructure network to those stations of
which the hardware MAC address is included in a pre-loaded
filter table. Network administrators who wish to deploy
this capability will create a table of MAC addresses of
wireless stations that are allowed to have access to the
backbone. Stations with MAC addresses that do not appear
in this table are not granted access, and the traffic generated
by these stations will be filtered out. This mechanism is
known as 'Access Control' and the specific table mentioned
is called the Access Control Table.
addition to the above, user defined schemes can be added
such as user passwords on network servers. With the provided
security provisions in place, Wireless systems will have
equal or more privacy than can be expected from existing
of Wireless LAN
Wireless LAN Applications can be broadly categorized into
Campus Wireless LANs
Organizations, medical facilities, retail outlets,
warehouses, factories, research centers, educational institutions
among many others are recognizing the value of flexibility
and adaptability provided by wireless LANs.
users empowered with laptops, PDAs, palmtops can have access
to the company's intranet and Internet from any place of
their presence. A wireless way to keep them in touch with
computer services or resources is to create a wireless network
with several access points and supply the roaming staff
with portable computers equipped with wireless network interface
Managing stock control and inventory is a necessity for
any manufacturing organization and for any retail operation
of any size. But fluctuations in volume and human error
can increase the potential for more mistakes and ultimately,
wireless LAN handheld scanners, keypads and bar code readers
can be linked to databases, printers and scanners throughout
the facility. And the process is virtually paperless. Instead
of being a separate time consuming task, inventory becomes
a part of every retailer's routine, making stock and inventory
control more manageable.
LANs to difficult-to-wire-areas
Wireless LANs coexist with wired LANs and help in extending
LAN connectivity to areas with EMI/EMC problems, locations
where providing wired connections affect aesthetic qualities
of the location (showrooms, conference halls), and locations
with frequently changing environments.
LANs can also be used to provide connectivity to vehicle
mounted computers. Wireless VoIP handsets can be used by
customer service/field staff to enhance the organization's
Point-to-Point and Point-to-Multipoint Links
links are being used for providing outdoor point-to-point
and point-to-multipoint high bandwidth links connecting
different branches of an organization spread over a city.
These links can be used to set up Wireless Metropolitan
Area Networks (MANs) for e-governance or for linking various
government organizations, info kiosks, public utility places,
and so on.
point-to-multi-point links are being deployed by ISPs for
providing high bandwidth Internet connectivity to their
corporate clients. Similarly broadband service providers
and ASPs are making use of these links for offering their
Wireless LAN vendors incorporate special features such as
inbuilt router features, additional security measures, provision
for connecting outdoor antennas, high message reliability
and robust interference management features, remote monitoring
features, site survey tools, etc. which are required for
point-to-multipoint links can be used for providing the
necessary connectivity for anywhere banking, online reservation
form, and geographically dispersed counters within a city.
Rathod can be reached at email@example.com