1. Wi – Fi
B. Chandu Avinash B.Phanindra
iii/iv B Tech iii/iv B Tech
G V P College of engg. G V P College of engg
vishakapatnam vishakapatnam
ph:9290260573 e-mail:phani_bp@yahoo.co.in
ABSTRACT
What do writing in a diary, watching
television, talking with friends, speaking on the
telephone, and reading a menu have in common?
They are all forms of communication. The word
communication may be used to identify activities
that do not involve people. Thus, communication
may be defined as the means through which
people exchange feelings and ideas with one
another. While this definition is clear and simple,
much more needs to be said. The new technology
required for space exploration has had a major
impact on communication in offices and homes.
This technology has enabled business people to
hold teleconferences with people in faraway
cities. Computers and word processors are found
in many offices. Electronic mail speeds business
messages across continents, and electronic fund
transfers give business managers great flexibility
in managing money. A new revolution in
communication was brought about with the
advent of wireless technology. There were many
developments in this field .there were infra red,
blue tooth and now Wi-Fi. This paper mainly
deals with the Wi-Fi, its networking components,
operation modes, and operation basics, devices
using it, security and finally pros, cons. 803.11b
also called Wi-Fi (Wireless-Fidelity) promises to
be the next big thing in wireless communication.
Once limited to the domain of vertical market
applications like inventory management, wireless
LAN (often represented by same name Wi-Fi,
which refers to the products based on IEEE
standard 803.11b) is now rapidly expanding into
horizontal markets. Large companies like
Microsoft, as well as many universities use Wi-Fi
extensively to provide notebook connectivity
across multi-site campuses.
WHAT IS WI-FI

2. Since 1999, wireless has simply
been based on IEEE 802.11b; Wi-Fi is an open
standard technology that enables you to build
wireless connectivity between laptops and open
area networks. Wi-Fi is trade name promulgated
by the Wireless Ethernet Compatibility
Alliance(WECA).The term Wi-Fi is used in place
of 802.11b in same way that Ethernet is used in
place of IEEE 802.3.Products certified as Wi-Fi
compliant by WECA are inter operable with each
other even if they are from different
manufacturers. A user with Wi-Fi product can use
any brand of access point with any other brand of
client hardware is build to the Wi-Fi standard.
Today’s Wi-Fi products, which
transmit in the unlicensed spectrum of 2.5GHz,
are capable of speeds up to 11 mpbs-about seven
times faster than a typical T1 connection. Wi-Fi is
the only wireless technology that will let you
seemingly roam from work to home. Having been
available in the corporate sector for some time
now, Wi-Fi is now looking towards the home and
small business.
IEEE 802.11 and IEEE 802.11b standards
802.11b extends the original
802.11 standard which includes specification for
1mpbs and 2 mpbs wireless Ethernet transmission
using spread spectrum RF signals in the 2.4 GHz
Industrial, Scientific and Medical(ISM) band. the
transmissions use 100milliwatts (MW) of
transmitter power in North America (and less in
other parts of world).In the original standard, two
different spread spectrum transmission methods
for physical layer (PHY) were defined: Direct
sequence spread spectrum (DSSS) and Frequency
hoping spread spectrum(FHSS).The 802.11b
standard extends the original DSSS and PHY
standard to provide a theoretical maximum data
rate of 11 mpbs.
Spread spectrum technology is a
modulation technique that speeds data
transmission across the entire available frequency
band in prearranged scheme. This type of
modulation makes the signal less vulnerable to
noise interference and snooping. Spread spectrum
technology also permits many users to share a
frequency band with band with minimal
interference from other users and from devices
such as microwave ovens.

3. At the MAC sub layer of the Data Link layer,
802.11b uses the carrier sense multiple access
with collision avoidance (CSMA/CA) media
access control (MAC) protocol.
A wireless station with a frame to
transmit first listens on the wireless medium to
determine if another station is currently
transmitting (this is the carrier sense portion of
CSMA/CA). If the medium is being used, the
wireless station calculates a random back off
delay. Only after the random back off delay
elapses can the wireless station again listen for a
transmitting station. By instituting a random back
off delay, multiple stations that are waiting to
transmit do not end up trying to transmit at the
same time (this is the collision avoidance portion
of CSMA/CA).
Collisions can occur and, unlike
with Ethernet, they might not be detected by the
transmitting nodes. Therefore, 802.11b uses a
Request to Send (RTS)/Clear to Send (CTS)
protocol with an Acknowledgment (ACK) signal
to ensure that a frame is successfully transmitted
and received.
• Stations
A station (STA) is a network node that is
equipped with a wireless network device. A
personal computer with a wireless network
adapter is known as a wireless client. Wireless
clients can communicate directly with each other
or through a wireless access point (AP). Wireless
clients are mobile.

4. • Wireless APs
A wireless AP is a wireless network node that
acts as a bridge between STAs and a wired
network. A wireless AP contains:
• At least one interface that connects the
wireless AP to an existing wired network (such as
an Ethernet backbone).
• A wireless network device with which it
creates wireless connections with STAs.
• IEEE 802.1D bridging software, so that it can
act as a transparent bridge between the wireless
and wired networks.
The wireless AP is similar to a cellular phone
network's base station. Wireless clients
communicate with both the wired network and
other wireless clients through the wireless AP.
Wireless APs are not mobile and act as peripheral
bridge devices that extend a wired network.
• Ports
A port is a channel of a device that can support a
single point-to-point connection. For IEEE
802.11b, a port is an association, a logical entity
over which a single wireless connection is made.
A typical wireless client with a single wireless
network adapter has one port and can support
only one wireless connection. A typical wireless
AP has multiple ports and can simultaneously
support multiple wireless connections. The
logical connection between a port on the wireless
client and the port on a wireless AP is a point-to-
point bridged LAN segment—similar to an
Ethernet-based network client that is connected to
an Ethernet switch.
OPERATION MODES
IEEE 802.11 defines two operating
modes: Ad hoc mode and Infrastructure mode.
In ad hoc mode, also known as
peer-to-peer mode, wireless clients communicate
directly with each other (without the use of a
wireless AP). Two or more wireless clients who
communicate using ad hoc mode form an
Independent Basic Service Set (IBSS). Ad hoc
mode is used to connect wireless clients when a
wireless AP is not present.
In infrastructure mode, there is at least one
wireless AP and one wireless client. The wireless
client uses the wireless AP to access the resources
of a wired network. The wired network can be an
organization intranet or the Internet, depending
on the placement of the wireless AP.

5. A single wireless AP that supports one or
multiple wireless clients is known as a Basic
Service Set (BSS). A set of two or more wireless
APs that are connected to the same wired network
is known as an Extended Service Set (ESS). An
ESS is a single logical network segment (also
known as a subnet), and is identified by its
Service Set Identifier (SSID). If the available
physical areas of the wireless APs in an ESS
overlap, then a wireless client can roam, or move
from one location (with a wireless AP) to another
(with a different wireless AP) while maintaining
Network layer connectivity.
OPERATION BASICS
When a wireless adapter is turned
on, it begins to scan across the wireless
frequencies for wireless APs and other wireless
clients in ad hoc mode. Assuming that the
wireless client is configured to operate in
infrastructure mode, the wireless adapter chooses
a wireless AP with which to connect. This
selection is made automatically by using SSID
and signal strength and frame error rate
information. Next, the wireless adapter switches
to the assigned channel of the selected wireless
AP and negotiates the use of a port. This is
known as establishing an association.
If the signal strength of the
wireless AP is too low, the error rate too high, or
if instructed by the operating system (in the case
of Windows XP), the wireless adapter scans for
other wireless APs to determine whether a
different wireless AP can provide a stronger
signal or lower error rate. If such a wireless AP is
located, the wireless adapter switches to the
channel of that wireless AP and negotiates the use
of a port. This is known as reassociation.
Reassociation with a different wireless AP can
occur for several reasons. The signal can weaken
as either the wireless adapter moves away from
the wireless AP or the wireless AP becomes
congested with too much traffic or interference.
By switching to another wireless AP, the wireless
adapter can distribute the load to other wireless
APs, increasing the performance for other
wireless clients. You can achieve contiguous
coverage over large areas by placing your
wireless APs so that their signal areas overlap
slightly. As a wireless client roams across
different signal areas, it can associate and

6. reassociate from one wireless AP to another,
maintaining a continuous logical connection to
the wired network
Devices using Wi-Fi
While Wi-Fi may be widely used
for communication between computers, there are
PDA’s that support it. It’s also possible to add
Wi-Fi support to a PDA inserting a Wi-Fi card
into the SD (secure digital) slot. PDA’s such as
the Toshiba e750 have inbuilt support for Wi-Fi
.In march 2003,Nokia announced plans to build
mobile phones that can seamlessly switch
between 802.11b and public networks.
SECURITY
The IEEE 802.11 standard defines the following
mechanisms for wireless security:
• Authentication through the open system and
shared key authentication types
• Data confidentiality through Wired
Equivalent Privacy (WEP)
Open system authentication does not provide
authentication, only identification using the
wireless adapter's MAC address. Open system

7. authentication is used when no authentication is
required. Some wireless APs allow the
configuration of the MAC addresses of allowed
wireless clients. However, this is not secure
because the MAC address of a wireless client can
be spoofed.
Shared key authentication verifies
that an authenticating wireless client has
knowledge of a shared secret. This is similar to
preshared key authentication in Internet Protocol
security (IPsec). The 802.11 standard currently
assumes that the shared key is delivered to
participating STAs through a secure channel that
is independent of IEEE 802.11. In practice, this
secret is manually configured for both the
wireless AP and client. Because the shared key
authentication secret must be distributed
manually, this method of authentication does not
scale to a large infrastructure mode network (for
example, corporate campuses and public places,
such as malls and airports). Additionally, shared
key authentication is not secure and is not
recommended for use.
Inherent in the nature of wireless
networks, securing physical access to the network
is difficult. Because a physical port is not
required, anyone within range of a wireless AP
can send and receive frames, as well as listen for
other frames being sent. Without WEP,
eavesdropping and remote packet sniffing would
be very easy. WEP is defined by the IEEE 802.11
standard and is intended to provide the level of
data confidentiality that is equivalent to a wired
network.
WEP provides data confidentiality
services by encrypting the data sent between
wireless nodes. WEP encryption uses the RC4
symmetrical stream cipher with either a 40-bit or
104-bit encryption key. WEP provides data
integrity from random errors by including an
integrity check value (ICV) in the encrypted
portion of the wireless frame.
However, one significant problem
remains with WEP. The determination and
distribution of WEP keys are not defined and
must be distributed through a secure channel that
is independent of 802.11. In practice, this is a text
string that must be manually configured (using a
keyboard) for both the wireless AP and wireless

8. clients. Obviously, this key distribution system
does not scale well to an enterprise organization.
Additionally, there is no defined
mechanism to change the WEP key—either per
authentication or at periodic intervals over the
duration of an authenticated connection. All
wireless APs and clients use the same manually
configured WEP key for multiple connections and
authentications. With multiple wireless clients
sending large amounts of data, it is possible for a
malicious user to remotely capture large amounts
of WEP cipher text and use cryptanalysis
methods to determine the WEP key.
The lack of WEP key
management, to both automatically determine a
WEP key and change it frequently, is a principal
limitation of 802.11 security, especially with a
large number of wireless clients in infrastructure
mode. The lack of automated authentication and
key determination services also effects operation
in ad hoc mode, where users might want to
engage in peer-to-peer collaborative
communication (for example, in areas such as
conference rooms).
The combination of a lack of both
adequate authentication methods and key
management for encryption of wireless data has
led the IEEE to adopt the IEEE 802.1X Port-
Based Network Access Control standard for
wireless connections.
PROS & CONS
Given the current situation, Wi-Fi
should be adopted when there is a demand for
high speeds on the move. Wi-Fi is suited for
corporate with several executives roaming around
the office with their laptops. Homes looking for
the means to share a broad band internet
connection can also consider adopting Wi-Fi. If
you are buying a laptop, look for Wi-Fi enabled
devices.
A Wi-Fi setup is rather expensive
when compared to regular LAN. Also, since Wi-
Fi drains batteries much quicker, PDA user
should avoid using it if they have the option of
Bluetooth. It is difficult to provide security in a
Wi-Fi network, as it is difficult to control the
access to the network.
CONCLUSION

9. Wi-Fi has all chances for huge
growth, a strong value proposition, multiple uses,
industry standardization; the global
standardization .the technology flaws are not
more than speed-breaker, as millions of dollars on
R&D has already poured out. Lastly, there is
plenty of space as one move from corporation-to
the home-to the campus-to the airport-to-the-hotel
and ultimately to a national wide level. This got
to be the next big thing.
REFERENCE BOOKS
1 .jeffduntemanns wi-fi guide –2nd
edition
2. wi -fi home network-raymond smith
3.wi-fi hand book –frank ohrtman

10. Wi-Fi has all chances for huge
growth, a strong value proposition, multiple uses,
industry standardization; the global
standardization .the technology flaws are not
more than speed-breaker, as millions of dollars on
R&D has already poured out. Lastly, there is
plenty of space as one move from corporation-to
the home-to the campus-to the airport-to-the-hotel
and ultimately to a national wide level. This got
to be the next big thing.
REFERENCE BOOKS
1 .jeffduntemanns wi-fi guide –2nd
edition
2. wi -fi home network-raymond smith
3.wi-fi hand book –frank ohrtman