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ABSTRACT
Wi-Fi, which stands for “Wireless Fidelity”, is a radio technology that
networks computers so they connect to each other and to the Internet without
wires .Users can share documents and projects, as well as an Internet connection
among various computer stations, and easily connect to a broadband Internet
connection while traveling. By using a Wi-Fi network, individuals can network
desktop computers, laptops and PDAs and share networked peripherals like
servers and printers.
A Wi-Fi network operates just like a wired network, without the
restrictions imposed by wires. Not only does it enable users to move around be
mobile at home and at work , it also provides easy connections to the Internet and
business networks while traveling .The technologies used in this field are one of
the best in the wireless space . It is fairly easy to set up a Wi-Fi enabled network
at home or a small office.
INTRODUCTION
Wi-Fi, or Wireless Fidelity, is freedom: it allows you to connect to the
Internet from your couch at home, a bed in a hotel room or at a conference room
at work without wires. How? Wi-Fi is a wireless technology like a cell phone. WiFi
enabled computers send and receives data indoors and out: anywhere within the
range of a base station. And the best thing of all, it‟s fast. In fact, it‟s several times
faster than the fastest cable modem connection.
However, you only have true freedom to be connected anywhere if your
computer is configured with a Wi-Fi CERTIFIED radio (a PC Card or similar
device). Wi-Fi certification means that you will be able to connect anywhere there
are other Wi-Fi CERTIFIED products-whether you are at home, the office or
corporate campus, or in airports, hotels, coffee shops and other public areas
equipped with a Wi-Fi access available.
The Wi-Fi certified logo is your only assurance that the product has met
rigorous interoperability testing requirements to assure products from different
vendors will work together .The Wi-Fi CERTIFIED logo means that it‟s a “safe”
buy.
Wi-Fi certification comes from the Wi-Fi Alliance, a nonprofit
international trade organization that tests 802.11-based wireless equipment to
make sure it meets the Wi-Fi standard and works with all other manufacturers‟
Wi-Fi equipment on the market .Thanks to the Wi-Fi Alliance, you don‟t have to
read the fine print or study technical journals: if it says Wi-Fi, it will work.
WHAT IS WI FI TECHNOLOGY?
A way to get Internet access, the term Wi Fi is a play upon the decadesold
term HiFi that describes the type of output generated by quality musical
hardware, Wi Fi stands for Wireless Fidelity and is used to define any of the
wireless technology in the IEEE 802.11 specification - including (but not
necessarily limited to) the wireless protocols 802.11a, 802.11b, and 802.11g. The
Wi-Fi Alliance is the body responsible for promoting the term and its association
with various wireless technology standards.
DIFFERENT TYPES OF WIRELESS NETWORKS.
There are basically three different types of wireless networks – WAN,
LAN and PAN:
Wireless Wide Area Networks (WWAN): WWANs are created through the use
of mobile phone signals typically provided and maintained by specific mobile
phone (cellular) service providers. WWANs can provide a way to stay connected
even when away from other forms of network access.
Wireless Local Area Network (WLAN): WLAN are wireless networks that use
radio waves. The backbone network usually uses cables, with one or more
wireless access points connecting the wireless users to the wired network. The
range of a WLAN can be anywhere from a single room to an entire campus.
Wireless Personal Area Network (WPAN): WPANs are short-range networks
that use Bluetooth technology. They are commonly used to interconnect
compatible devices near a central location, such as a desk. A WPAN has a typical
range of about 30 feet.
WIRELESS NETWORKING COMPONENTS
Wi-Fi is a friendly term for IEEE 802.11b Ethernet standard. It operates
in the unlicensed frequency band of 2.4 Ghz with a maximum data rate of 11
Mbps.
IEEE 802.11b wireless networking consists of the following components:
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.
Wireless Access Points
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.
OPERATION MODES
IEEE 802.11 defines two operating modes: Ad hoc mode and
Infrastructure mode.
AD HOC 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.
RADIO TECHNOLOGY
Wi-Fi network uses radio technology called IEEE 802.11b to provide
secure, fast, reliable, wireless connectivity. 11b defines the physical layer and
media access control (MAC) sublayer for communications across a shared,
wireless local area network (WLAN). At the physical layer, IEEE 802.11b
operates at the radio frequency of 2.45 gigahertz (GHz) with a maximum bit rate
of 11 Mbps. It uses the direct sequence spread spectrum (DSSS) transmission
technique. At the MAC sublayer of the Data Link layer, 802.11b uses the carrier
sense multiple access with collision avoidance (CSMA/CA) media access control
(MAC) protocol
DIRECT SEQUENCE SPREAD SPECTRUM
Direct Sequence is the best known Spread Spectrum Technique. A
DSSS transmitter converts an incoming data stream into a symbol stream where
each symbol represents a group of one or more bits. Using a phase varying
modulation technique, DSSS transmitter modulates or multiplies each symbol
with a noise like code called „chip‟ sequence. This is also called processing gain.
The multiplication operation in a DSSS transmitter artificially increases the used
bandwidth based on the length of chip sequence.
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 reassociate from one wireless AP to another, maintaining a continuous logical connection to the wired
network.
RANGE IN A Wi-Fi NETWORK
One of the factors that affect the range of a Wi-Fi network is the distance
of the client devices to your base station. In an open area with no walls, furniture
or interfering radio devices you may be able to get a range of 500 feet or more
from your base station to the Wi-Fi equipped computer. In fact you could get a
signal from up to a mile away depending on the antennas you use and
environmental conditions.
Many base stations can also act as relay stations for your network. For
example if you locate one Wi-Fi equipped computer 100 feet away from your base
station, another Wi-Fi computer 100 feet away in another direction and then
position your base station in the middle, you can create a network with a range of
200 feet from the Wi-Fi computer to the other.
Wi-Fi, or IEEE 802.11b, speed decreases the farther you move away
from your network. For example when you are close to the base station your WiFi
computer should be able to get the full 11Mbps data rate. Move farther away,
and depending on the environment, the data rate will drop to 2Mbps, and finally to
1Mbps. But getting just 1Mbps throughput is still a perfectly acceptable
performance level. 1Mbps is faster than most DSL and cable connections, which
means it‟s still a satisfactory high speed transmission if you are sending and
receiving e-mail, cruising the internet or just performing data entry tasks from a
mobile computer.
SECURITY
Because wireless is a shared medium, everything that is transmitted or
received over a wireless network can be intercepted. Encryption and
authentication are always considered when developing a wireless networking
system. The goal of adding these security features is to make wireless traffic as
secure as wired traffic. The IEEE 802.11b standard provides a mechanism to do
this by encrypting the traffic and authenticating nodes via the Wired Equivalent
Privacy (WEP) protocol.
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
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 pre shared 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.
WIRED EQUIVALENT PRIVACY (WEP)
WEP utilizes RC42
, a symmetric algorithm known as a stream cipher, for
encryption. A symmetric algorithm is one that relies on the concept of a single
shared key (as opposed to a public key) that is used at one end to encrypt plaintext
(the data) into cipher text (the encrypted data), and at the other end to decrypt it -
convert the cipher text back to plaintext. Thus, the sender and the receiver share
the same key, and it must be kept secret.
Stream ciphers encrypt data as it is received, as opposed to block ciphers
that collect data in a buffer and then encrypt it a block at a time. Stream ciphers
are tempting to use for applications requiring hardware implementation (i.e.
wireless LAN cards), because they can be implemented very efficiently in silicon.
WEP VULNARABILITIES
Not long after WEP was developed, a series of independent research
studies began to expose its cryptographic weaknesses. Even with WEP enabled,
third parties with a moderate amount of technical know-how and resources could
breach WLAN security. Three key difficulties were identified:
1. WEP uses a single, static shared key. It remains the same unless a network
administrator manually changes it on all devices in the WLAN, a task that
becomes ever more daunting as the size of the WLAN increases.