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What is Wi-Fi
How Wi-Fi works
Security concern
Advantages and Disadvantages
What is WI-FI

This is wireless fidelity.
Wi-Fi is a wireless network protocol often used for wireless local Area networks (WLANS).
It enables multiple devices to share a single high-speed Internet connection over a distance of about 300 feet.
WLANs are local area networks of PCs without wires.
Data transmission is through air using radio frequency or infrared frequency instead of wires.
They are especially useful in educational and research institutes, offices, libraries and also can be used in any other public place like shopping malls, theatres, airports etc.

The IEEE 802.11 standard that enables the Wi-Fi technology, proposes two different ways to configure a network.
Ad-hoc network
Infrastructure network

In the ad-hoc type of network, the computer network is formed dynamically when a group of devices come together, say laptops in conference room.
The coverage area is as such small, confined to small room like conference room.
There are no fix access points.
Each node is able to communicate with every other node.
Here the nodes have to act both as the access points and stations.
The ad-hoc network uses a certain frequency for communication and any device that wants to be a member of the network must use the same frequency.

Infrastructure network, consists of a fixed infrastructure.
The network is made up of fixed access points that are used to communicate by nodes.
The fixed access points can be connected to other wired or wireless networks to extend the network coverage.
Each access point can cater to more than one node at a time.
However as the number of devices increases, the transmission rate decreases and there is need for more number of access points.

All network technologies have to security features to prevent eavesdropping, unauthorised tapping and corruption of signal.
Security loopholes can lead to loss of data, service of hacking.
Securing a wireless network is difficult compared to wire network because there are a number of physical points that can be intruded whereas in a wireless network, the network can be intruded anywhere.
Security in Wi-Fi can be provided by two ways,

Authentication is the technique by which it is verified whether a station that wants to communicate with another station or access point that has the authorization to do so or not within the coverage area of that access point.
Authentication is established between an access point and each station.

Encryption is a popular method of providing security.
In this methods the data is to be transmitted is encrypted that is coded using an encryption algorithm.
The receiver will have its equivalent decryption key and the original data is restored.
Wireless Encryption Protocol (WEP) is a standard method used for encryption.
Though it is not a completely foolproof method, it is sufficient to provide first level of security.

The primary and most important application of WLAN is for internet connection.
Multiple users can share the same high speed connection. This is very economical when the number of users is more as no additional cost is incurred for wires and other accessories.
The use of WLAN in place of wired LAN provides flexibility in up gradation of network. Whenever a new machine has to be inducted into the network all that needs to be done is configuration. No cables, no hassles. Moreover, the work place looks clean and relocation is easy. Also shared devices like printers, scanners etc can be easily ported.
WLANs are also used to transmit voice within the coverage region. LAN phones are devices that are used to communicate with each other in the coverage region. They are extremely useful for local communication within a building or between adjacent buildings, hostels, hotels etc.
No monthly rental needs to be paid like the normal telephones and installations are also simple.
The process becomes faster and the area looks tider.
It is also economical.

Free network devices from cables, allows for a more dynamic network to grown.
While connected on a Wi-Fi network, it is possible to move about without breaking the network connection.
Power consumption is fairly high compared to other standards, making battery life and heat concern.
It is not always configured properly.
It has limited range.

Wireless network will soon replace the wired networks thereby reducing the clutter of wires and providing for cleaner workspaces at office with increased portability and better security measures together with higher transmission rates and greater coverage area.
The technology promises transmission of data, including songs and movies, at sizzling speeds from any locations wirelessly.
The wonder technology will keep surprising us with its boundless possibilities in times to come.
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please read http://cisco.com/web/DK/solutions/smb/wlan.pdf for a good report of wireless lan by Cisco
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A new trend in Wireless Networking

Presented BY

D.SWATHI 02671A1282
M.MADHAVI 02671A1222

J.B.INSTITUTE OF ENGG & TECH Affiliated to JNTU, Yenkapally, Moinabad mandal, Himayat Nagar Post ,Hyderabad-75.


Wireless networking is one of the ways of establishing connectivity and creating a network by using radio frequency signal between the computers to share information. There are several ways of creating a wireless network viz., blue tooth technology, IrDA , Wireless LAN and Home- RF. Though all the technologies operate in the same frequency there is a slight difference among them in the data speeds, range ,band width and some other factors which makes them usable world-wide.

T h e present paper touches upon latest communication techniques of data transmission through wireless LAN. It also discusses the pros and cons of utilizing the spread spectrum technology used for data communication. Also the security issues which play a prominent role in a wireless LAN are highlighted.

The present paper is not an exhaustive study of the technology under focus but it is an honest endeavor to peep into the amazing world of wireless LAN which is making rapid strides in the world of computer networking.



Over the last decade advances in communication and information technology is tremendous. Networking technology has become an explosive area of growth in the computer industry. The demand for larger , faster , higher capacity networks has increased as businesses have realized the value of networking their computing systems . Initially there were wired networks where every user can connect to every other user in the network directly . As the technology advanced wireless networks came into picture .

The main reason behind developing these wireless networks is to extend the wired network using electro magnetic waves
For example, if an organization has several departments and the connectivity between these departments centralized hub is achieved by means of a wireless network .
Wireless vs wired

> Wired networks are capable of sharing information with any remote computer located in a specific network. But extending wires to every nook and corner of the network becomes extremely expensive.To avoid this wireless networking came into picture.
> Wireless networks extend the existing wired network and adds coverage to wired network's range.
> Wireless networks minimizes the cost of wiring as it requires wired connectivity only to connect the access points from the centralized hub.
> Though we find difference in the modes of operation , basic functionality of both remain same.

Wireless networking is a way of establishing a network by sending radio-frequency signals between the computing devices to share information.
Wireless Networking is one of the emerging technologies in the field of computer networking and has reached a level where it can be used for reliable communication over a network. The way it's set up will depend upon the specific requirements of an organization, but the general topologies remain the same. Moreover, the technology used for data transmission allows wireless throughput of up to 11 Mbps.
There are four types of wireless networks, ranging from slow and inexpensive to fast and expensive:
¦ Bluetooth
¦ IrDA (Infrared Data Association) -Infrared
¦ Wireless Local Area Network (WLAN)
Though all the techniques operate in the same frequency range , the effective data transfer - rate and range of each technology differs . This lead to the development of new technologies whose data transfer rate is comparatively increasing up to a maximum of 11Mbps.


Blue tooth refers to an open specification technology that enables short - range wireless voice and data communication globally. It was begun to produce low power and low cost radio interface between mobile phones and their accessories

When two blue tooth equipped devices come within 10 meters of each other .they can establish a connection.The connectivity can be extended up to 100 meters with an optional amplifier

Blue tooth is best described as a multipoint piconet structure .It uses the Frequency Hopping spread spectrum communication method and employs 1600 hops per second.. In this method of communication the data transmission is in the form of radio signals following a pre¬defined hopping sequence.
¢ Blue tooth is designed to carry voice , data and video information at up to 1Mbps.
¢ Blue tooth facilitates real - time transmissions, which makes it possible to connect any portable and stationary communication device easily.
¢ Blue tooth' s radio frequency technology does not require a direct " line - of - sight" between transmitter and receiver as in the case of infrared technology.

Bluetooth is not expected to replace the need for high-speed data networks between computers.


IrDA(Infrared Data Association) is a standard for devices to communicate using infrared light pulses. This was an experiment by IrDA which proved that a network can be established not only by radio waves but also by infrared light pulses, a faster wave frequency that is closer to visible light
¢ Since IrDA devices use infrared light, they depend on being in direct line of sight with each other.
¢ An IrDA-based network is capable of transmitting data at speeds up to 4 Mbps, and up to a short transmission range of 15 feet , and is used mainly for Personal Area Networks.
¢ IrDA technologies did not develop with interoperability and industry standardization as a primary goal, as did Bluetooth.
¢ Many proprietary implementations make IR more difficult to use.
For example, consider a computer lab in a university where the computer system of the Head lecturer is considered as the central hub and those of the students form the clients of the network .


Wireless Local Area Network (WLAN) is a flexible data communication system which uses electro magnetic waves for transmission of data and does not require a physical connection (phone lines or fiber optic cables) between individual nodes and the hub . A wireless local area network communications system is implemented as an extension to, or as an alternative for, a wired LAN. Using radio frequency (RF) technology, wireless LANs minimizes the need for wired connections. Thus, wireless LANs combine data connectivity with user mobility.


Wireless networks can be formed in two basic ways: Ad-hoc and Infrastructure.
Ad - hoc
¢ Ad - hoc is purely a wireless network.
¢ In this the computing devices communicate with each other directly over wireless without using any access points in the network.
¢ Even if it uses any access points they generally vary in features and cost depending on the requirement.
¢ All wireless cards in ad - hoc form a peer -to -peer network.
¢ Ad hoc wireless setups are usually suitable for temporary arrangements, such as in meetings, etc.
Disadvantage As the devices are directly connected the network cannot communicate with the wired network
¢ Infrastructure basically augments the existing wired network with a wireless LAN and extends the network .
¢ In this, there would be access points connecting to the network' s backbone.
¢ All wireless cards connect to a central access point that provides them connectivity with each other as well as the wired.
¢ The position of the access point should be such that the access point ranges overlap so as to provide roaming to mobile users. This way the user will get seamless connectivity as he passes from one access point to another. [ diagram]

Data transmission over wireless using Radio frequency is similar to the techniques used in an ordinary radio, AM and FM.
Basic principle
A constant carrier signal that is generated, is superimposed by another signal containing the data to be transmitted. The carrier frequency' s amplitude could be modulated by a signal (Direct Sequence), or its Frequency could be modulated (called Frequency Hopping). After modulation, the carrier signal no longer remains a single frequency, or fixed amplitude, depending upon the modulation technique.
There are two RF techniques used for data transmission in wireless LANs,
¦ Low power Narrowband
¦ Spread spectrum
Spread Spectrum is further divided into two more techniques, ¢ Frequency Hopping Spread Spectrum and
¢ Direct Sequence Spread Spectrum.


> This was the first wireless transmission system that uses radio-transmission systems to transmit and receive user information on one specific radio frequency.
> The radio signal frequency is kept as narrow as possible to minimize cost through simple radio design.
> Every wireless node communicates using a different frequency, so that there' s no cross talk with other nodes. This prevents one node from listening to others.
> So while receiving, a node will filter out all other frequencies but for the one that' s meant for it.
Narrowband technology has limited range, reliability, and security.

SPREAD SPECTRUM Introduction to Spread Spectrum

Spread spectrum is the art of secure digital communications that is now being exploited for commercial and industrial purposes. This group of modulation techniques is characterized by its wide frequency spectra. The transmitted signal bandwidth should be much greater than the information bandwidth.Then modulated output signals occupy a much greater bandwidth than the signal's baseband information bandwidth.
Inside the Spread Spectrum
Spread Spectrum signals use fast codes that run many times the information bandwidth or data rate. These special "Spreading" codes are called "Pseudo Random" or "Pseudo Noise" codes. They are called "Pseudo" because they are not real gaussian noise.

Some Important terms: Correlator

A SS correlator is a very special matched filter which responds only to signals that are encoded with a pseudo noise code that matches its own code
Generally ,an SS receiver uses a locally generated replica pseudo noise code and a receiver correlator to separate only the desired coded information from all possible signals.
An SS correlator can be "tuned" to different codes simply by changing its local code. This correlator does not respond to man made, natural or artificial noise or interference
The correlator then "spreads" out a narrow band interferer over the receiver's total detection bandwidth.
The total integrated signal density at the correlator's input determines whether there will be interference or not.
Threshold level
All SS systems have a threshold or tolerance level of interference beyond which useful communication ceases. This tolerance or threshold is related to the SS processing gain.
Processing gain
Processing gain is essentially the ratio of the RF bandwidth to the information bandwidth.
Characteristics of SS signals
SS signals are noise-like and appear wide-band which makes them possess the quality of Low Probability of Intercept

SS signals are hard to detect on narrow band equipment because the signal's energy is spread over a bandwidth of maybe 100 times the information bandwidth.
Common spread spectrum systems are of the "direct sequence" or "frequency hopping" type, or else some combination of these two types
(called a "hybrid")

Frequency Hopping Spread Spectrum

Frequency hopping is the easiest spread spectrum modulation to use.
A frequency hopped system can use analog or digital carrier modulation and can be designed using conventional narrow band radio techniques.
In Frequency Hopping, there' s a narrowband carrier signal that hops from one frequency to another in a pre-defined fashion.
It "hops" from frequency to frequency over a wide band.Both the transmitter and receiver know this hopping sequence or code sequence and therefore have to remain in synchronization in order to send and receive accurate data. and the rate of hopping from one frequency to another is a function of the information rate
Since the method hops over multiple frequencies, it forms a single logical channel used and maintained by the transmitter and receiver. To those who are not supposed to receive this signal, it appears to be wideband noise. the frequency hopper's output is flat over the band of frequencies used.
Between the two spread-spectrum technologies, DSSS (Direct Sequencing Spread Spectrum) and FHSS (Frequency Hopping Spread Spectrum), DSSS is more popular.
Direct Sequence Spread Spectrum.
A direct sequence system uses a locally generated pseudo noise code to encode digital data to be transmitted. The local code runs at much higher rate than the data rate.
Direct sequence spread spectrum systems are so called because they employ a high speed code sequence, along with the basic information being sent, to modulate their RF carrier.
The high speed code sequence is used directly to modulate the carrier, thereby directly setting the transmitted RF bandwidth.
Binary code sequences as short as 11 bits have been employed for this purpose, at code rates from under a bit per second to several hundred megabits per second.
In Direct Sequence Spread Spectrum technique, every binary ' 1' bit that' s transmitted is in the form of a sequence of ones and zeros. Every binary ' 0' transmitted uses the inverse sequence of this ' 1' bit. This redundant pattern for every bit that' s transmitted is called a
A wider chip increases the chances of data recovery by the receiver.To unintended receivers, this appears as low-power wideband noise.

A Comparative study between SS and low power narrow band
> Spread Spectrum transmitters use similar transmit power levels to narrow band transmitters
> Because Spread Spectrum signals are so wide, they transmit at a much lower spectral power density, measured in Watts per Hertz, than narrowband transmitters. This lower transmitted power density characteristic gives spread signals a big plus.
> The spread of energy over a wide band, or lower spectral power density, makes SS signals less likely to interfere with narrowband communications.
> Narrow band communications, conversely, cause little to no interference to SS systems because the correlation receiver effectively integrates over a very wide bandwidth to recover an SS signal


Most commercial part spread spectrum systems transmit an RF signal bandwidth as wide as 20 to 254 times the bandwidth of the information being sent. Some spread spectrum systems have employed RF bandwidths 1000 times their information bandwidth
Besides being hard to intercept and jam, spread spectrum signals are hard to exploit or spoof messages to a network.
SS signals also are naturally more secure than narrowband radio communications. Thus SS signals can be made to have any degree of message privacy that is desired
Spread Spectrum uses wide band, noise-like signals. Because Spread Spectrum signals are noise-like, they are hard to detect


The Low Probability of Intercept (LPI) and anti-jam (AJ) features made Spread Spectrum use in milirary applications for so many years.
Applications for commercial spread spectrum range from "wireless" LAN's (computer to computer local area networks), to integrated bar code scanner/palmtop computer/radio modem devices for warehousing, to digital dispatch, to digital cellular telephone communications, to "information society" city/area/state or country wide networks for passing faxes, computer data, email, or multimedia data.
These spread spectrum signals are widely used in radar systems

In the future

There are also "Time Hopped" and "Chirp" systems in existence. Time hopped spread spectrum systems have found no commercial application to date. However, the arrival of cheap random access memory (RAM) and fast micro-controller chips make time hopping a viable alternative spread

spectrum technique for the future. "Chirp" signals are often employed in radar systems and only rarely used in commercial spread spectrum systems.
Many newer commercial satellite systems are now converting to SS to increase channel capacity and reduce costs.
Basic components of a wireless LAN
The basic components of building a wireless LAN includes
Wireless cards
Access Points
Client Adapters
Wireless cards

This is perhaps the most essential component of a wireless LAN. These perform the same functions as Ethernet cards in a wired network.
NICs (Network Interface Cards) ,PCI cards, PCMCIA are different wireless cards that connect the computer to the WLAN. Each card has it' s own advantage.
The network-management software configures wireless connections, checks their performance and allows the network manager to change them when required.
The wireless cards can be run in either one of two modes: ad hoc or infrastructure. In ad hoc mode wireless cards are able to communicate with each other without using an access point, and form a kind of Peer to Peer network. In infrastructure mode these cards communicate with an access point

Access points
Accesspoints are considered to be the most important component of the network
Access points serve as transmitters / receivers connecting the wireless clients to the wired network by bridging both the wired and wireless protocols.
The number of clients an access point can serve can vary. They extend the range of peer-to-peer WLAN by working as a repeater, doubling the distance between wireless clients
All PCs that are equipped with a wireless NIC and within the microsell of the access point get connected to the wired network without the use of cable thus creating a WLAN.
A number of access points can be connected to the wired network to allow clients to roam through the network.ensuring unbroken connectivity as long as roaming users stay in range of at least one access point.
An access point can transmit data upto 300 feet (100 meters approx.) depending on the obstacles in the environment.
Directional antennas are used when the distance between two WLANs is a mile or more.
Three kinds of Access points are currently available.
Point to point.: These are used to connect two LAN segments together.
Point to multi-point: Here all bridged units communicate with each other wirelessly.
Repeater:.In the first two modes, bridging units talk only to each other, and do not connect to wireless clients. These are also usually the most expensive.
Access points control traffic as they buffer , transmit and receive the data flowing between sender and receiver .
Client Adapters
WLAN adapters acts as interface between the client network operating system and the data arriving from access points.
The network operating system recognize wireless data as it would recognize Ethernet data.
Basic functionality of these adapters remain the same both in wired and wireless LAN.
In the future
Some other based products have also started appearing in the market. These include wireless Internet cameras, presentation gateways, and print servers.
With more such devices coming into the market, networks will become even more flexible.


+ WLAN configurations can be simple or complex. At the most basic level, two PCs with wireless adapter cards can set up an independent network, peer-to-peer wireless LAN, whenever they are in range of one another.
+ An access point's radius is called as microcell. The best way to extend the radius of a wireless LAN is to install several access points.
+ Overlapping microcells create seamless access as we roam from one microcell to another.
+ In a setting with overlapping microcells , mobile devices and access points frequently check the strength and quality of transmission and wireless LAN system hands-off roaming users to the access points with strongest and highest quality signal.
+ Adapters and access points work together and follow a series of steps to determine which access point should accept a hand -off between cell sites. This exchange is based on available bandwidth , traffic ,signal strength and quality.
+ When an adapter detects one signal getting weaker and another getting stronger , it requests a switch , and the new access point accepts a hand- off from the previous access point.
+ More users can cause air-wave congestion which can lead to slower throughput.
+ Throughput improves when ever there is less interference, whether from internal user or external sources and when mobile users are closer to the access points, hence range is also important.The type of WLAN systems determines the type of throughput.
+ Thus effective high speed data transmission is achieved through Wireless Local Area Network technology.

WLAN provide enormous flexibility, but they also can be a potential open door into the network..
Unauthorized access to networks by way of a wireless access point can be all too easy if you don't employ measures to protect your data. The security technologies offer increasing levels of protection for wireless businesses.
WLANs have their roots in military technology, so, from their inception, security has been an important priority
A WLAN solution can support multiple layers of security.
To gain access to the network, you must know the network ID of an access point. Once a user is associated with an access point, they have the same security as provided on the wired network: authentication with login ID and password, and so on.
In addition, WEP (Wired Equivalent Privacy), a standards-based security protocol for wireless networks, may be enabled, providing further security.
Some WLAN products offer multiple layers of security, like access point locking, user authentication, domain identification and option to scramble wireless data transmissions using encryption.

WLAN is highly reliable, and maintains its integrity which depend on a variety of factors like number of users.
> While WLANs provide installation and configuration flexibility and the freedom inherent in network mobility, customers may have some concerns when considering WLAN systems, including: throughput, security, ease of use, and power source issues.
> It is highly secure and thus it could find in various applications.
> It's range can be increased by increasing the access points which is not possible with other wireless technologies.

> It is highly expensive yet used in various fields of applications.
> Systems using different frequency bands do not interoperate, even if they both employ the same technology and systems from different vendors may not interoperate even if they both employ the same technology and the same frequency band, because of differences in implementation by each vendor.
> To counter these issues, an interoperability alliance organization, WECA (Wireless Ethernet Compatibility Alliance), is formed by WLAN providers. WECA' s mission is to certify interoperability of High Rate products and promote that standard for the enterprises, small businesses and homes.
> Products bearing the WECA logo will interoperate with products from other manufacturers also bearing the WECA logo


To date, wireless LANs have been primarily implemented in vertical applications such as manufacturing facilities, warehouses, and retail stores and the future will see business segments like healthcare facilities, educational institutions, and corporate enterprise office spaces benefit with the growth of WLANs.
As wireless networking is also being used in home networking Home RF is considered as one of the best emerging technologies in Home networking.


The HomeRF Working Group (RF stands for radio frequency) was an alliance of businesses that developed a standard called Shared Wireless Access Protocol (SWAP). SWAP supports both voice and data communication .SWAP transmits and receives data at a rate of 1 or 2Mbps .
SWAP is inexpensive and easy to install. It requires no additional wires, no access point. It has good power management and allows up to 127 devices per network, also allows multiple networks in the same location. Security is also robust.
SWAP has a limited range (75 to 125 ft / 23 to 38 m). It's not compatible with FHSS devices. Physical obstructions (walls, large metal objects) can interfere with communication and is difficult to integrate into existing wired networks
Because of this lack of an access point, HomeRF networks are significantly cheaper than the other viable wireless network, WECA's Wi-Fi. However, to send large amounts of data (like video) back and forth, SWAP speed is probably adequate for most home use, and the freedom of no wires can be quite appealing.
WECA and Wi-Fi

The Wireless Ethernet Compatibility Alliance (WECA) has gone in a completely different direction from HomeRF. Targeted more at office use than home networks, Wi-Fi (for "wireless fidelity", like Hi-Fi for "high fidelity" in audio equipment).This specification drops FHSS and focuses on DSSS because of the higher data rate it can attain. Though it may occasionally slow down, this keeps the network stable and very reliable.
¢ It has a long range (1,000 ft / 305 m in open areas, 250 to 400 ft / 76 to 122 m in closed areas)
¢ It's easily integrated into existing wired-Ethernet networks.

¢ It's compatible with original 802.11 DSSS devices. Here are the disadvantages:
¢ It's expensive.
¢ It can be difficult to set up.
¢ Speed can fluctuate significantly.


Blue tooth Wireless LAN Home- RF Infrared
Frequency 2.4GHz 2.4GHz 2.4GHz IR band
Data rate 1Mbps 11Mbps 1.6Mbps 4Mbps
Range 10m 150m 45m 5m
Standard Blue tooth IEEE Shared Wired Access Protocol IrDA
Communication technique FHSS DSSS FHSS -
Usage - model Cable
replacement High - speed
access Low- speed , low cost voice and data
networking Point- to-point data transmission

The future

With the recent adoption of new standards for high-rate WLANs, mobile users can realize levels of performance, throughput, and availability comparable to those of traditional wired Ethernet. As a result, WLANs are on the verge of becoming a mainstream connectivity solution for a broad range of business customers.

There' s ongoing development in the area of wireless LANs. New standards are being developed by the IEEE to improve the performance and throughput. For instance, the latest draft standard, the 802.11g, is trying to take the throughput in wireless LANs to 20+ Mbps, and that too in the 2.4 GHz band. Given such a development, wireless LANs seem to be a promising technology for the future.

Our world is rapidly changing -- computers have gone from mainframes to palmtops. Radio communications has gone from lunchbox sized (or trunk mounted/remote handset car phone) to cigarette-pack-sized micro-cellular telephone technology. The technical challenges of this progress are significant. The new opportunities created by this new technology are also significant. We've talked here about some of the very basic principles in spread spectrum and talked about evolving career opportunities -- isn't it time somebody did something about moving forward in the new millennium

Introduction to Methods of Wireless networking.
What is Wireless LAN
Data Transmission techniques
Spread Spectrum technologies.
FHSS ( Frequency Hopping Spread Spectrum) and DSSS (Direct Sequence Spread Spectrum).
Basic components of a wireless LAN.
How wireless LAN works
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Peer-to-Peer or ad-hoc wireless LAN

An ad-hoc network is a network where stations communicate only peer to peer (P2P). There is no base and no one gives permission to talk. This is accomplished using the Independent Basic Service Set (IBSS).
A peer-to-peer (P2P) network allows wireless devices to directly communicate with each other. Wireless devices within range of each other can discover and communicate directly without involving central access points. This method is typically used by two computers so that they can connect to each other to form a network.
If a signal strength meter is used in this situation, it may not read the strength accurately and can be misleading, because it registers the strength of the strongest signal, which may be the closest computer.

A bridge can be used to connect networks, typically of different types. A wireless Ethernet bridge allows the connection of devices on a wired Ethernet network to a wireless network. The bridge acts as the connection point to the Wireless LAN.
Wireless distribution system
A Wireless Distribution System is a system that enables the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required. The notable advantage of WDS over other solutions is that it preserves the MAC addresses of client packets across links between access points.[4]
An access point can be either a main, relay or remote base station. A main base station is typically connected to the wired Ethernet. A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay base station. A remote base station accepts connections from wireless clients and passes them to relay or main stations. Connections between "clients" are made using MAC addresses rather than by specifying IP assignments.

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Wireless LAN (WLAN)

Wireless LAN (WLAN) is a flexible data communication system implemented as an extension to a wired LAN within a building or campus. WLANs transmit and receive data over the air by electrical signals, minimizing the need for wired connections. The advent of WLAN opened up a whole new definition of what a network infrastructure can be. No longer does an infrastructure need to be solid and fixed, difficult to move and expensive to change. Instead it can move with the user and change as fast as the organization does.
Thus WLANs combine data connectivity with user mobility. Today it provides wireless access to vital network resources such as large, multi location enterprises, small and medium enterprises as well as hotels and hospitals, airports and homes. They are being widely recognized as viable, cost effective general purpose solution in providing real-time access to information and are reshaping the local area network landscape.
Wireless LANs are based on a set of technologies known by the IEEE specification number, 802.11 or by its synonymous trademarked name, Wi-Fi™ and is gaining popularity due to fact that it operates in the unlicensed ISM(Industrial Scientific & Medical) band (2.40 GHz to 2.484 GHz, 5.725 GHz to 5.850 GHz)
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WLAN-Wireless LAN

The term “Computer Network” to mean a collection of autonomous computers interconnected by a single technology .By this interconnection they are able to exchange information. Local Area Networks are privately owned networks within a single building or campus of few kilometers in size. In a traditional LAN we are connecting computers to the network through cables. But the wireless local area network (WLAN) is a flexible data communications system that can use either infrared or radio frequency technology to transmit and receive information over the air. Here each computer has a radio Modem and Antenna with which it can communicate with other systems. One important advantage of WLAN is the simplicity of its installation. Installing a wireless LAN system is easy and can eliminate the needs to pull cable through walls and ceilings. WLANs allow greater flexibility and portability than do traditional wired local area networks (LAN). 802.11 was implemented as the first WLAN standard. It is based on radio technology operating in the 2.4 GHz frequency and has a maximum throughput of 1 to 2 Mbps.
Unfortunately, wireless networking is a double-edged sword. WLANs use electromagnetic waves to transmit information, the radio waves can easily penetrate outside the building, it’s a risk that the network can be hacked from the parking lot or the street. So it’s very important to put enough attention on the WLANs security aspects. With wireless networking, there is no physical security. The radio waves that make wireless networking possible are also what make wireless networking so dangerous. An attacker can be anywhere nearby listening to all the traffic from the network. By properly engineering and using your wireless network, we can keep attackers at bay.


As we know “Computer Net work” is the linking of two or more computers within a well defined area. Of the common networks used today Local area networks(LAN) serve to provide solutions of the most general interest .A wireless Local area network (WLAN ) is a flexible data communication system implemented as an extension to ,or as an alternative for a wired LAN. As the name suggests a wireless LAN is one that makes use of wireless transmission medium, i.e. wireless LAN transmits and receives data over air, and minimizing the need for the wired connection. Thus wireless LAN combines data connectivity with user mobility. WLANs also allow greater flexibility and portability than traditional wired LAN which requires a wire to connect a user computer to the network. The initial cost for WLAN hardware can be higher than the cost of wired LAN hardware. But the overall installation expenses and lifecycle cost can be significantly lower. With WLAN users can access shared information without looking for a place to plug in, and network managers can setup or argument networks without installing or moving wires. There are many reasons people choose to deploy a wireless LAN, Increase the productivity due to increase mobility, Lower infrastructure cost compared to wired networks, Rapid deployment schedules

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802.11 Wireless LAN

Provides network connectivity over wireless media
An Access Point (AP) is installed to act as Bridge between Wireless and Wired Network
The AP is connected to wired network and is equipped with antennae to provide wireless connectivity
Range ( Distance between Access Point and WLAN client) depends on structural hindrances and RF gain of the antenna at the Access Point
To service larger areas, multiple APs may be installed with a 20-30% overlap
A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP (Hand-Off)
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Guided by Submitted by
Mr. G. T. Chavan Dharmrajsinh. V.


I'm not pretending to teach a course on Wireless LAN. I guess that many books explain the subject in more details and accuracy than me (anyway, I hope). I just feel that many users of Wireless LANs don't really know what is inside their magic piece of kit and are curious about it. I hope that this document will help you to understand a bit more of the different technological aspects and compare the different Wireless LANs functionalities.
While working on the Wavelan driver and the Wireless Extensions, I've gathered much information trying to understand how it works. The vendors documentation and web sites have been also very helpful, many of them really try to explain the technologies behind their products and provide white papers. The Net contains also a lot of papers and reports on the subject of wireless LANs and radio communications.

for more
http://topicideas.org/how-to-wireless-la...ty-seminar and presentation-report
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A wireless LAN (WLAN) is a flexible data communication system implemented as an extension to, or as an alternative for, a wired LAN within a building or campus. Using electromagnetic waves. WLANs transmit and receive data over the air, minimizing the need for wired connections. Thus, WLANs combine data connectivity with user mobility, and, through simplified configuration, enable movable LANs.
Wireless LAN provides a new layer of flexibility and serves to environments and to users that cannot serve by the traditional LAN. For users who are becoming highly mobile within their building environments, the wireless LAN could be the most effective way to couple them to their information and communication services. In wireless LAN the user must stay with in contract space provided by the wireless communication system.
Over the past few years, wired LANs have lost their need and interest to wireless LANs due to the fact that some applications could not implement LANs. For instance, consider a warehouse where there is a need to track vehicles, movements of goods, locations etc., in support of logistics and distribution activity. Wiring LANs, the Moving users can be in direct two-way contact with the full resources of the enterprises information systems. Similarly, situations in which people have to move around to various locations to perform their work are candidates for wireless LANs. Such situations would include manufacturing stations, researchers, testers, and health care providers.
Wireless LANs can also move to higher power plateaus, which will extend their distances from hundreds of feet to several tens of thousands of feet. In fact, with multiple capability of some of the wireless networks, this technology may be more far reaching than the wired world. Adding wireless satellite broadcasting would give you a global capability. These alternatives can make the wireless LAN world more flexible and support longer distances than the other options.
The simplest WLAN configuration is an independent (or peer-to-peer) WLAN that connects a set of PCs with wireless adapters. Any time two or more wireless adapters are within range of each other, they can set up an independent network. These on-demand networks typically require no administration or reconfiguration.
Access points can extend the range of independent WLANs by acting as a repeater. In infrastructure WLANs, multiple access points link the WLAN to the wired network and allow users to efficiently share network resources. The access points not only provide communication with the wired network but also mediate wireless network traffic in the immediate neighborhood. Multiple access points can provide wireless coverage for an entire building or campus.
The IEEE 802.11 standard represents the state of the art in wireless LANs. This standard support's Direct Sequencing Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS) and Infrared technology.
In wireless LANs the user's or clients access the data or information form the server through the Access Point. This access point is working as a bridge between Ethernet LAN and wireless LAN. The media between client and access point is space.
The data is to be transferred in the form of Microwaves or Spread Spectrum or Infrared technique. In all this the transmitters and receivers handle the data transfer between client and server.
Most wireless LAN systems use spread-spectrum technology, a wide band radio frequency technique developed by the military for use in reliable, secure, mission-critical communications systems. Spread-spectrum is designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrow band transmission, but the tradeoff produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to the right frequency, a spread-spectrum signal looks like background noise. There are two types of spread spectrum radio:
Frequency-hopping spread-spectrum (FHSS) uses a narrow band carrier that changes frequency in a pattern known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise.
Direct-sequence spread-spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low-power wide band noise and is rejected (ignored) by most narrow band receivers.
Infrared (IR) systems use very high frequencies, just below visible light in the electromagnetic spectrum, to carry data. Like light, IR cannot penetrate opaque objects; it is either directed (line-of-sight) or diffuse technology. Inexpensive directed systems provide very limited range (3 ft) and typically are used for LANs 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 sub networks. Diffuse (or reflective) IR WLAN systems do not require line-of-sight, but cells are limited to individual room.
Microwave WLANs use the frequencies in the 18GHz to 24GHz ranges to encapsulate and transfer the LAN data packets. They are capable of a multiplexed traffic load and can be used beyond building limits. if permitted by the license. The wireless LAN microwaves are a specialized part of the microwave spectrum, which is licensed for limited distance lower power operation.
The distance from microwave LANs depends on the number of hops between transceivers. The single - hop distance is on the order of 80 to 100 feet. There can be as unlimited number of hops in the overall network as long as the single hops confirm to the distance limitations. Long distance microwave towers can send their waves to around 30 miles, depending upon the size of the tower. This is done with high-power microwaves, where as the wireless LAN systems use for lower power and must limit their distance.
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Wireless Networks
A network could be defined as an interconnected collection of autonomous computers. Two computers are said to be interconnected if they are able to exchange information.
The type of this connection could be referred to as the communication media. It could be via a copper wire, using fiber optics or even communication satellites could also come into the scene.
If the communication medium between the computers of the network is without wires (i.e., infrared rays or some other similar mode of communication), such a network could be referred to as wireless network.
History of Wireless Networks:
The first indication of wireless networking dates back to 1800 and before when Indians used smoke signals as a means of transferring the information. Later evolution of communication means from messengers on horse back to telephones and public and private radio communications marked the progress of communication technology.
Computer networks and radio communications (which, of course used the wireless media) were first brought together in 1971 at the University of Hawaii as a research project and implimentation called ALOHANET. This project and implimentation enabled computer sites at seven campuses spread over four islands to communicate with a central computer situated at Oahu. U.S. military used this technology via DARPA to support tactical communication at warfields.
Though the advent of wired Ethernet technology, with it’s hopping 10Mbps speed marked a big blow to the development of wireless networks, ham radio users kept this technology alive.
In 1985, the Federal Communications Commission (FCC) made the com
mercial development of radio-based LAN components possible by authorizing the public use of the Industrial, Scientific and Medical (ISM) bands. This has had a dramatic effect on the wireless industry, prompting the development of wireless LAN components.
During the late eighties, the decreasing size of computers from desktop machines to laptops allowed employees to take their computers with them around the office and on business trips. In 1990, NCR began shipping WaveLAN, one of the first wireless LAN adapters for PCs. Further development was concentrated on meeting the mobility needs of the market. However due to their high cost, initial implementations and lack of standards limited widespread use of wireless networks.
• The 802 Working Group of Institute for Electrical and Electronic Engineers (IEEE), which is responsible for developing LAN standards such as Ethernet and token ring, has developed a standard for wireless LANS under 802.11. End users and network managers have had a difficult time showing a positive business case for purchasing wireless LAN components in the office unless there is a requirement for mobility. Sensing a bleak market for wireless LAN products, wireless LAN vendors began equipping their wireless LAN components in 1995 with directional antennas to facilitate point-to-point connections between buildings located within the same metropolitan area (wireless MANs).
• The most widely accepted wireless network connection has been wireless WAN services, which began surfacing in the early 90s. Companies such as ARDIS and RAM Mobile Data were first in selling the wireless connections between portable computers, corporate networks and the Internet. This service enables employees to access e-mail and other information services from their personal appliance without using the telephone system when meeting with the customers, traveling in the car, or staying in a hotel room.
• Narrowband Personal Communications Services (PCS), a spectrum allocated at 1.9 GHz, is a new wireless communications technology offering wireless access to WWW, e-mail, voice mail, and cellular phone service. These developments paved way for various other related developments such as Bluetooth Technology and Wireless Application Protocol Services.
Architecture of Wireless Nerworks
Networks perform many functions to transfer information from source to destination such as a bit pipe for data transmission, sharing of a common medium by medium access techniques, synchronization and error control mechanisms as well as routing mechanisms. Network architecture describes the protocols, major hardware and software elements that constitute the nwetwork.
There are two views of a computer architecture:
a) Logical View:
A logical architecture defines the network’s protocols – rules by which the two entities communicate. One popular logical architecture is the 7-layer Open System Interconnection (OSI) Reference Model, developed by International Standards Organization (ISO). The OSI layers provide the following network functionality:
Layer 7 – Application Layer: Establishes communication with other users and provides services such as file transfer and e-mail to the end users of the network.
Layer 6 – Presentation Layer: Negotiates data transfer syntax for the application layer and performs translations between different datatypes, if necessary.
Layer 5 – Session Layer: Establishes, manages, and terminates sessions between applications.
Layer 4 – Transport Layer: Provides mechanisms for the establishment, maintenance, and orderly termination of virtual circuits, while shielding the higher layers from the network implementation details.
Layer 3 – Network Layer: Provides the routing of packets from source to destination.
Layer 2 – Data Link Layer: Ensures Synchronization and error control between two entities.
Layer 1 – Physical Layer: Provides the transmission of bits through a communication channel by defining electrical, mechanical and procedural specifications.
Wireless LANs and MANs function only within the Physical and Data Link Layers, which provide the medium, link synchronization and error control mechanisms. Wireless WANs provide these first two layers as well as Network layer routing.
b) Physical architecture of a wireless network:
The physical components of a wireless network implement the physical, data link and network layer functions. The Network Operating System (NOS) located on client and server machines, communicates with the wireless Network Interface Card (NIC) via driver software, enabling the applications to utilize the wireless network for data transport.
Slide 2
Features of physical architecture:

End User Appliances: It is a visual interface between the user and the network. Various end user appliances are Desktop workstations, laptops, palmtops, pen based computers, PDAs and pagers.
Network Software: A wireless network supports the NOS and it’s applications, such as word processing, databases, and e-mail, enabling the flow of data between all components.
Wireless Network Interface: It’s function is to couple the digital signal from the end-user appliance to the wireless medium, which is air, to enable an efficient data transfer between sender and receiver. This process includes modulation and amplification.
It also manages the use of air for communications and synchronization through a carrier sense protocol. This protocol enables a group of wireless computers to share the same frequency and space. According to the protocol, to avoid two people speaking at the same time, you should wait until the other person has finished talking. Also, no one should speak unless the room is silent.
Wireless networks handle error control by having each station check incoming data for altered bits. The interface also includes the software driver that couples the client’s applications or NOS software to the card.
Antenna: Antennas come in many shapes and sizes. They have the following characteristics:
Propagation pattern, radiation power, gain, bandwidth.
They are of two types unidirectional and omni directional.
The communications channel: All information systems employ a communications channel along which information flows from source to destination.
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What is WLAN ?
 WLAN is a wireless local area network which is the linking of two or more computers or devices without using wires.
 uses radio waves for communication between devices in a limited area.
 WLAN is based on the IEEE 802.11 standard.
Why WLAN ?
• WLAN are implemented as an extension to wired LANs and provide connectivity between a wired network and the mobile user.
• It’s mainly used in college campuses, office buildings, and many public areas .
• Its benefits are:
 Basic service set (BSS) : It is a set of all stations that can communicate with each other.
 There are two types of BSS: Independent BSS and infrastructure BSS.
a) Independent BSS (IBSS) is an ad-hoc network that contains no access points. So, it can not connect to any other basic service set
b) Infrastructure BSS has an access point. So, it can communicate with other BSSs through access points.
 Extended Service Set (ESS): it is a set of connected BSSs .
 Each ESS has an 32-byte ID called the SSID (service set identifier).
 Access points in an ESS are connected by a distribution system.
WLAN technology
• There are three unlicensed bands: 900 MHz, 2.4 Ghz combinedly called “ISM”(Industry Scientific And Medical )and 5.7 GHz called “UNII”(Unlicensed National Information Infrastructure) which implement WLAN.
• Frequencies for these bands are as follows:
900-MHz band: 902 MHz to 928 MHz.
2.4-GHz band: 2.4GHz to 2.4835 GHz. (In Japan, it extends to 2.495 GHz.)
5.7-GHz band: 5.725 GHz to 5.825 GHz.
Wireless standards
 There are several different wireless standards in the market today
Wi-Fi certification
802.11b standard
802.11a standard
802.11g standard
 Wi-Fi Certification :This certification assures the consumer that the wireless LAN device will work with other Wi-Fi devices.
Wireless standards
WLAN Devices

 Wireless access point: handles the ingoing and outgoing traffic from and to wireless LAN users.
 acts as the gateway for wireless users to access a wired LAN
 It contains following security features :
 Built-in firewall
 Network Address Translation (NAT)
 Wired Equivalent Protection (WEP)
 Wireless Ethernet pc card : It is a slim Ethernet card that connects a notebook computer to a wireless network.
 Wireless PCI Adapter : It connects desktops to wireless network.
 Wireless USB adapter : provide high-speed wireless networking for USB-enabled desktops or notebooks
 Wireless range extenders : It is an indoor omni-directional antenna that can be attached to several of the WL products to increase signal strength.
WLAN Security
• To secure a WLAN, these steps are required:
Control and Integrity
Privacy and Confidentiality
Intrusion Detection System (IDS)
Protection and Availability
In 802.11 networks, clients can authenticate with an AP using one of the following methods:
open authentication - No authentication method is used. Any client is offered open access to the AP.
pre-shared key (PSK) authentication - It uses a long Wireless Equivalence Protocol (WEP) key that is stored on the client and the AP. If the keys match, the client is permitted to have access.
 WLAN may not be desirable due to some following limitations:
 Security - Wardrivers can easily crack into wireless network as there is no physical protection for data packets
 encryption technologies like WPA (Wi-Fi protected Access) must be used.
 Range - The typical range of a common 802.11g network with standard equipment is of the order of tens of meters.
 For extra range, additional APs required which costs high.
 Speed – the speed on most wireless network (1-54 Mbps) is reasonably slow compared to the wired networks (10Mbps- 10Gbps).
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Wireless local area networks (WLAN) are expected to be a major growth factor for communication networks in the up-coming years. They are expected to provide a transparent connection for mobile hosts to communicate with other mobile hosts, and wired hosts on the wired LAN and broadband networks. Recently there have been two WLAN project and implimentations undergo standardization process: the IEEE 802.11 and the ETSI HIPERLAN. Most of the existing study of the two MAC protocols focused on simulation results, and none of them has formally analyzed the hidden-terminal effect, which is both crucial and unavoidable in wireless/mobile environment. In the first part of this paper, we formally analyze the hidden-terminal effect on HIPERLAN. Through mathematical analysis, we formulate network throughput under hidden-terminal influence in terms of the original (clear-channel) throughput, hidden-terminal probability, and other protocol parameters. We show that when hidden probability is greater than zero, the achievable throughput is reduced by more than the percentage of hidden probability. In the second part of the paper, we evaluate and compare the two WLAN MAC protocols by simulation on the effect of hidden terminals on (1) network throughput, (2) real-time voice delay, and (3) number of voice and data stations supported while guaranteeing delay for voice. We also evaluate how well the two MAC protocols support real-time traffic while considering the effects of frame size and other network parameters, and measure (1) the distribution of voice delay and (2) number of voice and data stations supported while guaranteeing their quality of service. We found that, comparing with IEEE 802.11, HIPERLAN provides real-time packet voice traffic with shorter delay, and at the same time provides the non-real-time packet data with higher bandwidth. Wireless LANs have become popular in the home due to ease of installation, and the increasing popularity of laptop computers. Public businesses such as coffee shops and malls have begun to offer wireless access to their customers; sometimes for free. Large wireless network project and implimentations are being put up in many major cities: New York City, for instance, has begun a pilot program to cover all five boroughs of the city with wireless Internet access
A wireless local area network (WLAN) links two or more devices using some wireless distribution method (typically spread-spectrum or OFDM radio), and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network
1. Introduction
Wireless LANs are a boon for organizations that don't have time to setup wired LANs, make Networked temporary offices a reality and remove the wire work that goes on in setting LANs.They are reported to reduce setting up costs by 15%. But, with these benefits come the Security concerns. One doesn't need to have physical access to your wires to get into your LANs now. Any attacker, even though sitting in your parking lot, or in your neighboring building, can make a mockery of the security mechanisms of your WLAN.If you don't care about security, then go ahead; buy those WLAN cards/ Access Points. But, if you do, watch out for the developments on the security front of 802.11.As this report and many such others tell, contrary to 802.11’s claims, WLANs have very little security. An attacker can listen to you, take control of your laptops/desktops and forge him to be you. He can cancel your orders, make changes into your databases, or empty your credit Cards.
So, what is the remedy?
Don't trust anybody!!!
Think like an attacker and take proper countermeasures. Have dynamic system administrators. Those attackers won't be lucky every time! The key is, be informed!
2. About Wireless LAN
Wireless LANs

A wireless local area network (WLAN) is a local area network (LAN) that doesn't rely on wired Ethernet connections. A WLAN can be either an extension to a current wired network or an alternative to it. Use of a WLAN adds flexibility to networking. A WLAN allows users to move around while keeping their computers connected.WLANs has data transfer speeds ranging from 1 to 54Mbps, with some manufacturers offering proprietary 108Mbps solutions. The 802.11n standard can reach 300 to 600Mbps.Because the wireless signal is broadcast so everybody nearby can share it, several security precautions are necessary to ensure only authorized users can access your WLAN.A WLAN signal can be broadcast to cover an area ranging in size from a small office to a large campus. Most commonly, a WLAN access point provides access within a radius of 65 to 300 feet.
3. WLAN types
3.1 The private home or small business WLAN

Commonly, a home or business WLAN employs one or two access points to broadcast a signal around a 100- to 200-foot radius. You can find equipment for installing a home WLAN in retail stores like Office Max, Radio Shack, Target, and Wal-Mart, among others.
With few exceptions, hardware in this category subscribes to the 802.11a, b, or g standards (also known as Wi-Fi). Home and office WLANs adhering to the new 802.11n standard are appearing. Also, because of security concerns, many home and office WLANs adhere to the Wi-Fi Protected Access 2 (WPA2) standard.
3.2 The enterprise class WLAN
This type employs a large number of individual access points to broadcast the signal to a wide area. The access points have more features than equipment for home or small office WLANs, such as better security, authentication, remote management, and tools to help integrate with existing networks. These access points have a larger coverage area than home or small office equipment, and are designed to work together to cover a much larger area. Such equipment adheres to the 802.11a, b, g, or n standard, though it's becoming common that equipment subscribes to security-refining standards, such as 802.1x and WPA2
3.3 Wireless WAN (wide area network)
Although a WAN by definition is the exact opposite of a LAN, wireless WANs (WWANs) deserve brief mention here, especially because the distinction is becoming less and less obvious to end users.
WANs used to exist in order to connect LANs in different geographical areas (see What is the difference between a LAN, a MAN, and a WAN, and what is a LAN connection?). Until recently, this was also the case for WWANs. Now, cellular phone companies, such as Verizon (Broadband Access) and AT&T (Broadband Connect), offer WWAN technology that the end user can access directly.
The cellular WWANs use cellular data technology to cover extremely wide areas. Cellular WWAN data transfer rates are considerably slower than wireless LANs, with most advertising between 50Kbps to 2Mbps (compare this to dial-up speeds, which are around 56Kbps). Cellular WWANs rely on coverage by the cellular network provider, so coverage areas for wireless Internet access are more or less the same as they are for cellular phones. There are many different standards for this type of network. Most of them are mobile data standards that previously were used only on cell phones, but are increasingly offered for computing. Some manufacturers offer "mobile broadband" add-ons to their portable computers using the Sprint Broadband Direct, Verizon Broadband Access, and AT&T Broadband Connect networks.
4.0 WLAN standards
Several standards for WLAN hardware exist:
802.11a, b, and g
The 802.11a, b, and g standards are the most common for home wireless access points and large business wireless systems. The differences are:
4.1 802.11a: With data transfer rates up to 54Mbps, it is faster than 802.11b and can support more simultaneous connections. Because it operates in a more regulated frequency, it gets less signal interference from other devices and is considered to be better at maintaining connections. In areas with major radio interference (e.g., airports, business call centers), 802.11a will outperform 802.11b. It has the shortest range of the three standards (generally around 60 to 100 feet), broadcasts in the 5GHz frequency, and is less able to penetrate physical barriers, such as walls
4.2 802.11b: It supports data transfer speeds up to 11Mbps. It's better than 802.11a at penetrating physical barriers, but doesn't support as many simultaneous connections. It has better range than 802.11a (up to 300 feet in ideal circumstances; tests by independent reviewers commonly achieve between 70 and 150 feet), and uses hardware that tends to be less expensive. It's more susceptible to interference, because it operates on the same frequency (2.4GHz) as many cordless phones and other appliances. Therefore, it's not considered a good technology for applications that require absolutely reliable connections, such as live video streaming.
4.3 802.11g: It's faster than 802.11b, supporting data transfer rates up to 54Mbps. It has a slightly shorter range than 802.11b, but still better than 802.11a. Most independent reviews report around 65 to 120 feet in real-world situations. It is backward-compatible with 802.11b products, but will run only at 802.11b speeds when operating with them. It uses the 2.4GHz frequency, so it has the same problems with interference as 802.11b.
4.4 802.11n
The Institute of Electrical and Electronics Engineers (IEEE) has not yet ratified the 802.11.n standard. Because of this, some manufacturers advertise their 802.11n equipment as "draft" devices.
Though specifications may change once the standard is finalized, it is expected to allow data transfer rates up to 600Mbps. Product manufacturers are advertising ranges twice as large as those of as 802.11b/g devices, but as with any wireless devices, range ultimately depends more on the manufacturer and the environment than the standard.
Security standards
The 802.11x standards provide some basic security, but they're becoming less adequate as use of wireless networking spreads. Security standards exist that extend or replace the basic standard:
WEP (Wired Equivalent Privacy)
One of the earliest security schemas, WEP was originally created for 802.11b, but migrated to 802.11a as well. It encrypts data traffic between the wireless access point and the client computer, but doesn't actually secure either end of the transmission. Also, WEP's encryption level is relatively weak (only 40 to 128 bits). Many analysts consider WEP security to be weak and easy to crack.
WPA (Wi-Fi Protected Access)
WPA implements higher security and addresses the flaws in WEP, but is intended to be only an intermediate measure until further 802.11i security measures are developed.
4.5 802.1x
This standard is part of a full WPA security standard. WPA consists of a pair of smaller standards that address different aspects of security:
• TKIP (Temporal Key Integrity Protocol encryption), which encrypts the wireless signal
• 802.1x, which handles the authentication of users to the network
Commonly, wireless systems have you log into individual wireless access points or let you access the wireless network, but then keep you from accessing network data until you provide further authentication (e.g., VPN).
802.1x makes you authenticate to the wireless network itself, not an individual access point, and not to some other level, such as VPN. This boosts security, because unauthorized traffic can be denied right at the wireless access point.
The Wi-Fi Alliance has coined the term "WPA2", for easy use by manufacturers, technicians, and end users. However, the IEEE name of the standard itself is 802.11i. The encryption level is so high that it requires dedicated chips on the hardware to handle it. In practical use; WPA2 devices have interoperability with WPA devices. When not interfacing with older WPA hardware, WPA2 devices will run strictly by the 802.11i specifications.
WPA2 consists of a pair of smaller standards that address different aspects of security:
• WPA2-Personal, which uses a pre-shared key (similar to a single password available to groups of users, instead of a single individual); the pre-shared key is stored on the access point and the end user's computer
• WPA2-Enterprise, which authenticates users against a centralized authentication service
5.0 Future of Wireless LAN Security
Advanced encryption Standard (AES)
Advanced Encryption Standard is gaining acceptance as appropriate replacement for RC4 algorithm in WEP. AES uses the Rijandale Algorithm and supports the following key lengths
128 bit
192 bit
256 bit
AES is considered to be un-crack able by most Cryptographers. NIST has chosen AES for Federal Information Processing Standard (FIPS). In order to improve wireless LAN security the 802.11i is considering inclusion of AES in WEPv2.
Temporal Key Integrity Protocol (TKIP)
The temporal key integrity protocol (TKIP), initially referred to as WEP2, is an interim solution that fixes the key reuse problem of WEP, that is, periodically using the same key to encrypt data. The TKIP process begins with a 128-bit "temporal key" shared among clients and access points. TKIP combines the temporal key with the client's MAC address and then adds a relatively large 16-octet initialization vector to produce the key that will encrypt the data. This procedure ensures that each station uses different key streams to encrypt the data. TKIP also prevents the passive snooping attack by hashing the IV. TKIP uses RC4 to perform the encryption, which is the same as WEP. A major difference from WEP, however, is that TKIP changes temporal keys every 10,000 packets. This provides a dynamic distribution method that significantly enhances the security of the network. An advantage of using TKIP is that companies having existing WEP-based access points and radio NICs can upgrade to TKIP through relatively simple firmware patches. In addition, Weaponry equipment will still interoperate with TKIP-enabled devices using WEP. TKIP is a temporary solution, and most experts believe that stronger encryption is still needed
5.1 802.1X and Extensible Authentication Protocol
Combined with an authentication protocol, such as EAP-TLS, LEAP, or EAP-TTLS, IEEE 802.1X provides port-based access control and mutual authentication between clients and access points via an authentication server. The use of digital certificates makes this process very effective. 802.1X also provides a method for distributing encryption keys dynamically to wireless LAN devices, which solves the key reuse problem found in the current version of
802.11. Initial 802.1X communications begins with an unauthenticated supplicant (i.e., client device) attempting to connect with an authenticator (i.e., 802.11 access point). The access point responds by enabling a port for passing only EAP packets from the client to an authentication server located on the wired side of the access point. The access point blocks all other traffic, such as HTTP, DHCP, and POP3 packets, until the access point can verify the client's identity using an authentication server (e.g., RADIUS). Once authenticated, the access point opens the client's port for other types of traffic.
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.ppt   8_wlans.ppt (Size: 2.06 MB / Downloads: 51)
IEEE 802.11 Wireless Local Area Networks (RF-LANs)
 802.11 WLANs - Outline
 801.11 bands and layers
 Link layer
 Media access layer
 frames and headers
 Physical layer
 frames
 modulation
 Frequency hopping
 Direct sequence
 Infrared
 Implementation
 802.11 WLAN technologies
 IEEE 802.11 standards and rates
 IEEE 802.11 (1997) 1 Mbps and 2 Mbps (2.4 GHz band )
 IEEE 802.11b (1999) 11 Mbps (2.4 GHz band) = Wi-Fi
 IEEE 802.11a (1999) 6, 9, 12, 18, 24, 36, 48, 54 Mbps (5 GHz band)
 IEEE 802.11g (2001 ... 2003) up to 54 Mbps (2.4 GHz) backward compatible to 802.11b
 IEEE 802.11 networks work on license free industrial, science, medicine (ISM) bands:
Other WLAN technologies
 High performance LAN or HiperLAN (ETSI-BRAN EN 300 652) in the 5 GHz ISM
 version 1 up to 24 Mbps
 version 2 up to 54 Mbps
 HiperLAN provides also QoS for data, video, voice and images
 range up to 100 meters only (cable replacement tech.)
 Bluetooth Special Interest Group (SIG)
 Operates at max of 740 kbps at 2.4 GHz ISM band
 Applies fast frequency hopping 1600 hops/second
 Can have serious interference with 802.11 2.4 GHz range network
 Operates at 5 GHz band
 Supports multi-rate 6 Mbps, 9 Mbps,… up to 54 Mbps
 Use Orthogonal Frequency Division Multiplexing (OFDM) with 52 subcarriers, 4 us symbols (0.8 us guard interval)
 Use inverse discrete Fourier transform (IFFT) to combine multi-carrier signals to single time domain symbol
 IEEE 802.11a rates and modulation formats
IEEE 802-series of LAN standards
 802 standards free to
download from
 The IEEE 802.11 and
supporting LAN Standards
 See also IEEE LAN/MAN Standards Committee Web site
IEEE 802.11 Architecture
 IEEE 802.11 defines the physical (PHY), logical link (LLC) and media access control (MAC) layers for a wireless local area network
 802.11 networks can work as
 basic service set (BSS)
 extended service set (ESS)
 BSS can also be used in ad-hoc
 In ESS multiple access points connected by access points and a distribution system as Ethernet
 BSSs partially overlap
 Physically disjoint BSSs
 Physically collocated BSSs (several antennas)
 802.11 Logical architecture
 LLC provides addressing and data link control
MAC provides
 access to wireless medium
 Priority based access (802.12)
 joining the network
 authentication & privacy
 Services
 Station service: Authentication, privacy, MSDU* delivery
 Distributed system: Association** and participates to data distribution
Three physical layers (PHY)
 FHSS: Frequency Hopping Spread
Spectrum (SS)
 DSSS: Direct Sequence SS
 IR: Infrared transmission
 802.11 DSSS
 Supports 1 and 2 Mbps data transport, uses BPSK and QPSK modulation
 Uses 11 chips Barker code for spreading - 10.4 dB processing gain
 Defines 14 overlapping channels, each having 22 MHz channel bandwidth, from 2.401 to 2.483 GHz
 Power limits 1000mW in US, 100mW in EU, 200mW in Japan
 Immune to narrow-band interference, cheaper hardware
 802.11 FHSS
 Supports 1 and 2 Mbps data transport and applies two level - GFSK modulation* (Gaussian Frequency Shift Keying)
 79 channels from 2.402 to 2.480 GHz ( in U.S. and most of EU countries) with 1 MHz channel space
 78 hopping sequences with minimum 6 MHz hopping space, each sequence uses every 79 frequency elements once
 Minimum hopping rate
2.5 hops/second
 Tolerance to multi-path,
narrow band interference,
 Low speed, small range
due to FCC TX power
regulation (10mW)
 How ring-network works
 A node functions as a repeater
 only destination copies
frame to it,
all other nodes
have to discarded
the frame
Unidirectional link
 Token ring
 A ring consists of a single or dual (FDDI) cable in the shape of a loop
 Each station is only connected to each of its two nearest neighbors. Data in the form of packets pass around the ring from one station to another in uni-directional way.
 Advantages :
 (1) Access method supports heavy load without degradation of performance because the medium is not shared.
 (2) Several packets can simultaneous circulate between different pairs of stations.
 Disadvantages:
 (1) Complex management
 (2) Re-initialization of the ring whenever a failure occurs
How bus-network works
 In a bus network, one node’s transmission traverses the entire network and is received and examined by every node. The access method can be :
 (1) Contention scheme : multiple nodes attempt to access bus; only one node succeed at a time (e.g. CSMA/CD in Ethernet)
 (2) Round robin scheme : a token is passed between nodes; node holds the token can use the bus (e.g.Token bus)
 (1) Simple access method
 (2) Easy to add or remove
 (1) Poor efficiency with high
network load
 (2) Relatively insecure, due to
the shared medium
 MAC Techniques - overview
 Contention
 Medium is free for all
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05-04-2011, 04:57 AM

WLAN is a wireless local area network is two or more computers or devices without using cables. Wardrivers can easily break into the wireless network, there is no physical protection of data packets.

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