wireless fidelity full report
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INTRODUCTION

Wi-Fi, or Wireless Fidelity is freedom :it allows you to connect to the internet from your couch at home, in a hotel room or a conferance room at work without wires . Wi-Fi is a wireless technology like a cell phone. Wi-Fi enabled computers send and receive data indoors and out; anywhere within the range of a base station. And the best thing of all, it is fast.
However you only have true freedom to be connected any where 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 able to connect anywhere there are other Wi-Fi CERTIFIED products “ whether you are at home ,office , airports, coffee shops and other public areas equipped with a Wi-Fi access availability.Wi-Fi will be a major face behind hotspots , to a much greater extent.More than 400 airports and hotels in the US are targeted as Wi-Fi hotspots.
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 is a safe buy.
Wi-Fi certification comes from the Wi-Fi Alliance, a non profit international trade organisation that tests 802.11 based wireless equipment to make sure that it meets the Wi-Fi standard and works with all other manufacturerâ„¢s Wi-Fi equipment on the market. The Wi-Fi Alliance (WELA) also has a Wi-Fi certification program for Wi-Fi products that meet interoperability standards. It is an international organisation devoted to certifying interoperability of 802.11 products and to promoting 802.11as the global wireless LAN std across all market segment.
IEEE 802.11 ARCHITECTURES
In IEEE's proposed standard for wireless LANs (IEEE 802.11), there are two different ways to configure a network: ad-hoc and infrastructure. In the ad-hoc network, computers are brought together to form a network "on the fly." As shown in Figure 1, there is no structure to the network; there are no fixed points; and usually every node is able to communicate with every other node. A good example of this is the aforementioned meeting where employees bring laptop computers together to communicate and share design or financial information. Although it seems that order would be difficult to maintain in this type of network, algorithms such as the spokesman election algorithm (SEA) [4] have been designed to "elect" one machine as the base station (master) of the network with the others being slaves. Another algorithm in ad-hoc network architectures uses a broadcast and flooding method to all other nodes to establish who's who.


Figure 1a: The ad-hoc network structure in the 802.11 protocol.
The ad-hoc network (Figure 1a) is one formed from a collection of peer nodes all using RF links. This network has no formal structure; all nodes can communicate with all other nodes. Several algorithms are available to prevent this from being total chaos, however, including a spokesman election algorithm that selects a master from the collective and makes all others slaves. Another possibility is to use broadcast and flooding to all other nodes to establish an addressing scheme. A good example of an ad-hoc network is one that is formed when a group gets together at a meeting and everyone has WLAN-enabled PCs. They can form an ad-hoc network at the meeting to share data.
As shown in figure 2 the network structure used in wireless LANs is the infrastructure. This architecture uses fixed network access points with which mobile nodes can communicate. These network access points are sometime connected to landlines to widen the LAN's capability by bridging wireless nodes to other wired nodes. If service areas overlap, handoffs can occur. This structure is very similar to the present day cellular networks around the world.

They can form an ad-hoc network at the meeting to share data.


Figure 1b: The infrastructure network structure in the 802.11 protocol.
The infrastructure network has a formal structure (Figure 1b). It uses fixed access points (AP), which are RF-enabled nodes on a hard-wired LAN. The structure allows mobile nodes to communicate with the access points to join the network. Mobile units can move freely within the area covered by the access point radios, typically a range of 100 meters for the 2.4 GHz band. The RF link is intended to operate with units moving at pedestrian or vehicular speeds.
The ABCs of IEEE 802.11
At the beginning the IEEE802.11 was an extension technology for conventional or wired LANs.Nowadays it has grown in to something much more capable, complex and confusing. With growth, new issues have arisen such as security, roaming among multiple access points, and even quality of services. These issues are dealt by extensions to the standard identified by the letters of the alphabet derived from the 802.11 task groups that created them:
802.11a

The 802.11a supplement to 802.11 was published in 1999. It uses Orthogonal Frequency Division Multiplexing (OFDM) to provide data rates to 54 Mbps in the 5 GHz U-NII licensed National Information Infrastructure)
802.11b
Commercially trade marked in 1999 by Wireless Ethernet Compatibility Alliance (WECA)as Wi-Fi , this is the extension that made 802.11a a house hold world
802.11g
The 802.11g task group is working on a supplement to the 802.11 standard that defines a technology for operation at 2.4 GHz that offers higher data rates (up to 22 Mbps) using OFDM, while remaining backwards compatible to 802.11b.


BASIC COMPONENTS
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 APs
A wireless AP is a wireless network node that acts as a bridge between STAs and a wired network. A wireless AP contains:
o At least one interface that connects the wireless AP to an existing wired network (such as an Ethernet backbone).
o A wireless network device with which it creates wireless connections with STAs.
o 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 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 an 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.

TECHNOLOLGY
Wi-Fi uses radio technology called IEEE 802.11b to provide secure ,reliable,fast wireless connectivity.A Wi-Fi network can be used to connect computers to each other, to the internet and to the wired networks.
Though WLANs are easy to deploy, the network administrator or IT professional will benefit from some basic knowledge about radio wave propagation. Although it is possible to utilize infrared technology (which always requires line of sight between elements of the network), this paper deals only with Radio Frequency (RF) wireless networks, which have become the industry accepted standard for WLANs.

The reason for using RF is simple. It can pass through solid objects such as office walls. However, radio waves do not go on forever in all directions without weakening or being affected by physical barriers. The user needs to have some understanding of their propagation characteristics, as well as the relationship between power levels and data rates, before a wireless network can be designed.


Propagation Characteristics Must Be Considered

Reflection - Radio waves can be reflected by some materials. This phenomenon is often used to steer microwave signals between stations that are not line-of-sight, but in an office environment it can create multipath (see below).

Absorption - Radio waves can be absorbed by many materials such as water, plastic, sheetrock, and carpet.

Geometric Spreading loss - Radio waves, like light waves, get weaker as they expand outward away from their source. This loss grows as the square of the distance. This means that if a device is moved twice as far away, the signal power drops by one fourth.

Path loss - The above phenomena lead to path loss, or an unavoidable weakening of the signal's power as it propagates outward. In an office environment, the placement of furniture and walls, and even the movement and location of people, will contribute to the amount of path loss.

Multipath - If a received signal is made up of radio waves from the same signal that has dispersed and arrived from different paths, i.e. some of the original energy was often exhibit this as ghosting. Network users may likewise experience its digital counterpart - referred to as intersymbol interference. This is caused when the difference in time between radio waves arriving from the same signal, referred to as delay spread, is enough to cause symbol overlap in the digital data. As the data transmission speed gets faster, the time between received data bits get smaller and more susceptible to intersymbol interference, so multipath places an upper limit on data transmission speed.

Propagation characteristics are frequency dependent:
At lower frequencies (longer wavelengths), less RF energy is absorbed by obstructions. Signals can pass through solid objects (walls) more readily.

At higher frequencies (shorter wavelengths), smaller antennas can be used. However, if antennas are scaled down proportionately with wavelength, the received signal power will decrease as a function of frequency squared, due to less signal energy being intercepted by the smaller antenna. This shortcoming can be overcome by using higher gain antennas.
How the properties of radio waves affect networking capabilities
When used in wireless technologies, the ideal radio wave should have high speed, use little energy and travel far distaces.This type of radio wave would let us transfer information in few milliseconds, require little battery power and send signals at whatever range we needed.
In reality however, it is impossible to achieve all three of these characteristics at the same time. It is established fact that the further and faster that a radio wave travels, the more energy it needs.
Because it is impossible to simultaneously achieve high speed, low power consumption and long range in radiowave, product designers and developers have instead selected specific characteristics to optimize in certain conditions while creating wireless technologies. This approach has led to the concepts of wireless area networks of different magnitudes, (ie., personal ,local metropolitan, global, etc.) Each type of wireless area network signifies a specific combination of radio characteristics that in turn translate into specific applications and usage scenarios.
For example, while developing applications for a wireless personal area network (WPAN), the wireless area network with the shortest range , product designers and developers need to consider what scenarios demand low power more than they do high speed or great range. Conversely, while developing uses for the wireless local area network (WLAN), product designers and developers must determine in which situations users would value moderate range and moderate speed more than they would low power consumption.

Similarly, the energy levels demanded by Wi-Fi render it impractical for small battery “powered devices like mobile phones, personal gadgets , and most PDAs. For example, typical Wi-Fi compact Flash and PC cards use 110-140 mA during idle mode and 200-300 mA during transmission, each atleast twice the amount of power required by Bluetooth cards. As a result, most manufacturers today are implementing Wi-Fi into notebook and desktop computers and serves, whose power resources are better suited for high power requirements of Wi-Fi.

SECURITY
Putting Wi-Fi Security in Perspective

Before this issue is explained in detail, the reader needs to keep in mind that Wi-Fi (IEEE 802.11) only attempts to provide security for the wireless portion of a network. It is not end-to-end security, and it was never intended to do more than prevent casual eavesdropping, which is what un-encrypted wired Local Area Networks (LANs) provide.

The user must, however, keep in mind that wireless networks cannot provide the same level of inherent security at the physical level that wired networks do. Radio waves pass through walls and can be intercepted from a distance. Even though a standard Wireless LAN (WLAN) card in a laptop may indicate a marginal or even non-existent signal, specialized equipment may be able to receive the signal from a much greater distance. More security is often required, whether the network is wired or wireless.

There are many components to effective network security, including the following:
Authentication - assurance that a packet comes from where it claims
Confidentiality - protection from disclosure to unauthorized persons
Access control - keeping unauthorized users out
Integrity - ensuring that data is error-free
Network security is generally implemented in layers, utilizing all of the above components and built around the seven-layer OSI Reference Model . Unlike the common saying "strong as the weakest link," layered network security is just the opposite. It is as strong as its strongest link. For example, end-to-end security can be achieved by a strong mechanism in the application layer only, even if link-layer security is broken or non-existent. However, that solution only provides security for that particular application. The advantage to applying security at progressively lower levels is that it becomes generally available to more applications.

Also, remember that corporate Wi-Fi usually attached to a wired LAN. So even if 802.11 link-level security was very strong, it only applies to the wireless portion of the network. Higher-level layers of security may still need to be employed, even if a firewall is utilized for the wired portion.

Wi-Fi Security Options

IEEE 802.11 contains an encryption option intended to provide confidentiality. The Wired Equivalent Privacy (WEP) option is defined in the 802.11 standard as "protecting authorized users of a Wi-Fi from casual eavesdropping." Recently, this security scheme has come under a great deal of criticism, accompanied by a number of papers which uncover weaknesses and outline how WEP can be defeated. Additionally, tools to exploit these weaknesses are now freely available over the Internet.

The Problem with WEP

WEP utilizes 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 ciphertext (the encrypted data), and at the other end to decrypt it - convert the ciphertext 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. However, care must be taken to ensure that the application is well suited for the proper implementation of a stream cipher, or for that matter, whatever encryption algorithm is being used.
Proper Use of Stream Ciphers

Stream ciphers are very simple and operate in theory by expanding the shared key into an infinite pseudo-random key stream which is logically combined (XORed) with the plaintext to produce ciphertext. Being a symmetric cipher, the user employs the shared key at the receiving end to regenerate the identical key stream, which is then XORed with the ciphertext to reproduce the plaintext. In practice, of course, an infinite key stream is never produced; it is only as long as the data stream being encrypted.

Once a key has been used to generate a key stream, the same key can never be reused again because it will generate the same key stream. If an attacker can obtain two different ciphertexts encrypted with the same key stream, the encryption process can be broken and the contents of the shared key determined. An important consequence of this is that if an encrypted transmission is interrupted and the encryption and decryption algorithms lose synchronization, and there is no means to resynchronize the process, then the entire message must be resent again, but with a different key.

The RC4 stream cipher has no mechanism to resynchronize the encryption process if an interruption occurs. Thus, it is not well-suited to applications where there is a possibility of a transmission being interrupted, unless provision is made to restart the session with a new key. For example, the RC4 stream cipher is successfully used to provide encryption for Secure Socket Layer (SSL) services for Internet transactions. An SSL session typically lasts a relatively short period of time and operates over a reliable channel where it is unlikely that a packet will be dropped. If it is, the session is started over, but with a different key. The new key is exchanged during a secure authentication process (using RSA public key cryptography) before the encrypted transaction is begun.

Improper Use of a Stream Cipher by WEP

The problem arises when the RC4 stream cipher is being used to encrypt data being sent over a channel, such as a wireless link, where it is highly likely that packets will be dropped. If there is no provision for key management (802.11 currently has none), then there is no way to create and exchange a new key with an authenticated user so that a packet can be resent.

The designers of WEP tried to get around this by appending a unique key. The effect is that instead of having only one 40-bit shared key available for use, there are now 224 different 64-bit shared keys. The receiver only needs to know the secret shared 40-bit portion which is common to all of them. The unique 24-bit IV vector, which is transmitted unencrypted with each packet, determines which of the keys was used to encrypt a particular packet. The key stream is generated with this unique 64-bit "packet" key and the packet key and the key stream change for every packet.

One of the problems with this scheme is that there are only a finite number of IVs available for use, and there is no mechanism in place for changing the shared key when all of the available unique IVs get used up. Another is that the simple process of concatenating the IV onto the shared key produces unique keys that are too similar.
These fundamental weaknesses proved to be WEP's initial undoing.
So¦ WEP is now generally considered to do no more than "discourage casual eavesdropping," which is all it was ever intended to do..
Providing Additional Security

Virtual Private Networks (VPNs)
It provide the most robust security solutions for corporate LANs and are already widely used for intranets and remote access. A VPN typically utilizes a dedicated server that provides both authentication and confidentiality. Wireless Access Points are also beginning to include VPN technologies within their devices, allowing simplified VPN deployment.A VPN works through the VPN server at the company head quarters, creating an encryption scheme for data transferred to computers outside the corporate offices.The special VPN software on the remote computer uses the same encryption scheme, enabling the data to be safely transferred back and forth with no chance of interception.
The following steps to insure that wireless networks are secure:
For home users and small offices:
¢ Use all of the 802.11 security options, including WEP.
¢ Use any other security features specific to your vendor's products.
¢ Change default passwords.
¢ Don't use the default key. Change it immediately and then repeatedly on a regular basis.
Additional steps for corporate users:
¢ Install the WLAN outside the firewall.
¢ Use a VPN with a physical authentication token such as a SmartCard or SecureID card.
SPECIAL FEATURES OF Wi-Fi
Unlike todayâ„¢s wired network, a Wi-Fi network requires little more than an access point(AP). Access to a Wi-Fi- network does not require an expensive connection to each user. Wi-Fi technology is also far less expensive to deploy than the limited wireless technologies of currently existing cellular servicing providers.
Access to a Wi-Fi broad band can be provided both outdoors and indoors. Whether from an outdoor café or a park bench a person can access the Internet if they are in range of a service station. Such a Wi-Fi broadband is much power full and can transmit data at a rate of 11Mbps which is sufficient for all types of multimedia.
Many schools and businesses have unsuitable building layouts or walls that cannot be wired for various reasons making it difficult or impossible to build a wired network. Wi-Fi is a very cost effective alternative in these environments.
A Wi-Fi network can provide many benefits for the society. It can provide local hospitals.
Though the radio waves are of relatively high frequency, they are not powerful enough to pass through multiple layers of building materials. Specifically radio waves are completely blocked by steel. For this reasons the factors deciding performance are proximity to access point and the degree to which the signal is blocked by the surroundings.
As more computers begin to communicate with the same access point ,a bottleneck occurs. An access point has a finite amount of network bandwidth to

which it is physically linked. As a result, all computers that are associated with a specific access point must share the same bandwidth. More computers means the possibility for a slower network connection.
Since Wi-Fi technology is constantly improving these shortcomings will get removed soon.


CONCLUSION
Wi-Fi provides freedom: freedom to physically move around your home or business and still stay connected to the internet or local network; freedom to grow and move an office or business without having to install new cables and wires, freedom to be connected while travelling and on the road .Wireless ˜hotspots™(airports, hotels, coffee shops, convention centers and any other place where someone can connect to a wireless network ) are being installed world while . all this means Wi-Fi truly does provide un precedented freedom .plus ,it is cool and fun “as those in the know say ˜once you go wire less , you will never want to use a cable again .™
There are real and measurable benefits to using a wireless network Vs a standard wired network. For a home installation customer, the greatest benefit is that there are no wires needed: you donâ„¢t need to drill holes in walls and floors; you donâ„¢t need to drag cables across rooms or hide them under rugs. One Wi-Fi access point can provide network access for any typically sized home . And if you live in a rental or a historical building, you may not be allowed to drill holes- that makes wireless your only solution.
Wi-Fi use is growing fast in homes, public access areas and business “both large and small. The Wi-Fi alliance is active with many industry organisations and is working closely with manufacturers to make sure that existing Wi-Fi gear is compatable with wireless technologies developed in the future .

REFERENCES
1. Books on Wireless LAN technologies
2. Articles on Wi-Fi from the Wi-Fi alliance group of companies.
3. Articles in magazines such as electronics for you.
4. Paper on Wi-Fi security from the Wi-Fi alliance.
5. ieeespectrum.com




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.It refers to wireless LAN products based on the IEEE 802.11b specification.Users can share documents and project and implimentations,as well as an internet connection among various computer stations.
A Wi-Fi network operates just like a wired network, without restrictions imposed by wires .Not only does it enable users to move around and be mobile at home and at work, it also provides easy connections to the internet and business networks while travelling.
The technologies used in this field are one of the best in the wireless space. When compared with other fast improving technologies like Bluetooth and 3G, Wi-Fi is seen to have many advantages. We can setup networks at home and office using Wi-Fi . It is fairly easy to setup a Wi-Fi enabled network at home or a small office. Wi- Fi is several times faster than Bluetooth and operates like a high speed modem.
There are many security issues that come under Wi-Fi . The main problem that it has till now is that it is easy for hackers to attack the network. The security method that is used now is the WEP (Wired Equivalent Privacy).The new VPN (Virtual Private Network) method seems to correct everything that is wrong with WEP.

ACKNOWLEDGEMENT
I extend my sincere thanks to Prof. P.V.Abdul Hameed, Head of the Department for providing me with the guidance and facilities for the Seminar.
I express my sincere gratitude to Seminar coordinator Mr. Berly C.J, Staff in charge, for their cooperation and guidance for preparing and presenting this seminar and presentation.
I also extend my sincere thanks to all other faculty members of Electronics and Communication Department and my friends for their support and encouragement.
ARIFA HAMEED

CONTENTS
1. INTRODUCTION 01
2. IEEE 802.11 ARCHITECTURES 02
3. BASIC COMPONENTS 06
4. OPERATION BASICS 08
5. TECHNOLOLGY 09
6. SECURITY 13
7. SPECIAL FEATURES OF Wi-Fi 18
8. CONCLUSION 20
9. REFERENCES 21
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PAPER PRESENTATION

PRESENTED BY
M.Girish kumar
G.prakash
IIIECE
St.Ann's College of Engineering &Technology
CHIRALA

ABSTRACT
Technology is no longer judged by its technical brilliance, but by the return on investment (both tangible and intangible). This in turn, is dictated by the killer application for that technology. Wi reless Networks fit into this because the technology has been around long enough and can provide enough benefits to be seriously considered for deployment.
At the enterprise, it provides communication support for mobile computing. It overcomes and, in fact, annihilates the physical limitation of wired networks in terms of adaptability to a variation in demand. Network connectivity in a company's meeting room is a classic example. The number of users using that room would vary for different meetings. So, it would be difficult to decide how many wired network ports to put there. With wireless access, the number of users is mostly constrained by the bandwidth available on the wireless network.
Mobility is another feature by wireless. Mobile users can be truly m obile, in that hey don't need to be bound to their seats when connecting to the network. Mobility, however is not only associated with users, it's also associated with the infrastructure itself. You can have a wireless network up and running in no time, a boon for people who need to do it for exhibitions, events, etc.
This leads to other provision of wireless, that of scalability. It really helps in extending your network. It also becomes important if an enterprise has a rented office and needs to shift to a new place. At home, the need for wireless is more to do with ubiquitous computing.
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 a conference room at work without wires. It is a wireless technology like cell phones, Wi -Fi enabled computers send and receive data indoors and outdoors; anywhere within the range of the base station. And the best thing of all, Wi-Fi is fast. In fact, it's several times faster than the fastes t cable modem connection.
Wireless technology, therefore is really happening, and should be seriously considered. The following presentation explains wireless LANs, their basic operations, topologies; security features and answers some of the questions eva luating WLAN technology.
1. IEEE 802.11b Wireless Networking Overview
Approval of the IEEE 802.11 standard for wireless local area networking (WLAN) and rapid progress made toward higher data rates have put the promise of truly mobile computing within reach. While wired LANs have been a mainstream technology for at least fifteen years, WLANs are uncharted territory for most networking professionals.
In September of 1999, the Institute of Electrical and Electronic Engineers (IEEE) ratified the specification for IEEE 802.11b, also known as Wi -Fi. IEEE 802.11b defines the physical layer and media access control (MAC) sub layer 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 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 currentl y 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.
2. Wireless Networking Components
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 AP: wireless AP is a wireless network node that acts as a bridge between STAs and a wired network. A wireless AP contains:
1. At least one interface that connects the wireless AP to an existing wired network (such as an Ethernet backbone).
2. A wireless network device with which it creates wireless connections with
STAs.
3. 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 wire less 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.
3. IEEE 802.11b Operating Modes (network topology)
AP's are not mobile, and form part of the wired network infrastructure. A BSS in this Configuration is said to be operating in infrastructure mode.
IEEE 802.11 defines two operating modes: Ad hoc mode and Infrastructure mode. The basic topology of an 802.11 network is shown in Figure 1. A Basic Service Set (BSS) consists of two or more wireless nodes, or stations (STAs), which have r ecognized each other and have established communications. In the most basic form, stations communicate directly with each other on a peer-to-peer level sharing a given cell coverage area. This type of network is often formed on a temporary basis, and is commonly referred to as an ad hoc network, or Independent Basic Service Set (IBSS).
The Extended Service Set (ESS) shown in Figure 2 consists of a series of overlapping BSSs (each containing an AP) connected together by means of a Distribution System (DS). Although the DS could be any type of network, it is almost invariably an Ethernet LAN. Mobile nodes can roam between APs and seamless campus -wide coverage is possible.
4. IEEE 802.11b 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 suc h 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.
5. Radio Technology in 802.11
IEEE 802.11 provides for two variations of the PHY. These include two (2) RF technologies namely Direct Sequence Spread Spectrum (DSSS), and Freque ncy Hopped Spread Spectrum (FHSS). The DSSS and FHSS PHY options were designed specifically to conform to FCC regulations (FCC 15.247) for operation in the 2.4 GHz ISM band, which has worldwide allocation for unlicensed operation.
| Data
1 1 Bit Barker Cod** (PRN); 101 1101000
Figure 3 Digital Modulation of Data with PRM Sequence
DSSS systems use technology similar to GPS satellites and some types of cell phones. Each information bit is combined via an XOR function with a longer Pseudo -random Numerical (PN) sequence as shown in Figure 3. The result is a high speed digital stream which is then modulated onto a carrier frequency using Differential Phase Shift
Keying (DPSK).
When receiving the DSSS signal, a matched filter correlator is used as shown in Figure 4.The correlator removes the PN sequence and recovers the original data str eam. Tat the higher data rates of 5.5 and 11 Mbps, DSSS receivers employ different PN codes and a bank of correlators to recover the transmitted data stream. The high rate modulation method is called Complimentary Code Keying (CCK). The effects of using PN codes to generate the spread spectrum signal are shown in Figure 5.
As shown in Figure 5a, the PN sequence spreads the transmitted bandwidth of the resulting signal (thus the term, "spread spectrum") and reduces peak power. Note however, that total power is unchanged. Upon reception, the signal is correlated with the same PN sequence to reject narrow band interference and recover the original binary data (Fig. 5b). Regardless of whether the data rate is 1, 2, 5.5, or 11 Mbps, the channel bandwidth is about 20 MHz for DSSS systems. Therefore, the ISM band will accommodate up to three non-overlapping channels
6. Multiple Access
The basic access method for 802.11 is the Distributed Coordination Function (DCF) which uses Carrier Sense Multiple Access / Collision Avoidance (CSMA / CA). This requires each station to listen for other users. If the channel is idle, the station may transmit. However if it is busy, each station waits until transmission stops, and then enters into a random back off procedure. This prevents multiple stations from seizing the medium immediately after completion of the preceding transmission.
Figure 7 CSMA/CD Back-off Algorithm
Packet reception in DCF requires acknowledgement as shown in Figure 7. The period between completion of packet transmission and start of t he ACK frame is one Short Inter Frame Space (SIFS). ACK frames have a higher priority than other traffic. Fast acknowledgement is one of the salient features of the 802.11 standard, because it requires ACKs to be handled at the MAC sub layer.
The underlying assumption is that every station can "hear" all other stations. This is not always the case. Referring to Figure 8, the AP is within range of the STA -A, but STA-B is out of range. STA-B would not be able to detect transmissions from STA -A, and the probability of collision is greatly increased. This is known as the Hidden Node.
To combat this problem, a second carrier sense mechanism is available. Virtual Carrier Sense enables a station to reserve the medium for a specified period of time through the use of RTS/CTS frames.
7. IEEE 802.11 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 Equi valent Privacy (WEP)
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 cli ent 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 th at 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 dist ributed manually, this method of authentication does not scale to a large infrastructure mode network (for example, corporate campuses and public plac es, such as malls and airports) for use.
Inherent in the nature of wireless networks, securing physical ac cess 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. 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.
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
8. The Wireless Ethernet Compatibility Alliance
The recently adopted Complimentary Code Keying (CCK) waveform delivers speeds of 5.5 and 11 Mbps in the same occupied bandwidth as current generation 1 and 2 Mbps DSSS radios and will be fully backward compatible. Now that a standard is firmly in place, WLANs will become a part of the enterprise networking landscape within the next twelve months.
The mission of the Wireless Ethernet Compatibility Alliance is to provide certification of compliance with the IEEE 802.11 Standard and to ensure that products from multiple vendors meet strict requirements for interoperability. With cross vendor interoperability assured, WLANs are now able to fulfill the promise of hi gh speed mobile computing.
Conclusion:
The use of wireless LANs is expected to increase dramatically in the future as businesses discover the enhanced productivity and the increased mobility that wireless communications can provide in a society that is m oving towards more connectionless connections.
In conclusion, the panelists felt that hurdles in deploying WLANs can be overcome. Cost of wireless services are already falling. The issue is now to lower the costs of the device that is needed to access the WLAN. Large chop design companies can make use of this opportunity to get into the market place. And Wi -Fi cannot move ahead quickly without support form private and government sectors
Bibliography:
1. Data over wireless networks -Gilbert Held
2. Electronics for you (magazine) June 2003 & February 2003
3. Electronics today (magazine) March 2003
4. A Technical tutorial on the IEEE 802.11 protocol - Pablo Brenner
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Wireless LAN Security 802.11b and Corporate Networks



Introduction
Although a variety of wireless network technologies have or will soon reach the general business
market, wireless LANs based on the 802.11 standard are the most likely candidate to become
widely prevalent in corporate environments. Current 802.11b products operate at 2.4GHz, and
deliver up to 11Mbps of bandwidth – comparable to a standard Ethernet wired LAN in
performance. An upcoming version called 802.11a moves to a higher frequency range, and
promises significantly faster speeds. It is expected to have security concerns similar to 802.11b.
This low cost, combined with strong performance and ease of deployment, mean that many
departments and individuals already use 802.11b, at home or at work – even if IT staff and
security management administrators do not yet recognize wireless LANs as an approved
technology. This paper addresses the security concerns raised by both current and upcoming
802.11 network technologies.
Wireless LAN Business Drivers
Without doubt, wireless LANs have a high gee-whiz factor. They provide always-on network
connectivity, but don’t require a network cable. Office workers can roam from meeting to meeting
throughout a building, constantly connected to the same network resources enjoyed by wired,
desk-bound coworkers. Home or remote workers can set up networks without worrying about how
to run wires through houses that never were designed to support network infrastructure.
Wireless LANS may actually prove less expensive to support than traditional networks for
employees that need to connect to corporate resources in multiple office locations. Large hotel
chains, airlines, convention centers, Internet cafes, etc., see wireless LANs as an additional
revenue opportunity for providing Internet connectivity to their customers. Wireless is a more
affordable and logistically acceptable alternative to wired LANs for these organizations. For
example, an airline can provide for-fee wireless network access for travelers in frequent flyer
lounges – or anywhere else in the airport.
Market maturity and technology advances will lower the cost and accelerate widespread adoption
of wireless LANs. End-user spending, the primary cost metric, will drop from about $250 in 2001
to around $180 in 2004 (Gartner Group). By 2005, 50 percent of Fortune 1000 companies will
have extensively deployed wireless LAN technology based on evolved 802.11 standards (0.7
probability). By 2010, the majority of Fortune 2000 companies will have deployed wireless LANs
to support standard, wired network technology LANs (0.6 probability).
Reality Check
For the foreseeable future wireless technology will complement wired connectivity in enterprise
environments. Even new buildings will continue to incorporate wired LANs. The primary reason is
that wired networking remains less expensive than wireless. In addition, wired networks offer
greater bandwidth, allowing for future applications beyond the capabilities of today’s wireless
systems.
Although it may cost 10 times more to retrofit a building for wired networking (initial construction
being by far the preferred time to set up network infrastructure), wiring is only a very small fraction
of the cost of the overall capital outlay for an enterprise network. For that reason, many
corporations are only just testing wireless technology. This limited acceptance at the corporate
level means few access points with a limited number of users in real world production
environments, or evaluation test beds sequestered in a lab. In response, business units and
individuals will deploy wireless access points on their own. These unauthorized networks almost
certainly lack adequate attention to information security, and present a serious concern for
protecting online business assets.
Finally, the 802.11b standard shares unlicensed frequencies with other devices, including
Bluetooth wireless personal area networks (PANs), cordless phones, and baby monitors. These
technologies can, and do, interfere with each other. 802.11b also fails to delineate roaming(moving from one cell to another), leaving each vendor to implement a different solution. Future
proposals in 802.11 promise to address these shortcomings, but no shipping products are on the
immediate horizon
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Wireless Fidelity
What is the goal of 802.11 standard ?

 To develop a Medium Access Control (MAC) and Physical Layer (PHY) specification for wireless connectivity for fixed, portable and moving stations within a local area.
802.11 sub-standards(amendments ) ….
 802.11 MAC (Media Access Control) ratified 1999
 802.11b PHY 2.4 GHz (max 11 Mbps) ratified 1999
 802.11a PHY 5.0 GHz (max 54 Mbps) ratified 1999
 802.11g PHY 2.0 GHz (max 54 Mbps) ratified 2003
 802.11i Security draft number XXX
 802.11e QoS, Multimedia draft number XXX
 802.11h European regulations for 5GHz draft number XXX
 802.11h Japan regulations for 5GHz draft number XXX
Do I need any license to use 802.11 device ?
 No , 2.4 GHz and 5.0 GHz are public available frequency !!!
Context with OSI layers
Logical Link Control Services
Standard 802.11 frame format
Frames types and subtypes

 Three types of frames:
 Control
(ACK,RTS,CTS ,Power Save …)
 Management
(Beacon,Probe Request ,Probe Response,
Association request , Association response …)
 Data
(Data, Null Data, Data_CF_Ack , ….)
Infrastructure Model includes: (most common)
• Stations (STA)
– any wireless device
• Access Point (AP)
– connects BSS to DS
– controls access by STA’s
• Basic Service Set (BSS)
– a region controlled by an AP
– mobility is supported within a single BSS
• Extended Service Set (ESS)
– a set of BSS’s forming a virtual BSS
– mobility is supported between BSS’s in an ESS
• Distribution Service (DS) connection between BSS’s
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