Home | | Mobile and Pervasive Computing | Wi-Fi-Wireless Fidelity

Chapter: Mobile Networks : Wireless Networks

Wi-Fi-Wireless Fidelity

Wireless Fidelity is commonly known as Wi-Fi, developed on IEEE 802.11 standards, is commonly used technology development in wireless communication.



Wireless Fidelity is commonly known as Wi-Fi, developed on IEEE 802.11 standards, is commonly used technology development in wireless communication. As the names indicate, WI-FI provides wireless access to applications and data across a radio network. WI-FI sets up many ways to build up a connection between the transmitter and the receiver such as DSSS, FHSS, IRInfrared and OFDM.


Wi-Fi provide its users with the authorization of connecting to the Internet from any place such as their home, office or a public place without the hassles of plugging in the wires. Wi-Fi is faster than the conventional modem for accessing information over a huge network. With the help of different amplifiers, the users can easily alter their location without interference in their network access. Wi-Fi devices are yielding with each other to grant well-organized access of information to the user. Wi-Fi location, the users can attach to the wireless network is called a Wi-Fi hotspot. Through the Wi-Fi hotspot, the user can evenimprove their home business as accessing information through Wi-Fi is easy Accessing a wireless network through a hotspot in some cases is free of cost while in some it may carry extra charges. Many set of Wi-Fi devices such as PCI, miniPCI, USB, Cardbus and PC card, ExpressCard make the Wi-Fi experience suitable and enjoyable for the users. Distance from a wireless network can decrease the signal strength to quite an extent; some devices such as Ermanno Pietrosemoli and EsLaRed of Venezuela Distance are used for amplifying the signal power of the network. These devices create embedded systems that communicate with any other node on the Internet.


Wi-Fi uses radio networks to broadcast data between its nodes. Such networks are made up of cells that grant coverage across the network. The further the number of cells, the larger and stronger is the coverage on the radio network. The radio technology is a absolute package deal as it offers a secure and reliable connectivity. Radio bands such as 2.4GHz and 5GHz depend on wireless hardware such Ethernet protocol and CSMA. Originally, Phase Shift Keying (PSK), a modulation method for transmission of data was used, but now it has been replaced with CCK. Wi-Fi uses many spectrum such as FHSS and DSSS. The most accepted Wi-Fi technology such as 802.11b operates on the range of 2.40 GHz up to 2.4835 GHz band. This provides a complete platform for operating Bluetooth strategy, cellular phones, and other scientific equipments. While 802.11a technology has the range of 5.725 GHz to 5.850 GHz and provides up to 54 Mbps in speed. 802.11g technology is even enhanced as it cover three non-overlapping channels and permit PBCC. 802.11e technology takes a pale lead by providing outstanding streaming quality of video, audio, voice channels etc.

Wi-Fi communication devices are extended forms of radios used for cell phones and walkie-talkies: they simultaneously transmit and receive radio waves and convert 1s to 0s into the radio waves along with reconverting the radio waves into 1s and 0s, however the Wi-Fi radios enjoy some exceptional features.




Wi-Fi allows cheaper deployment of local area networks (LANs). Also spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.


Manufacturers are building wireless network adapters into most laptops. The price of chipsets for Wi -Fi continues to drop, making it an economical networking option included in even more devices.


Different competitive brands of access points and client network-interfaces can inter-operate at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backwards compatible. Unlike mobile phones, any standard Wi-Fi device will work anywhere in the world.


Wi-Fi Protected Access encryption (WPA2) is considered secure, provided a strong passphrase is used. New protocols for quality-of-service (WMM) make Wi-Fi more suitable for latency-sensitive applications (such as voice and video). Power saving mechanisms (WMM Power Save) extend battery life.




Spectrum assignments and operational limitations are not consistent worldwide: most of Europe allows for an additional two channels beyond those permitted in the US for the 2.4 GHz band (1–13 vs. 1–11), while Japan has one more on top of that (1–14). As of 2007, Europe is essentially homogeneous in this respect.


A Wi-Fi signal occupies five channels in the 2.4 GHz band. Any two channel numbers that differ by five or more, such as 2 and 7, do not overlap. The oft-repeated adage that channels 1, 6, and 11 are the only non-overlapping channels is, therefore, not accurate. Channels 1, 6, and 11 are the only group of three non-overlapping channels in the U.S. In Europe and Japan using Channels 1, 5, 9, and 13 for 802.11g and 802.11n is recommended.

Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (100 mW).  The current 'fastest' norm, 802.11n, uses double the radio spectrum/bandwidth (40 MHz) compared to 802.11a or 802.11g (20 MHz). This means there can be only one 802.11n network on the 2.4 GHz band at a given location, without interference to/from other WLAN traffic. 802.11n can also be set to use 20 MHz bandwidth only to prevent interference in dense community.




2.  Distribution and integration

3.  Association, re-association, and disassociation

4.  Authentication and deauthentication


5.  Providing privacy



This service is used by mobile stations in an infrastructure network every time they send data. Once a frame has been accepted by an access point, it uses the distribution service to deliver the frame to its destination. Any communication that uses an access point travels through the distribution service, including communications between two mobile stations associated with the same access point.




Integration is a service provided by the distribution system; it allows the connection of the distribution system to a non-IEEE 802.11 network. The integration function is specific to the distribution system used and therefore is not specified by 802.11, except in terms of the services it must offer.




Delivery of frames to mobile stations is made possible because mobile stations register, or associate, with access points. The distribution system can then use the registration information to determine which access point to use for any mobile station.




When a mobile station moves between basic service areas within a single extended service area, it must evaluate signal strength and perhaps switch the access point with which it is associated. Reassociations are initiated by mobile stations when signal conditions indicate that a different association would be beneficial; they are never initiated by the access point. After the reassociation is complete, the distribution system updates its location records to reflect the reachability of the mobile station through a different access point.




To terminate an existing association, stations may use the disassociation service. When stations invoke the disassociation service, any mobility data stored in the distribution system is removed. Once disassociation is complete, it is as if the station is no longer attached to the network. Disassociation is a polite task to do during the station shutdown process. The MAC is, however, designed to accommodate stations that leave the network without formally disassociating.



Physical security is a major component of a wired LAN security solution.


Wired network‘s equipment can be locked inside offices. Wireless networks cannot offer the same level of physical security, however, and therefore must depend on additional authentication routines to ensure that users accessing the network are authorized to do so. Authentication is a necessary prerequisite to association because only authenticated users are authorized to use the network. (In practice, though, many access points are configured for "open-system" mode and will authenticate any station.)


Deauthentication terminates an authenticated relationship. Because authentication is needed before network use is authorized, a side effect of deauthentication is termination of any current association.




WiFi hotspots can be open or secure. If a hotspot is open, then anyone with a WiFi card can access the hotspot. If it is secure, then the user needs to know a WEP key to connect. WEP stands for Wired Equivalent Privacy. WEP is an encryption system for the data that 802.11 sends through the air. Encryption system prevents any non-authorized party from reading or changing data. Specifically, it is the process of encoding bit stream in such a way that only the person (or computer) with the key (a digital sequence) can decode it.


Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail
Mobile Networks : Wireless Networks : Wi-Fi-Wireless Fidelity |

Privacy Policy, Terms and Conditions, DMCA Policy and Compliant

Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.