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See Also: Virtual LAN


A wireless LAN or '''WLAN''' is a Wireless Local Area Network , which is the linking of two or more computers without using wires. WLAN utilizes Spread-spectrum or OFDM (802.11a) modulation technology based on Radio Waves to enable communication between devices in a limited area, also known as the basic service set. This gives users the mobility to move around within a broad coverage area and still be connected to the network.



HISTORY


"In 1979, F.R. Gfeller and U. Bapst published a paper in the IEEE Proceedings reporting an experimental wireless local area network using diffused Infrared communications. Shortly thereafter, in 1980, P. Ferrert reported on an experimental application of a single code Spread Spectrum radio for wireless terminal communications in the IEEE National Telecommunications Conference. In 1984, a comparison between Infrared and CDMA spread spectrum communications for wireless office information networks was published by [ Kaveh Pahlavan ] in IEEE Computer Networking Symposium which appeared later in the IEEE Communication Society Magazine. In May 1985, the efforts of Marcus led the FCC to announce experimental ISM bands for commercial application of spread spectrum technology. Later on, M. Kavehrad reported on an experimental wireless PBX system using code division multiple access. These efforts prompted significant industrial activities in the development of a new generation of wireless local area networks and it updated several old discussions in the portable and mobile radio industry.

On July 21 , 1999 , AirPort debuted at the Macworld Expo in New York City with Steve Jobs picking up an IBook supposedly to give the cameraman a better shot as he surfed the Web. Applause quickly built as people realized there were no wires. This was the first time Wireless LAN became publicly available at consumer pricing and easily available for home use. Before the release of the Airport, Wireless LAN was too expensive for consumer use and used exclusively in large corporate settings.

Originally WLAN hardware was so expensive that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by standards, primarily the various versions of IEEE 802.11 ( Wi-Fi ). An alternative ATM -like 5 GHz standardized technology, HIPERLAN , has so far not succeeded in the market, and with the release of the faster 54 Mbit/s 802.11a (5 GHz) and 802.11g (2.4 GHz) standards, almost certainly never will.


BENEFITS

The popularity of wireless LANs is a testament primarily to their convenience, cost efficiency, and ease of integration with other networks and network components. The majority of computers sold to consumers today come pre-equipped with all necessary wireless LAN technology.

The benefits of wireless LANs include:

  • ''Convenience'': The wireless nature of such networks allows users to access network resources from nearly any convenient location within their primary networking environment (home or office). With the increasing saturation of laptop-style computers, this is particularly relevant.


  • ''Mobility'': With the emergence of public wireless networks, users can access the internet even outside their normal work environment. Most chain coffee shops, for example, offer their customers a wireless connection to the internet at little or no cost.


  • ''Productivity'': Users connected to a wireless network can maintain a nearly constant affiliation with their desired network as they move from place to place. For a business, this implies that an employee can potentially be more productive as his or her work can be accomplished from any convenient location.


  • ''Deployment'': Initial setup of an infrastructure-based wireless network requires little more than a single Access Point . Wired networks, on the other hand, have the additional cost and complexity of actual physical cables being run to numerous locations (which can even be impossible for hard-to-reach locations within a building).


  • ''Expandability'': Wireless networks can serve a suddenly-increased number of clients with the existing equipment. In a wired network, additional clients would require additional wiring.


  • ''Cost'': Wireless networking hardware is at worst a modest increase from wired counterparts. This potentially increased cost is almost always more than outweighed by the savings in cost and labor associated to running physical cables.



DISADVANTAGES

Wireless LAN technology, while replete with the conveniences and advantages described above, has its share of downfalls. For a given networking situation, wireless LANs may not be desirable for a number of reasons. Most of these have to do with the inherent limitations of the technology.

  • ''Security'': Wireless LAN transceivers are designed to serve computers throughout a structure with uninterrupted service using radio frequencies. Because of space and cost, the antennas typically present on wireless networking cards in the end computers are generally relatively poor. In order to properly receive signals using such limited antennas throughout even a modest area, the wireless LAN transceiver utilizes a fairly considerable amount of power. What this means is that not only can the wireless packets be intercepted by a nearby adversary's poorly-equipped computer, but more importantly, a user willing to spend a small amount of money on a good quality antenna can pick up packets at a remarkable distance; perhaps hundreds of times the radius as the typical user. In fact, there are even computer users dedicated to locating and sometimes even cracking into wireless networks, known as .)''


  • ''Range'': The typical range of a common 802.11g network with standard equipment is on the order of tens of meters. While sufficient for a typical home, it will be insufficient in a larger structure. To obtain additional range, Repeater s or additional access points will have to be purchased. Costs for these items can add up quickly. Other technologies are in the development phase, however, which feature increased range, hoping to render this disadvantage irrelevant. (See WiMAX )


  • ''Reliability'': Like any radio frequency transmission, wireless networking signals are subject to a wide variety of Interference , as well as complex propagation effects (such as Multipath , or especially in this case Rician Fading ) that are beyond the control of the network administrator. In the case of typical networks, Modulation is achieved by complicated forms of Phase-shift Keying (PSK) or Quadrature Amplitude Modulation (QAM), making interference and propagation effects all the more disturbing. As a result, important network resources such as Servers are rarely connected wirelessly.


  • ''Speed'': The speed on most wireless networks (typically 1-108 Mbit/s) is reasonably slow compared to the slowest common wired networks (100 Mbit/s up to several Gbit/s). There are also performance issues caused by TCP and its built-in Congestion Avoidance . For most users, however, this observation is irrelevant since the speed bottleneck is not in the wireless routing but rather in the outside network connectivity itself. For example, the maximum ADSL throughput (usually 8 Mbit/s or less) offered by telecommunications companies to general-purpose customers is already far slower than the slowest wireless network to which it is typically connected. That is to say, in most environments, a wireless network running at its slowest speed is still faster than the internet connection serving it in the first place. However, in specialized environments, the throughput of a wired network might be necessary. Newer standards such as 802.11n are addressing this limitation and will support peak throughputs in the range of 100-200 Mbit/s.




    • ARCHITECTURE


    Stations

    All components that can connect into a wireless medium in a and clients.

    • Access points

      • :Access points (APs) are base stations for the wireless network. They transmit and receive radio frequencies for wireless enabled devices to communicate with.


    • Clients

      • :Wireless clients can be mobile devices such as laptops, personal digital assistants, IP Phones , or fixed devices such as Desktops and Workstation s that are equipped with a wireless network interface.



    Basic service set

    The basic service set (BSS) is a set of all stations that can communicate with each other. There are two types of BSS: independent BSS and infrastructure BSS. Every BSS has an identification (ID) called the BSSID, which is the MAC Address of the access point servicing the BSS.

    • Independent basic service set

      • :An independent BSS is an Ad-hoc Network that contains no access points, which means they can not connect to any other basic service set.


    • Infrastructure basic service set

      • :An infrastructure BSS can communicate with other stations not in the same basic service set by communicating through access points.



    Extended service set

    An extended service set (ESS) is a set of connected BSSes. Access points in an ESS are connected by a distribution system. Each ESS has an ID called the SSID which is a 32-byte (maximum) character string. For example, "linksys" is the default SSID for Linksys routers.


    Distribution system

    A distribution system connects access points in an extended service setup.


    TYPES OF WIRELESS LANS


    Peer-to-peer


    A Peer-to-peer (P2P) 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.

    802.11 specs define the physical layer (PHY) and MAC (Media Access Control) layers. However, unlike most other IEEE specs, 802.11 includes three alternative PHY standards: diffuse infrared operating at 1 Mbit/s in; frequency-hopping spread spectrum operating at 1 Mbit/s or 2 Mbit/s; and direct-sequence spread spectrum operating at 1 Mbit/s or 2 Mbit/s. A single 802.11 MAC standard is based on CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). The 802.11 specification includes provisions designed to minimize collisions. Because two mobile units may both be in range of a common access point, but not in range of each other.
    The 802.11 has two basic modes of operation: Ad hoc mode enables peer-to-peer transmission between mobile units. Infrastructure mode in which mobile units communicate through an access point that serves as a bridge to a wired network infrastructure is the more common wireless LAN application the one being covered. Since wireless communication uses a more open medium for communication in comparison to wired LANs, the 802.11 designers also included a shared-key encryption mechanism, called wired equivalent privacy ( WEP ), or Wi-Fi Protected Access, ( WPA, WPA2 ) to secure wireless computer networks.


    Bridge

    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

    See Also: Wireless Distribution System



    When it is difficult to connect all of the access points in a network by wires, it is also possible to put up access points as repeaters.


    SEE ALSO




REFERENCES


Que. “Comparing 802.11 a, b, and g: Channels and Interference.”
Quepublishing. September 9, 2005.

Kissane, Simon. “Global System for Mobile Communications.” Wikipedia. 6 February 2007.

“How does satellite Internet operate?” How Stuff Works.

“PC card.” Wikipedia. 9 February 2007 .

Webopedia. “Wireless Networking Standards.” Webopedia. September 02 , 2005 .
By Giriz - VesterDFG

Petrick, Al and Bob O'Hara. "The IEEE 802.11 Handbook: A Designer's Companion". IEEE. March 2005.

WLAN Phishing using SSIDs

Lecture on Wireless Lan Hacks at Wright State Uni.

Community and Amateur WLAN "not for proft community internet access"



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