Saturday, February 5, 2011

Wireless, Wireless LANs, LAN Arcitecture,IEEE 802.11

What is Wireless LAN, Wireless LAN overview.

The wireless LAN (WLAN) is a wireless local area network that communicate two or more computers or devices using spread-spectrum or OFDM modulation technology based to enable Links between devices in a limited area or local area. That helps users to move in mobility around within a broad coverage area and still be connected to the network.

Easy Installation system make the WLAN very popular for the Home users, and For its mobility features It is best for the Laptop users. Public businesses Like shops, coffe shops, malls have begun to offer wireless access to their customers; some are even provided as a free service. Large wireless network projects are being put up in many major cities: New York City, Salt lake city in INDIA for instance, has begun a pilot program to cover all five boroughs of the city with wireless Internet access.

Source : wikipedia

Wireless LANs


Wireless communication is one of the fastest-growing technologies. The demand for connecting devices without the use of cables is increasing everywhere. Wireless LANs can be found on college campuses, in office buildings, and in many public areas. In this chapter, we concentrate on two promising wireless technologies for LANs: IEEE 802.11 wireless LANs, sometimes called wireless Ethernet, and Bluetooth, a technology for small wireless LANs. Although both protocols need several layers to operate, we concentrate mostly on the physical and data link layers.
IEEE 802.11

IEEE has defined the specifications for a wireless LAN, called IEEE 802.11, which covers the physical and data link layers.
Architecture

The standard defines two kinds of services: the basic service set (BSS) and the extended service set (ESS). Basic Service Set IEEE 802.1 ] defines the basic service set (BSS) as the building block of a wireless LAN. A basic service set is made of stationary or mobile wireless stations and an optional central base station, known as the access point (AP).

The BSS without an AP is a stand-alone network and cannot send data to other BSSs. It is called an ad hoc architecture. In this architecture, stations can form a network without the need of an AP; they can locate one another and agree to be part of a BSS. A BSS with an AP is sometimes referred to as an infrastructure network.
Extended Service Set

An extended service set (ESS) is made up of two or more BSSs with APs. In this case, the BSSs are connected through a distribution system, which is usually a wired LAN. The distribution system connects the APs in the BSSs. IEEE 802.11 does not restrict the distribution system; it can be any IEEE LAN such as an Ethernet. Note that the extended service set uses two types of stations: mobile and stationary. The mobile stations are normal stations inside a BSS. The stationary stations are AP stations that are part of a wired LAN. When BSSs are connected, the stations within reach of one another can communicate without the use of an AP. However, communication between two stations in two different BSSs usually occurs via two APs. The idea is similar to communication in a cellular network if we consider each BSS to be a cell and each AP to be a base station. Note that a mobile station can belong to more than one BSS at the same time.
Station Types
IEEE 802.11 defines three types of stations based on their mobility in a wireless LAN: no-transition, BSS-transition, and ESS-transition mobility. A station with no-transition mobility is either stationary (not moving) or moving only inside a BSS. A station with BSS-transition mobility can move from one BSS to another, but the movement is confined inside one ESS. A station with ESS-transition mobility can move from one ESS to another. However, IEEE 802.11 does not guarantee that communication is continuous during the move.
MAC Sublayer

IEEE 802.11 defines two MAC sublayers: the distributed coordination function (DCF) and point coordination function (PCF).

Benifits of Wireless LANs -

Today The use and the popularity of Wireless Lan is Increasing very fast, Why Everyone is using such a System Let us see -

Convenience : For its Wireless facility Every one can access this network from anywhere or any convenient location or Home and office. For the Laptop Style computers This is best and relevant.
Mobility :Mobility features is the best features of WLANs, Any one can use this network in any where like Coffee shops, Shopping Mall, User can use it outside of their normal work place. This WLANs are cost effective also.

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