OVERVIEW OF WIRELESS LANS

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 in college campus, in office building and in many public areas.

In this blog, we will read about 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 a 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 linklayers.

Architecture : The standard defines two kind of services; the Basic Service Set (BSS) and the Extended Service Set (ESS).

Basic Service Set (BSS) : 

IEEE 802.11 defines the Basic Service Set BSS) as the building block of a wireless LAN. A basic service set is made is stationery or mobile wireless stations known as the Access Point (AP).

The BSS without an AP is a standalone network and cannot send data to other BSSs. It is called an Adhoc Architecture. In this architecture, stations can form a network without need of an AP;they can locate one another and agree to be a part of BSS. A BSS with an AP is sometimes referred to as an infrastructure networl.

Extended Service Sets : 

An extended service set is made up of two or more BSS 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 Stationery. The mobile stations are not normal stations inside a BSS. The stationery stations are AP stations that are part of a wired LAN.

When BSSs are connected, the stations within the reach of one another can communicate without the use of an AP. However, communication between two stations in two different BSSs usually occurs via 2 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 mobility is either stationery 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 fro 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 Sublayer : The distributed coordination function and point coordination function. Figure