WLAN is a network technology which has all capabilities of a wired Local Area Network(LAN), but without any wires. It uses radio waves to transmit/receive information. The leading WLAN products use radio waves, typically in the license-free 2.4GHz band, to communicate digital information through the open air.

Currently there are three mail WLAN standards:

• IEEE 802.11b (Wi-Fi): 11 Mb/s data rate at 2.4 GHz
• IEEE 802.11a: 54 Mb/s data rate at 5 GHz
• IEEE 802.11g: 54 Mb/s data rate at 2.4 GHz

The principle of WLAN is to establish quick radio links between terminals connected to networks.This technology is facilitated by a number of components:

• PC Card: A Network adapter and integrated antenna that plugs into a peer, client, or server system’s expansion card slot. Clients can be desktops and laptop computers, file servers, printers, tape backup systems, and other office automation equipment.
  
  
• Ethernet Adapter: For peers, clients, or servers with pre-existing Ethernet network interface cards (NICs) or serial ports. This external module converts a wired client into a wireless client. Ethernet adapters plug directly into the client’s Ethernet NIC.
  
  
• Access Point (AP): An intelligent wireless “hub”. The access point manages wireless data traffic and controls the communication within the WLAN and between the wireless clients and the wired network.
  
  
• Bridge: These components use antennas to “bridge” across long distances, linking LANs wirelessly between buildings or within a building and communicate information between access points. Bridges can be used in a point-to-point or point-to-multipoint configuration.
  
  
• Antennas: These wireless signal boosters come in a number of formats specialized for the range and direction the wireless signal must take and for various strengths. Some antenna are integrated (e.g., in the wireless PC card and station adapter); others are external (e.g., wall-mounted or roof-mounted extension of a wireless bridge) for building-to-building communications.
  
  
• Signal Amplifiers: Spanning very long distances (e.g., between buildings) may require the use of signal amplifiers to bolster the wireless radio signal. Amplifiers are inserted in-line between the access point or bridge and antennas.

Infrastructure Mode : In this mode, Access Points are linked to a wired LAN. A typical Infrastructure mode deployment of WLAN is depicted below:

Ad-Hoc Mode: An Ad-Hoc mode is an on-demand WLAN without any access points. A typical Ad-Hoc mode deployment of WLAN is depicted below: