Wednesday, June 1, 2011

WiFi Network

Each component of a WLAN requires a radio transceiver and antenna. Components are either stations or access points. Stations (STAs) are wireless LAN client radios. They can be incorporated into a LAN card installed in a desktop, a USB adapter, a PCMCIA or PC card, or can be integrated into the notebook or handheld device itself. Access Points (APs) form a bridge between wireless and wired LANs.

A Basic Service Set (BSS) is formed when two or more stations have recognized each other and established a network. The network can be configured in two basic ways:

  • Peer-to-peer (ad hoc mode) – This configuration is identical to its wired counterpart, except without the wires. Two or more STAs can talk to each other without an AP. When two or more stations form an ad hoc network, this is referred to as an Independent Basic Service Set (IBSS).
  • Client/Server (infrastructure networking) – This configuration consists of multiple stations connected to an AP, which acts as a bridge to a wired network. A BSS in this configuration is referred to as being in infrastructure mode.
An Extended Service Set (ESS) is formed when multiple overlapping BSSs (each containing an AP) are connected together by means of a distribution system, usually a wired Ethernet LAN. BSSs whose ranges overlap must transmit on different channels to avoid interference.

Range between STAs and APs is up to 100 m (depending on data rate), but the overall range of an ESS is limited only by the range of the wired distribution system. Also, ESSs can be further extended with wireless links up to several miles by the use of directional range extender antennas.

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