IEEE 802.11 Architecture
- The smallest building block of a wireless LAN is a basic service set (BSS), which consists of some number of stations executing the same MAC protocol and competing for access to the same shared wireless medium.
- A BSS may isolated or it may connect to a backbone distribution system (DS) through an access point (AP).
- The AP functions as a bridge and a relay point. In a BSS, client stations do not communicate directly with one another.
- Rather, if one station in the BSS wants to communicate with another station in the same BSS, the MAC frame first sent from the originating station to the AP, and then from the AP to the destination station.
- Similarly, a MAC frame from a station in the BSS to a remote station sent from the local station to the AP and then relayed by the AP over the DS on its way to the destination station.
- The BSS generally corresponds to what referred to as a cell in the literature. The DS can a switch, a wired network, or a wireless network.
- When all the stations in the BSS mobile stations, with no connection to other BSSs, the BSS called an independent BSS (IBSS).
An IBSS is typically an ad hoc network. In an IBSS, the stations all communicate directly, and no AP involved.
- A simple configuration is shown in Figure, in which each station belongs to a single BSS; that is, each station is within wireless range only of other stations within the same BSS.
- It is also possible for two BSSs to overlap geographically so that a single station could participate in more than one BSS.
- Further, the association between a station and a BSS dynamic. Stations may turn off, come within range, and go out of range.
- An extended service set (ESS) consists of two or more basic service sets interconnected by a distribution system.
- Typically, the distribution system a wired backbone LAN but can any communications network.
- The extended service set appears as a single logical LAN to the logical link control (LLC) level.
- The figure indicates that an access point (AP) implemented as part of a station; the AP the logic within a station that provides access to the DS by providing DS services in addition to acting as a station.
- To integrate the IEEE 802.11 architecture with a traditional wired LAN, a portal used. The portal logic implemented in a device, such as a bridge or a router. That part of the wired LAN and that attached to the DS.