802.11 Standards
Wireless LAN general description

WLANs
Wireless networks have fundamental characteristics that make them significantly different from traditional wired LANs. Some countries impose specific requirements for radio equipment in addition to those specified in the 802.11 standard.

On wired LANs, a MAC address equates to a physical location. This is implicitly assumed in the design of wired LANs. In IEEE 802.11, the addressable unit is a station (STA). The STA is a message destination, but it is generally not a fixed physical location, as shown in Figure .

The physical layers used in IEEE 802.11 are fundamentally different from those used with wired media. The following is true about the IEEE 802.11 PHY protocols: Figure

  • They use a medium that has neither absolute nor readily observable boundaries, outside of which stations will be unable to send or receive network frames.
  • They are unprotected from outside signals.
  • They communicate over a medium that is significantly less reliable than wired media.
  • They have dynamic topologies.
  • They lack full connectivity. Normally, the assumption is made that every STA can hear every other STA. This assumption is invalid for WLANs. STAs may be hidden from each other.
  • They have time-varying and asymmetric propagation properties.

Because of limitations on wireless PHY ranges, WLANs needing to cover reasonable geographic distances must be built up from basic coverage building blocks.

One of the requirements of IEEE 802.11 is to handle mobile as well as portable stations. A portable station is one that is moved from location to location, but is only used while at a fixed location. Mobile stations actually access the LAN while in motion. It is not sufficient to handle only portable stations, since propagation effects blur the distinction between portable and mobile stations. Fixed stations often appear to be mobile, due to these propagation effects.

Another aspect of mobile stations is that they are often battery powered. Therefore power management is an important consideration. For example, it cannot be presumed that a station receiver will always be powered on.

IEEE 802.11 is required to appear to higher layers, such as LLC, as an IEEE 802 LAN. The IEEE 802.11 network must handle station mobility within the MAC sublayer.