Area concepts

Area concepts

For wireless PHYs, well-defined coverage areas simply do not exist. Propagation characteristics are
dynamic and unpredictable. Small changes in position or direction may result in dramatic differences in
signal strength. Similar effects occur whether a STA is stationary or mobile (as moving objects may impact
station-to-station propagation).
Figure 4-4 shows a signal strength map for a simple square room with a standard metal desk and an open
doorway. Figure 4-4 is a static snapshot; the propagation patterns change dynamically as STAs and objects
in the environment move. In Figure 4-4 the dark (solid) blocks in the lower left are a metal desk and there is
a doorway at the top right of the figure. The figure indicates relative differences in field strength with
different intensities and indicates the variability of field strength even in a static environment. The
difference between the greatest signal strength and the least signal strength in Figure 4-4 is 50 dB.
While the architecture diagrams show sharp boundaries for BSSs, this is an artifact of the pictorial
representation, not a physical reality. Because dynamic three-dimensional field strength pictures are difficult
to draw, well-defined shapes are used by IEEE 802.11 architectural diagrams to represent the coverage of a
BSS.
Further description difficulties arise when attempting to describe collocated coverage areas. Consider
Figure 4-5, in which STA 6 could belong to BSS 2 or BSS 3.
While the concept of sets of STAs is correct, it is often convenient to talk about areas. For many topics the
concept of area is sufficient. Volume is a more precise term than area, though still not technically correct.
For historical reasons and convenience, this standard uses the common term area.


Integration with wired LANs
To integrate the IEEE 802.11 architecture with a traditional wired LAN, a final logical architectural
component is introduced—a portal.
A portal is the logical point at which MSDUs from an integrated non-IEEE-802.11 LAN enter the
IEEE 802.11 DS. For example, a portal is shown in Figure 4-6 connecting to a wired IEEE 802 LAN.

All data from non-IEEE-802.11 LANs enter the IEEE 802.11 architecture via a portal. The portal is the
logical point at which the integration service is provided. The integration service is responsible for any
addressing changes that might be required when MSDUs pass between the DS and the integrated LAN. It is
possible for one device to offer both the functions of an AP and a portal.