Figure
illustrates
that, as a client roams away from the access point, the transmission signals
between the two attenuate (weaken). Rather than decreasing reliability, the AP
shifts to a slower data rate, which gives more accurate data transfer. This is
called data rate or multi-rate shifting. As a client moves away from an 802.11b
access point, the data rate will go from 11 Mbps, to 5.5Mbps, to 2 Mbps, and,
finally, to 1 Mbps. This happens without losing the connection, and without any
interaction from the user. The same thing occurs with 802.11a. However, as
Figure
shows,
the data rates step down from 54 Mbps. Figure
also
shows the approximate distances from the AP, for each data rate.
The
Cisco Aironet 2.4 GHz radio delivers 100 mW of output and offers a high degree
of receiver sensitivity. The 5 GHz client radio has a 20 mW transmit power and
the 5 GHz access point has a 40 mW transmit power. It is possible to adjust the
power level down, to create pico-cells, or smaller coverage cells. This would
be done, for example, to prevent the coverage area of one AP from extending too
far into the coverage area of another AP.