802.11a Standard
802.11a operates in the 5 GHz range and uses Orthogonal Frequency-
Division Multiplexing (OFDM). It has eight data rates: 6, 9, 12, 18, 24, 36,
48, and 54 Mbps. 802.11a provides from 12–23 nonoverlapping channels,
depending on country regulations. Portions of the 5 GHz range are allocated
to radar, so 802.11a uses Dynamic Frequency Selection (DFS) to check for
radar signals and choose a different channel if it detects them. It also uses
Transmit Power Control (TMC) to adjust client power, so that they use only
enough to stay in contact with the AP. DFS and TMC are part of the 802.11h
specification. Cisco recommends a maximum of 15 users per cell; expect an
actual peak throughput of about 32 Mbps.