Cisco 8821 Manual page 66

On the 802.11 tab, configure the data rates as desired.
Is recommended to enable 12 Mbps as Mandatory and 18 Mbps and higher as Supported; however some environments may
require 6 Mbps to be enabled as a mandatory (basic) rate.
On the RRM tab, the Maximum Power Level Assignment and Minimum Power Level Assignment settings as well as other
TPC and Coverage Hole Detection settings can be configured.
On the High Density tab, Maximum Clients and Multicast Data Rates can be configured.
Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
66