Cisco 7925G Deployment Manual page 71

If using 2.4 GHz, only channels 1, 6, and 11 should be enabled in the DCA list.
It is recommended to configure the 2.4 GHz channel for 20 MHz even if using Cisco 802.11n Access Points capable of 40 MHz
due to the limited number of channels available in 2.4 GHz.
Individual access points can be configured to override the global setting to use dynamic channel and transmit power assignment
for either 5 or 2.4 GHz depending on which frequency band is to be utilized.
Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G Deployment Guide
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