Ghz (802.11B/G/N) - Cisco 8800 Series Deployment Manual

For 5 GHz, 21 channels are available in the Americas and 16 channels in Europe and Japan.
Where UNII-3 is available, it is recommended to use UNII-1, UNII-2, and UNII-3 only to utilize a 12 channel set.
If planning to use UNII-2 extended channels (channels 100 - 140), it is recommended to disable UNII-2 (channels 52-64) on the
access point to avoid having so many channels enabled.
Having many 5 GHz channels enabled in the wireless LAN can delay discovery of new access points.

2.4 GHz (802.11b/g/n)

In the 2.4 GHz (802.11b/g/n) environment, only non-overlapping channels must be utilized when deploying VoWLAN. Non-
overlapping channels have 22 MHz of separation and are at least 5 channels apart.
There are only 3 non-overlapping channels in the 2.4 GHz frequency range (channels 1, 6, 11).
Cisco IP Phone 8800 Series Wireless LAN Deployment Guide
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