Ghz (802.11B/G) - Cisco 7925G Series Deployment Manual

In this diagram, 5 GHz cells use a non-DFS channel while other nearby cells use DFS channels to permit maximum call
capacity under all conditions.
For 5 GHz, 20 channels are available in the Americas and 19 channels in Europe and Japan.
Where UNII-3 is available, it is recommend to use UNII-1, UNII-2 and UNII-3, 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)

In the 2.4 GHz (802.11b/g 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). In Japan, channel 14 can be
utilized as a fourth non-overlapping channel when using 802.11b access points.
Cisco Unified Wireless IP Phone 7925G Series Deployment Guide
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Minimum 20% Overlap
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