The default channel setting for the wireless device radios is least congested.
At startup, the wireless device scans for and selects the least-congested channel. For the most consistent performance after a site survey, however, we recommend assigning a static channel setting for each Access Point (AP). The channel settings on the wireless device correspond to the frequencies available in your regulatory domain. See the AP's hardware installation guide for the frequencies allowed in your domain.
Using the least congested channel improves roaming characteristics and ensures proper functionality of the Wireless devices. Use only non-overlapping channels to program the APs. When configuring the AP, disable the option to search for the least-congested channel. Cisco recommends that administrators manually set all RF channels according to the data gathered during the site survey and site survey verification steps.
If you use the option to select the least-congested channel, the AP will change to a different channel every time its power is reset, leaving no predictability and negating the time and effort spent on the site survey. Random selection of channels causes roaming times to increase because the wireless client devices (such as wireless phone) have to scan all channels rather than a smaller subgroup of active channels.
Every regulatory domain specifies different allowable radio channels. Always use channels that are a minimum of five radio channels apart so that they do not overlap. (For example, use channels 1, 6, and 11 or use 2, 7, and 12.) This practice reduces the ambient noise on each channel. For best practices in RF deployments and for information on how to avoid common problems, refer to Site Survey RF Recommendations
Note: In certain situations, data rates below 11 Mbps must be enabled for legacy devices. This lower speed affects voice quality and the RF environment, and it is not the recommended setting. If you have to enable both 11 Mbps and 2 Mbps, these low speeds reduce the number of simultaneous calls that each AP can handle and also increase the overlap because they extend the range of the APs.
Note: Too many APs in the same vicinity creates radio congestion that can reduce throughput. A careful site survey can determine the best placement of APs for maximum radio coverage and throughput.