In the release 8.1 of Cisco Wireless LAN Controller, a new feature has been introduced called Dynamic Bandwidth Selection (DBS). This algorithm is aimed to improve the channel reuse pattern and overall help improve the performance of the Wireless network as a whole.
The 802.11ac standard introduced wider channel width like 80MHz, 160MHz and 80+80 MHz. In environments where 11ac and 11n (and legacy) networks exists simultaneously, the channel reuse can become an issue. Due to the static nature of the channel width (40MHz, 80MHz etc), there can be an overlap of 11ac APs on a particular 80MHz channel and 11n or legacy AP serving on a subset of that 80MHz channel. DBS allows 11ac APs operating on higher channel widths like 80MHz and 160MHz (future), to change the operating channel width lower / narrower bandwidths such as 20MHz or 40MHz. This is particularly useful for networks that have 11ac APs along with legacy APs and or clients, which only have the narrower bandwidths.
The DBS algorithm provides a smooth transition for customers who are upgrading from 11n to 11ac. The down shifting to narrower bandwidths happen based on two factors, neighboring APs and clients (11n).
  • When client stations are all 11n (or above a certain preset threshold hysteresis) or there are traffic flow types that favor narrower bandwidth: change the 80MHz 11ac BSS to narrower 40MHz channel widths (that is, DBS with bandwidth constraint).
  • When there is a mix of 11n and 11ac client stations (depending on a preset threshold hysteresis): Allow sharing secondary 40MHz bandwidth between 80MHz BSS (that is DBS with misaligned primary 40MHz channel).
  • When clients are not in the picture (without clients), the DBS algorithm factors in the proximity of the APs (80MHz) and neighbor signal strength. If the algorithm thinks there is excess co channel interference (APs too close of each other), the algorithm may change the APs to operate on narrower widths of 40MHz and 20MHz.

Enabling Dynamic Bandwidth Selection (DBS)
  1. Disable 802.11a network.
  2. Go to Wireless > 802.11a > RRM > DCA.
  3. In the Channel Width field, click the Best radio button.

4. Enable 802.11a network.

  1. Create an RF Profile on 802.11a radio.

3. Apply the RF Profile to AP groups.

  • A global restart should be initiated when DBS is enabled.
    • config 802.11a channel globabl restart.