Campus lan and Wireless lan solution Design Guide

Cisco Flexible Radio Assignment 
Cisco FRA is a feature that takes advantage of hardware choices available in the Cisco Catalyst 9100 Series 
APs. As described for band selection, there are limitations using the 2.4 GHz spectrum. If you are deploying 
APs for optimal 5 GHz coverage and density, you will likely have an unnecessarily high density of 2.4 GHz radios 
and their limited channel selection options, which will cause interference issues. Cisco FRA measures this and 
identifies APs whose 2.4 GHz radio can be selectively assigned to a role that optimizes the use of the RF 
spectrum. 

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Cisco FRA first identifies redundant APs and then manages the changing of the single XOR radio to another 
band. Cisco FRA relies on hardware capabilities as well as existing DCA in order to manage the switching of 
interface roles. Cisco FRA also provides a new metric, Coverage Overlap Factor, that admins can use to 
manually select and configure redundant radios within the deployment. 
Coverage Hole Detection and Mitigation algorithm 
The RRM CHDM algorithm detects areas of weak radio coverage in a WLAN that are below the level needed for 
robust radio performance. This feature can alert you to the need for an additional or relocated AP. 
If clients associated to an AP are detected at threshold levels lower than those specified in the RRM 
configuration, the AP sends a “coverage hole” alert to the controller. The thresholds include RSSI, failed client 
count, percentage of failed packets, and number of failed packets. The alert indicates the existence of an area 
where clients are continually experiencing poor signal coverage without having a viable AP to which to roam. 
The controller discriminates between coverage holes that can and cannot be corrected. For coverage holes that 
can be corrected, the controller mitigates the coverage hole by increasing the transmit power level for a specific 
AP that can improve the coverage. For clients that are making poor roaming decisions (referred to as 
sticky 
clients
), the CHDM algorithm reports a false positive. System validation ensures that a client really does have 
better coverage on the new AP and is not just unnecessarily moving to that new AP for an arbitrary reason.