Coverage Hole Detection Question

[brettp]

I have read a good many articles about about CHD and every one basically uses the same or similar wording:

“Coverage hole detection is based on a 5 second (CHD measurement period) histogram of each Clients Received RSSI values maintained by the AP”

“Each individual controller performs coverage hole detection monitoring all associated AP's and thus monitoring every attached client and their received signal levels.”

Can someone please tell me what does “client’s received RSSI values” or “received signal levels” mean? Does the wireless client send its RSSI (as in signal strength FROM the AP TO the client) to the AP/WLC for accounting… or does it refer to the AP’s RSSI (as in signal strength FROM the client TO the AP?) In terms of CHDM, I understand there is an algorithm used that ultimately, if necessary, causes the AP to boost its signal to compensate to a poor signal. This would make sense if the wireless client sends its RSSI to the AP… but how does that make sense if it’s the RSSI from the APs perspective? Why would boosting the signal help if the AP has poor reception? Or, is this based on the assumption that is reception is bad one way, it probably is the other way too?

Thanks!

[Rasika Nayanajith · Accepted solution]

Does the wireless client send its RSSI (as in signal strength FROM the AP TO the client) to the AP/WLC for accounting..

No client is not sending its RSSI values to AP.

or does it refer to the AP’s RSSI (as in signal strength FROM the client TO the AP?)

AP will estimate client RSSI based on how strong AP hears the client. The client will not send its actual RSSI in out of band communication.

slide 32-33 has some useful information on this matter.

https://www.ciscolive.com/c/dam/r/ciscolive/emea/docs/2016/pdf/BRKEWN-2000.pdf 

This would make sense if the wireless client sends its RSSI to the AP… but how does that make sense if it’s the RSSI from the APs perspective? Why would boosting the signal help if the AP has poor reception? Or, is this based on the assumption that is reception is bad one way, it probably is the other way too?

The general assumption is, if a wireless client had good RSSI and suddenly it dropped (due to an AP failure), then WLC will increase the power of nearby AP to fill the coverage gap.

HTH

Rasika

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[brettp]

Thank you for the information and explanation!