RRM tuning

RRM, Radio Resources Management, is the ability that a controller has to control APs Power level and Channel values. An AP needs to be surrounded by at least 3 other APs hearing this first AP at -70dBm or better, for the RRM algorithm to be triggered on the controller. In other words, if any of your AP has only 2 other APs in its neighbourhood (or at least 2 APs heard at -70 dBm or better), the WLC will not change the AP power level.
To determine the number of neighbouring APs and their power level, the system relies on RRM neighbour messages, sent by all APs every 60 seconds by default, at max power and lowest mandatory rate. All other APs hearing the RRM message forward it to their controller. As each RRM neighbour message is signed, each controller can recognize if it was sent by a known AP in the RF Group and identify the AP along with which APs reported (= heard) the message, with what power level. Smart, he?
Now what can we tune here? 2 things:
- How often the RRM neighbour messages are sent.
- What is the threshold that triggers the RRM algorithm.

Remember the defaults? RRM messages are sent every 60 seconds, and you need 3 neighbouring APs hearing this AP at -70 dBm to trigger the algorithm. You cannot change this "3 APs" value.

To change how often the RRM neighbour messages are sent, from your controller GUI, navigate to Wireless > 82.11a > RRM > General. Change the Neighbor Packet Frequency from 60 to the new interval you want to use. As you can guess, this is done on a per radio basis, do the same for 82.11b/g if you want to.



That's for the RRM neighbour message frequency. The RRM algorithm threshold cannot be changed from the GUI, but from the CLI. In your controller CLI, type:
(Cisco Controller) >config advanced 802.11a tx-power-control-threshold ?
Enter a value between (-50) and (-80)
And change the value to what is best. For example:
Cisco Controller) >config advanced 802.11a tx-power-control-threshold -79
You can of course use the "show advanced 82.11a tx-power-control-threshold" command to verify the current value. This changes the threshold for 82.11a, you need the same command for 82.11b/g if required.
You can see the value of this threshold from the GUI, under Wireless > 82.11a > RRM TPC.
Before:




After!

OTAP - Over the Air Provisioning

You probably know OTAP, over the air provisioning of APs. When an access point boots, it can listen to the Air and receive information about controllers from the other APs. Do you want to know what does an OTAP message look like? How to read your controller IP address from a capture?
Watch here: http://www.youtube.com/watch?v=dZHiY_1p_d0
Imagine... you are in a lab, and the scenario says "your controller blahblah Management IP address was lost. Use the OTAP capture to find it. And basically if you can't find it, you can't get to it and configure it and this means the end of the journey for your lab..." you'd better be able to decipher OTAP messages, just in case!

Disclaimer: I DON'T know if this scenario is part of an actual lab or not! I just feel that at CCIE level, you are probably expected to understand OTAP well enough to know how to use it!
:-)