RRM (Radio Resource Management) Overview

The RRM feature is also known as Auto-RF or act as a built –in RF engineer in controller, uses the RF information gathered by the APs to make decisions on whether channel assignment or power levels need to be adjusted.

In other words: It uses the RF information gathered by the APs to make decisions on whether channel assignment or power levels need to be adjusted. Just because the RF environment has changed does not necessarily mean that the controller will change.

Before covering the intricacies of the RRM algorithm and RF grouping, following is a high-level overview of the basic workflow involved:

Step 1: The controllers and their APs use the configured RF group name to determine if other APs they hear are part of their RF group.

Step 2: The APs use neighbor messages (sent every 60 seconds) that are authenticated by other APs that hear them. The neighbor messages include information about the AP, the controller, and the configured RF group name.

Step 3: The APs that hear the neighbor message of another AP authenticate that message using the RF group name and pass it to their respective controller.

Step 4: The controllers use this information to determine what other controllers should be in their RF group, and then form logical groups to share the RF information from their respective APs, and elect an RF group leader.

Step 5: The RF group leader runs the RRM algorithm against the RF information from all the APs in the RF group. Depending on the outcome, a power level or channel change for an AP or group of APs might take place.

To know more details about RRM, check this previous post:

https://rscciew.wordpress.com/2013/12/04/radio-resource-management/

Also don’t forget to see these YouTube video by Jerome Henry:

1. http://www.youtube.com/watch?v=gwCxVwmHnRw – describes RRM principles
2. http://www.youtube.com/watch?v=XhmnXeeLQBc – goes deeper into RRM and provides useful information if you are to take a Cisco exam on Wireless related topics! 🙂
3. http://www.youtube.com/watch?v=3EnvhxjzEWU – details how RRM controls the AP channel assignment with DCA (Dynamic Channel Assignment).
4. http://www.youtube.com/watch?v=32YWzuXTg5M – explains how RRM dynamically reduces AP power with TPC (Transmit Power Control)
5. http://www.youtube.com/watch?v=yot63RsKOCg – explains how the Radio Coverage Detection Algorithm works.

RRM feature enables controllers to continually monitor their associated LAP for the following information:

• Traffic load: The total bandwidth used for transmitting and receiving traffic. It enables wireless LAN managers to track and plan network growth ahead of client demand.
• Interference: The amount of traffic coming from other 802.11 sources.
• Noise: The amount of non-802.11 traffic that is interfering with the currently assigned channel.
• Coverage: The received signal strength (RSSI) and signal-to-noise ratio (SNR) for all connected clients.
• Other: The number of nearby access points.

RRM performs these functions:

• Radio resource monitoring
• Transmit power control
• Dynamic channel assignment
• Coverage hole detection and correction

In this post we will see the configuration guide of RRM on WLC.

Configure an RF Group Name

Via GUI:

First step to configure RRM is to ensure WLC has the RF Group Name configured. This can be done through the controller web interface. Go to Controller > General and then type a RF Group Name value.

Via CLI:

Create an RF group by entering the config network rf-network-name name command:

(WLAN1) >config network rf-network-name mywlc

Configuring the RF Group Mode:

Via GUI

Go to Wireless > 802.11a/n or 802.11b/g/n > RRM > RF Grouping

Via CLI:

config advanced {802.11a | 802.11b} group-mode {auto | leader| off | restart}

(WLAN1) >config advanced 802.11a group-mode ?
 auto           Sets the 802.11a RF group selection to automatic update mode.
 leader         Sets the 802.11a RF group selection to static mode, and sets this controller as the group leader.
 off            Sets the 802.11a RF group selection off.
 restart        Restarts the 802.11a RF group selection.
(WLAN1) >config advanced 802.11a group-mode auto

On this screen we can see the details of RF group

Group Mode: Auto (It can be static or we can disable it)

Group Role: Auto Leader or Static Leader

Group Update Interval: The group update interval value indicates how often the RF Grouping algorithm is run and it cannot be modified.

Group Leader: This field displays the IP Address of the WLC that is currently the RF Group Leader.

Last Group Update: The RF Grouping algorithm runs every 600 seconds (10 minutes). This field indicates the time (in seconds) since the algorithm last ran.

*** A configured static leader cannot become a member of another controller until its mode is set to “auto”.

No we will change the Group mode on Controller”WLAN1” as leader.

Add a controller as member:

Via CLI:

Add a controller as a static member of the RF group (if the mode is set to “leader”) by entering this command:

config advanced {802.11a | 802.11b} group-mode {auto | leader| off | restart}

(WLAN1) >config advanced 802.11agroup-mode leader

config advanced 802.11a | 802. group-member add controller_name controller_ip_address

(WLAN1) >config advanced 802.11a | 802. group-member add WLAN2 10.35.80.3

To see RF grouping status

(WLAN1) >show advanced 802.11a group
 Radio RF Grouping
 802.11a Group Mode............................. STATIC
 802.11a Group Update Interval.................. 600 seconds
 802.11a Group Leader........................... WLAN1 (10.35.80.1)
 802.11a Group Member......................... WLAN1 (10.35.80.1)
 802.11a Group Member......................... WLAN2 (10.35.80.3)
 802.11a Last Run............................... 17 seconds ago
 * indicates member has not joined the group.
 (WLAN1) >

*** Same procedure for 802.11b network

***Info:

There are few things we must take care before forcing a WLC to be a RF leader:

1. All WLC members must have the same mobility and RF group name.
2. All WLCs AP must be in the range of each other.

In next post we will learn TPC, DCA and CHD.

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