WLAN controller redundancy

Question

We have a site with 3 controllers it's serveral miles between them. And have think about to deploy a N+1 solution. My question is if the controllers must have same RF group. I know they must have same mobility group!. Can you have several mobilty groups on one controller?

Answer 1

Hi Klas,
Have a look at this good doc for RRM Management. Hopefully this will clear things up;
In a scenario where multiple controllers are configured with the same RF Group Name, but their respective APs cannot hear each other's neighbor messages, two separate, top-level RF Groups are formed.
RF Grouping happens at the controller level. This means that once APs report information to their controllers on the other APs they hear, and the controllers to which those APs are connected, each respective WLC communicates directly with the other WLCs to form a system-wide grouping. Within a single system-wide group, or RF Group, many subsets of APs can have their RF parameters set independently of each other. For instance, consider a scenario where one central WLC has individual APs at remote sites. In this case, each AP has its RF parameters set separately of the others. While each AP belongs to the same controller RF Grouping, each individual AP in this example is in its own logical RF sub-Group.
APs each compile and maintain a list of up to 34 neighboring APs per radio. This list is then reported up to their respective controllers. Each WLC maintains a list of 24 neighbors per AP radio from the neighbor messages sent by each AP. Once at the controller level, this per-AP, per-radio neighbor list of up to 34 APs is pruned. The ten APs with the weakest signals are dropped. WLCs then forward each AP neighbor list up to the RF Group Leader, the WLC elected by the RF Group in order to perform all RRM configuration decision-making.
From this good doc;
Radio Resource Management under Unified Wireless Networks
http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008072c759.shtml
These are the Group settings available through the WLC GUI:
Group Mode The Group Mode setting allows RF Grouping to be disabled. When this feature is disabled, the WLC cannot group with other controllers in order to perform system-wide RRM functionality. Disabled, all RRM features are implemented locally on each controller. RF Grouping is enabled by default and the MAC addresses of other WLCs in the same RF Group are listed to the right of the Group Mode checkbox.
Group Update Interval The group update interval value indicates how often the RF Grouping algorithm is run. This is a display-only field and cannot be modified.
Group Leader This field displays the MAC Address of the WLC that is currently the RF Group Leader. Because RF Grouping is performed per-AP, per-radio, this value can be different for the 802.11a and 802.11b/g networks.
Is this controller a Group Leader When the controller is the RF Group Leader, the value of this field is yes. If the WLC is not the leader, the previous field indicates which WLC in the group is the leader.
Last Group Update The RF Grouping algorithm runs every 600 seconds (ten minutes). This field only indicates the time (in seconds) since the algorithm last ran and not necessarily the last time a new RF Group Leader was elected.
Hope this helps!
Rob
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