The algorithms implemented in LCOS ensure that the APS are intelligently distributed between the individual WLCs. This allows the APs to equally distribute the network load between all of the WLCs in a cluster, or to select an alternative WLC if one should fail. For this, an AP first sends out a discovery request on the network to identify all available WLCs. The WLCs then respond with a discovery response which an AP uses to create a prioritized list of WLCs. This AP prioritizes the list based on various criteria.
An AP works through the different criteria sequentially: If multiple WLCs appear to be ideal candidates after applying a criterion, the AP uses the next criteria to prioritize. This process ends when a WLC finally identifies just one WLC as being ideal after the prioritization described in the following.
Criteria for prioritization
- Specificity of the AP configuration: An AP evaluates whether a WLC can provide it with a configuration, and whether this contains a specific AP profile or a default profile. The AP prioritizes a specific AP profile as highest, followed by a default profile. If a profile is missing, it is given the lowest priority.
- The preference value: The AP evaluates the preference value that you have assigned to a WLC. The higher the number between 0 and 255, the higher the AP prioritizes the WLC.
If there still remain several WLCs which are considered to be ideal, the prioritization process continues by evaluating the connection status and the type of selection process (automatically vs. manually initiated):
- When the calculation is triggered for the first time, an AP calculates a weighted value for each of the remaining WLCs by taking the number of APs connected to each WLC and comparing this with the maximum possible number of APs (license usage). Ultimately, the ideal WLC is taken as that with the lowest license usage.
Note: If a WLC has reached the maximum possible number of AP connections (license quota exhausted), an AP no longer considers the affected WLC for the current selection.
- In the case of automatic checking of the ideal AP distribution, an AP stays with the WLC it is connected to if this WLC is included in the list of the remaining WLCs. Otherwise, a randomized algorithm causes the AP to select an arbitrary AP.
- In the case of a manually triggered check, a randomized algorithm ensures that the APs distribute the available license quotas as evenly as possible across the network.
