The Sticky Client Problem:
A client is referred as “Sticky” when it does not roam or move to a nearby AP connection that has stronger signal strength. As illustrated in the above figure, when Optimized Roaming is disabled, the client will continue to stay with the AP at very weak signal strength, for example—lower than -86 dB. Lower signal strength will lead to increase in Airtime interference, thus reducing the overall performance.
Solution—Cisco Optimized Roaming:
Cisco Optimized Roaming addresses the sticky client challenge by pro-actively disconnecting clients, thus enabling the clients to move to a nearby AP that offers stronger connectivity. It achieves this functionality by actively monitoring Data RSSI packets, and enforcing client disassociation when the RSSI is lower than the set threshold. As illustrated in the above figure, when Optimized Roaming is enabled, the clients with signal strength lower than -80 dB will receive disassociation and achieves the following:
- Client receives best connectivity and maintains the quality of experience.
- Improves overall performance of each AP cell by reducing Airtime interference.
The client will be allowed to rejoin the AP when the client RSSI value has increased to 6 dBm above the disassociation threshold. For example, if the Data RSSI threshold is -80 dBm, the client will be allowed to re-associate once the RSSI values is increased to -74 dBm.
|Enabling Optimized Roaming
||Optimized Roaming is disabled by default. It can be enabled per band, meaning it can be enabled on b/g/n, a/ac/n, or both.
|Setting the Optimized Roaming threshold parameters
||The Optimized Roaming thresholds are shared with the coverage hold detection thresholds.Here is a description of the three fields used for Optimized Roaming:
- Data RSSI value – This is the threshold value to determine if a data packets RSSI value is too low. Packets received at or below this value are considered below the optimized roaming threshold.
- Coverage Exception Level Percentage – This marks the percentage of data packets that can be received below the Data RSSI value. If this percentage exceeds, the client will be disassociated.
- Number of Data Packets Received – This is the minimum number of packets that must be received to trigger a client disassociation.
By default, the data RSSI value is set to -80 dBm, the coverage exception level is 25%, and the default number of packets is 50.
So by default, if Optimized Roaming is enabled and more than 25% of at least 50 packets in a 5 second period is less than -80 Data RSSI, the AP will disassociate the client once the reporting interval of 90 seconds expires.
|-80 dBm / 25% / 50 Packets
|Optimized Roaming Interval
||The time interval at which the AP reports the client statistics. This value is defaulted to 90 seconds
|Optimized Roaming Data Rate Threshold
||The goal of the Optimized Roaming feature is only to affect clients that are connected on legacy data rates. These are the clients that are using a majority of the Airtime.
This value applies the Optimized Roaming feature to clients connected at this data rate or lower. By default this is disabled, meaning Optimized Roaming is applied to all clients.