1. Start Extreme Management Center.
2. Change to the Alarm and Events tab.
3. Click the Add button to the upper left.
4. Select Threshold alarm
5. Provide a name for the alarm
6. Change the Threshold type to Extreme Management.
7. Change Select Type to Wireless - AP
8. Change Statistics Name to AP Associated clients(MUs)
9 Change the Cross when Values to the appropriate values.
10. Select the Rearm when value goes below to get this to trigger again if limit is crossed.
11. Change to the Actions tab and select the action that you would like to take when this alarm is triggered.
12. Place a check in the Enabled check box.
13. Click the Save button.
Please note that you will need to enable stats collection on the wireless controller in order to gather these values.