The wmm mandatory enable disables STAs that do not support WMM from connecting to a WMM-enabled AP.
The undo wmm mandatory enable allows STAs that do not support WMM to connect to a WMM-enabled AP.
By default, STAs that do not support WMM are allowed to connect to a WMM-enabled AP.
On a WLAN, wireless channels are open and all STAs have the same chance to occupy a channel. You can configure WMM to distinguish high-priority packets and enable the high-priority packets to preempt channels. You can also disable STAs that do not support WMM from connecting to a WMM-enabled AP, which prevents those STAs from preempting channels of WMM-capable STAs.