If Enable QoS checkbox is selected, choose a default DSCP mark to automatically mark incoming traffic without reference to a particular classifier. Click 'Apply/Save' button to save it.
Usage Notes:
If the Enable QoS checkbox is not selected, all QoS will be disabled for all interfaces.
The default DSCP mark is used to mark all egress packets that do not match any classification rules.
QoS and a non-default queue are highly recommended for PPP WAN services. Each time a PPP WAN service starts or resets, if a non-default queue does not exist, one will be created and QoS automatically enabled.