Preserving QoS in outbound traffic in a VLAN
QoS is implemented in the form of rules or policies that are configured on the switch. Although you can use QoS to prioritize traffic only while it moves through the switch, you derive the maximum benefit by using QoS in an 802.1Q VLAN environment (with 802.1p priority tags) or in an untagged VLAN environment (with DSCP policies in which QoS sets priorities that downstream devices can support without reclassifying the traffic).