Classification for uplinks and downlinks in QoS

Uplink and downlink ports can be configured for ingress traffic classification based on the values of dot1p or DSCP or both in the Ethernet and IP headers respectively.

Dot1p: A 3-bit field called the Priority Code Point (PCP) within an Ethernet frame header when using VLAN tagged frames as defined by IEEE 802.1Q. Eight different classes of service are available as expressed through the 3-bit PCP field.
DSCP: Differentiated Services Code Point (DSCP) is a field in an IP packet that enables different levels of service to be assigned to network traffic.
DSCP and Dot1p: For IP traffic use DSCP, and for non-IP traffic use dot1p priority.

For an end-to-end QoS, all the hops along the way must be configured with similar QoS policies of classification and traffic management.

In an end-to-end QoS policy, the traffic prioritization provides the following benefits:

Greater bandwidth ensures higher priority for the associated traffic at the queue. At the interconnect, the packets are egressed based on the associated queue bandwidth.
Egress dot1p remarking helps to achieve priority at the next hops in the network. If the queue egress traffic is remarked to a dot1p value, and that dot1p value is mapped to a queue in the next hops with higher bandwidth, then the packets in the end-to-end network are treated with higher priority.