The configuration of QoS in the 3850 line has been improved due to its implementation of MQC (universal QoS configuration model) configuration instead of the old MLS QoS (platform-dependent QoS configuration) commands from the cisco 3750 and 3560 lines of switches. The main differences are highlighted in this table:
Support MLS QoS Support some of MQC at ingress
Does not support MLS QoS Support MQC [class-map, policy-map]
Support MLS QoS config and some of MQC CLI at ingress
It is important to recognize the main fundamental change in the QoS approach.
On the 3750, by default the QoS is disabled whereas on the 3850, it is enabled. Also in order to preserve Layer 2 (L2)/Layer 3 (L3) QoS marking on the 3750 platform, a trust configuration must be applied.
In the case of the cisco 3850 series switchs , all packets by default are trusted (the L2/L3 QoS marking is preserved), unless you change it with an application of a specific policy map on the ingress or egress interface.