Hi
As for the attached design, how to start and what to consider as am a little bit confused, also on which Nodes/interfaces should I implement QoS, shall I do it for the upstream and downstream traffic?----------------source to destination both directions , qos only really comes into effect on congested sections of the network but its best practice to apply it end -end
3850s do not support MLS qos only Auto Qos and they trust DSCP by default too if you don't apply anything
this is how its applied at access port level , it will automatically generates class-maps as per doc depending what way you configure the access port
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/qos/configuration_guide/b_qos_3se_3850_cg/b_qos_3se_3850_cg_chapter_0100.html#reference_1F1A3B686CE64AACB5CC3B343D01B735
3750 - you can just add mls qos globally and then on access ports and trunks apply mls qos trust dscp , if your end devices phones only support cos use on access ports mls qos trus cos and make sure the mapping is correct in global config should be this will be auto-generated ----mls qos map cos-dscp 0 8 16 24 32 46 48 56
the class-maps you have built can go on wan interface as that's MQC layer 3 qos , MLS and Auto Qos is layer 2
I cant get your jpg to open so I cant see overall design , wan interfaces are usually done first then do layer 2 qos
