3750/3560 platform ASIC only supports statistics on a
per dscp basis rather than on a per traffic class basis, so we cannot
support the
CISCO-CLASS-BASED-QoS-MIB on those platforms. There is a plan to use the CISCO-Port-QoS-MIB in the future.
There is actually a defect for this request to add the feature for Port-QoS MIB :
CSCsy18409 CISCO-PORT-QOS-MIB packet & octet counters are not supported in 3750