This identifies the specific instance of a queue group (since queue groups can be replicated per-port or per-slot) that a given MPLS Class Type is mapped to on this device. An admin needs this instance number, not just the group index, to locate the exact hardware queue on a specific line card or port when multiple copies of the same logical queue group exist across the chassis. For example, queue group index 12 instance 4 might correspond to that queue group as it exists specifically on slot 4, distinguishing it from the same index on other slots.