This INTEGER decides the actual mechanism used to resolve this sub-port's incoming CoS: pinning everything to one fixed value, deriving it from an 802.1p tag at one of two possible positions in a Q-in-Q stack, or deriving it from DSCP. Picking the wrong option for a given customer's traffic, for example dscpToRcos on traffic that never sets DSCP, means all their traffic silently resolves to a default, low RCoS instead of its intended priority. Choosing dot1dToRcosTag2 for a customer whose relevant 802.1p priority sits on the inner, second, VLAN tag in a Q-in-Q setup rather than the outer tag is a real configuration decision this object controls.