This is the index of the Class-of-Service profile applied to this co-routed tunnel, governing priority and shaping for both the forward and reverse legs of the bidirectional circuit uniformly. An admin cross-references this index against the CoS profile table to confirm the intended priority treatment applies to the whole circuit, not just one direction. For example, a CoS profile index of 2 tied to a strict-priority profile ensures both the send and return paths of this circuit get consistent low-latency treatment.