Interface index of the coupling link. Note that only those ports can be chosen which do not belong to another L2 redundancy mechanism like ring redundancy or dual homing and that row creation is only done by writing to hmRingCplRowStatus.
Sources for this description
Belden, GarrettCom and Hirschmann IT official standalone MIBsHirschmann MIB copies (LibreNMS/Observium Community)Netdisco MIB archive copies