This object specifies the list of interfaces to which R-APS service can be extended, without actually running R-APS. An interface identified in this fsErpsRingPort1SubPortList is the first port of a ring pair. This list is configured as SubPorts for fsErpsRingPort1. Whenever any state change is identified in fsErpsRingPort1, it is propogated to the list of interfaces identified by this MIB object. This object should be configured as IfIndex'1', IfIndex'2', ... IfIndex'n' where IfIndex'1', IfIndex'2', IfIndex'n' corresponds to an interface with valid interface ID. If IfIndex'n' in this list is the first port of the ring, then the second port of ring has to be identified as IfIndex'n' in fsErpsRingPort2SubPortList, where 'n' corresponds to the position of the interface index in the list. This object is currently applicable only when the fsErpsRingServiceType is set to mplsLSPPW. The administrator must ensure that the Pseudowire interfaces configured belong to the same LSP.