This is the inbound-direction counterpart to cpwVcMplsOutboundLsrXcIndex, pointing to the cross-connect entry in the MPLS-LSR-MIB representing the outer tunnel that delivers labeled traffic into this router for the pseudowire, reading zero when no outer tunnel is used. It's the object to follow when inbound traffic for a VC isn't arriving as expected and the suspicion is the underlying LDP or manually-configured LSP feeding it, rather than the VC label mapping itself. A cross-connect index here that no longer exists in the MPLS-LSR-MIB is a clear sign the inbound outer tunnel was removed while this pseudowire's configuration still references it.