This is the specific index value used to look up the configured transport tunnel in whichever tunnel table -- cienaCesMplsTunnel for static MPLS tunnels or cienaCesGmplsTunnel for GMPLS tunnels -- corresponds to the tunnel type reported in the sibling ConfigTunnelType object. This index is what an SNMP tool would use to programmatically pull up the full tunnel details (path, bandwidth, state) underlying this specific pseudowire. Without cross-referencing this index against the correct tunnel table based on the type field, an admin could accidentally look up the wrong tunnel entirely if two tunnel types happen to share the same numeric index.