This classifies what kind of underlying service a CFM maintenance association is monitoring (mplsVs, ethVs, vlan, pbtTunnel, and other listed types), and it directly changes how the companion cienaCesCfmServiceValue field should be interpreted, since that field's meaning is entirely dependent on this type. An admin must read this field before making sense of ServiceValue at all, and this pair together must be unique per row, meaning the same combination can't be reused to monitor two different underlying entities. For example, cienaCesCfmServiceType = vlan(3) means the accompanying ServiceValue holds a VLAN ID, whereas the same field set to pbtTunnel(4) would mean ServiceValue instead identifies a PBB-TE tunnel, a completely different kind of reference.