This is the administrative up/down state of an OMS interface, defaulting to up, letting an operator deliberately enable or disable that multiplex section independent of its actual operational health. An admin would set this down before performing planned work that affects every wavelength riding that OMS, since taking it down is a much bigger action than disabling a single channel. Because OMS carries many wavelengths at once, accidentally leaving this at down after maintenance would silently block every service on that multiplex section.