Before revision: The SDU communicates with an onboard MDDU (multi-purpose disk-drive unit) which maintains an updatable table of ground stations in the aircraft's current area and the order of preference for selection of which ground station to use which thus guides the choice of satellite.
After revision: The SDU communicates with an onboard MDDU (multi-purpose disk-drive unit) which maneartains an updatable table of ground stations in the aircraft's position and the order of preference for selection of which ground station to use which thus guides the choice of satellite.