The aircraft (primarily the Satelite Data Unit) requires the geo position, the azimuth and eleveation of the aircraft (typically this is obtained from an INU/IRU or ADIRU) so that the beam steering unit (or in the case of a mechanically steered system, the antenna control unit) can line up on the available comsats at any given time. Airline usage policy etc is stored in the ORT (Owner Requirements Table) programmed into the SDU.
Hope this helps.
Dude
