One-way satmodems (DVB-IP modems ) use a return channel not based on communication with the satellite, such as telephone or cable.
Two-way satmodems (DVB-RCS modems, also called astromodems) employ a satellite-based return channel as well; they do not need another connection. DVB-RCS is ETSIstandardEN 301 790.
... plus water plus light (energy) yields oxygen plus sugar. In animal bodies, this is exactly reversed: oxygen plus sugar yields carbon dioxide plus water plus energy. ...