A system and method for communicating with an Internet Of Things (IoT) device via a satellite link. The method includes assigning a transmission mode to a physical channel, where the physical channel supports multiple timeslot durations and the transmission mode is selected from a single user (SU) or a multi-user (MU); selecting a timeslot duration from the multiple durations for a payload; obtaining, when the transmission mode is SU, a timeslot grant for use of the physical channel for the timeslot duration; and transmitting a burst including the payload, where the burst is transmitted synchronized with the timeslot grant when the transmission mode is SU and the burst is transmitted without synchronization when the transmission mode is MU.