Final answer:
Time Division Multiple Access (TDMA) allows only one unit to transmit per timeslot and goes unused if that specific participant has no data to transmit.
Step-by-step explanation:
The JTIDS/MIDS access mode that allows only one unit to transmit per timeslot and goes unused if that specific participant has no data to transmit is Time Division Multiple Access (TDMA).
In TDMA, the available time slots are divided into fixed intervals, and each participating unit is assigned a specific time slot to transmit its data.
If a unit has no data to transmit during its assigned time slot, that slot remains unused. This ensures efficient use of the available bandwidth.