In this paper we consider an SS/TDMA system with uplink beams and downlink beams, where uplink beam has bandwidth βiand downlink beam has bandwidth αj. The maximum traffic which can be handled by the satellite (in any given time slot) is assumed to be . Multiplexing and demuitiplexing are also assumed. An optimal time slot assignment algorithm to minimize the total transmission time for any given traffic demand matrix is proposed and analyzed. Other system configurations of interest are also discussed.