In this paper we consider an SS/TDMA system with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> uplink beams, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> downlink beams, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</tex> connection points. We first assume that the downlink is α times faster than the uplink, and a simple time multiplexing scheme is employed. An optimal time slot assignment algorithm for any <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M, N,\alpha</tex> , and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</tex> , <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 \leq K \leq \min (M, \alphaN)</tex> , and for any traffic matrix is presented, where optimality means achieving the minimal possible total transmission time for the given traffic matrix. The number of switching matrices generated by the algorithm never exceeds <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MN + K\alpha + 1</tex> . Extensive simulation results on randomly generated matrices are carried out, showing that the average number of switching matrices generated is substantially lower than the upper bound. The case when the uplink is faster than the downlink is also considered.