A Time-Division Multiplexed (TDM) Hierarchical Switching System (HSS), proposed by Eng and Acampora [5], provides any size of bandwidth for a number of subscribers by allocating proper number of time-slots in a frame. In this paper, we present a binary time-slot assignment (TSA) algorithm by which a proper size of time-slots in the frame are allocated to each subscriber so as to meet its bandwidth requests. The time complexity of the proposed algorithm is O(NLlog2 L) in which N is the number of input/output links of the central switch and L is the number of time-slots allotted to each link in the frame. As the authors know, the most efficient algorithm proposed in the literature has time complexity of O(min(L, M2)min(N, M)M2), in which M is the number of subscribers that is larger than N in TDM/HSS system. To give a clear idea of relative efficiency between two algorithms, let us give a typical situation of M = L = O(N2). In this configuration our algorithm makes a significant improvement in time complexity by the order of O(M2/log2M).