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Input-queued cell switches employing the oldest-cell-first (OCF) policy have been shown to yield low mean delay characteristics. Moreover, it has been proven that OCF is stable for admissible i.i.d. arrival traffic when executed with a scheduling speedup of 2. However, an increase in link rates and port densities directly leads to a decrease in packet duration times, to a point where cell-by-cell switching is no longer considered practical. To address this challenge, this paper studies frame-based scheduling algorithms for a scalable combined input-output queued (CIOQ) switch architecture. The latter is decomposed into independent subgroups, each employing multiple simple crosspoint switches. A key outcome of this decomposition is a substantial reduction of scheduling times. Unlike many other schemes, which necessitate custom integrated circuits, the architecture proposed here utilizes commercially available crosspoint switches. We present a Lyapunov-based stability analysis that dictates moderate conditions under which the switch is stable for all admissible traffic patterns. By reconfiguring the crossbar switch once every several time slots, the timing constraints imposed on the scheduling algorithm are significantly relaxed. Simulation results are presented, demonstrating the merits of the approach, particularly in the presence of bursty traffic scenarios.
Date of Conference: May 30 2007-June 1 2007