The Crosspoint-Queued Switch

This paper calls for rethinking packet-switch architectures by cutting all dependencies between the switch fabric and the linecards. Most single-stage packet-switch architectures rely on an instantaneous communication between the switch fabric and the linecards. Today, however, this assumption is breaking down, because effective propagation times are too high and keep increasing with the line rates. In this paper, we argue for a self-sufficient switch fabric by moving all the buffering from the linecards to the switch fabric. We introduce the crosspoint-queued (CQ) switch, a new buffered-crossbar switch architecture with large crosspoint buffers and no input queues, and show how it can be readily implemented in a single SRAM-based chip using current technology. For a crosspoint buffer size of one, we provide a closed-form throughput formula for all work-conserving schedules under uniform Bernoulli i.i.d. arrivals. Furthermore, we study the performance of the switch for larger buffer sizes and show that it nearly behaves as an ideal output-queued switch. Finally, we confirm our results using synthetic as well as trace-based simulations.