High-speed switch scheduling for local-area networks
ACM Transactions on Computer Systems (TOCS)
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Modern switches and switching fabrics typically employ virtual output queues (VOQs) at network adapters, in order to mitigate head-of-line blocking. The core of the switch, often a crossbar, can either be bufferless or buffered. Previous research on random arbitration for bufferless crossbars found that the throughput for large switch sizes is bounded at 63% [1]. Although crossbars containing crosspoint buffers are shown to reach 100% throughput under uniform traffic, their scalability is restricted by the quadratic growth of the number of crosspoint buffers, and the size of each, which depends on the intra-switch (VOQ-crossbar) round trip time (RTT). In this paper, we study an alternative architecture [2], which can reduce buffer requirements, by (a) having a linear growth of the number of buffers, and (b) making the size of each independent of the RTT. As the scheduler in such an architecture may match multiple inputs to the same output at the same time, we refer to such matchings as approximate, as opposed to the exact matchings required in bufferless crossbars.