Guaranteed scheduling for switches with configuration overhead
In this paper we present three algorithms that provide performance guarantees for scheduling switches, such as optical switches, with configuration overhead. Each algorithm emulates an unconstrained (zero overhead) switch by accumulating a batch of configuration requests and generating a corresponding schedule for a constrained switch. Speedup is required both to cover the configuration overhead of the switch and to compensate for empty slots left by the scheduling algorithm. Scheduling algorithms are characterized by the number of configurations, Ns, they require to cover a batch of requests, and the speedup required to compensate for empty slots, Smin. We show that a well known exact matching algorithm, EXACT, leaves no empty slots (i.e. Smin = 1), but requires Ns ≈ N2 configurations for an N-port switch leading to high overhead or large batches and hence high delay. We present two new algorithms that reduce the number of configurations required substantially. MIN covers a batch of requests in the minimum possible number of configurations, Ns = N, but at the expense of many empty slots, Smin ≈ 4 log2N. DOUBLE strikes a balance, requiring twice as many configurations, Ns = 2N, while reducing the number of empty slots so that Smin = 2. We show that DOUBLE offers the lowest required speedup to emulate an unconstrained switch across a wide range of port count and delay.
