D-LQF: An Efficient Distributed Scheduling Algorithm for Input-Queued Switches

Due to the massive use of parallel and distributed operations of inputs and outputs, iterative scheduling algorithms are attractive in finding a maximal size matching for an input-queued switch. For constructing a large high-speed switch, a distributed multi-chip implementation of an iterative scheduling algorithm should be followed. Since different chips may locate on different switch linecards and linecards can be separated by tens of meters, the propagation delay between chips/linecards is non-negligible. This calls for a pipelined implementation of a single-iteration scheduling algorithm. In this paper, an efficient, pipelined single-iteration algorithm called Distributed Longest Queue First (D-LQF) is proposed. In D-LQF, exhaustive service policy is adopted for reusing the matched input-output pairs in the previous time slot. To avoid incorrectly granting an empty VOQ from transmission (caused by inter-chip latency), each output keeps track of the lengths of all VOQs destined to it. As compared with other single-iteration scheduling algorithms, extensive simulation results show that D-LQF provides the best delay-throughput performance.