HCF: a starvation-free practical algorithm for maximizing throughput in input-queued switches

Using virtual output queueing (VOQ), maximum matching scheduling algorithms have been shown to achieve 100% throughput in input-queued switches, but has high complexity such that implementation is infeasible for high-speed systems. Iterative maximal matching algorithms, proposed as an alternative, cannot run for more than a few iterations due to the hardware complexity involved, thus resulting in low throughput. In this paper, we introduce a starvation-free iterative maximal matching algorithm called highest count first (iHCF). The iHCF algorithm gives preferential service based on the approximate age of the head-of-line cell in a VOQ and maximizes the size of the matching using round-robin priority pointers. We show that iHCF can achieve 100% throughput under i.i.d and uniform traffic in a single iteration. We also show using simulations that it performs as well as other known practical algorithms and achieves 100% throughput when run for only a few iterations under different admissible traffic patterns. Compared to other algorithms, iHCF leads to low complexity architecture such that the scheduling does not become the bottleneck.