Collector-based cell reordering in load-balanced switch fabrics

Abstract

Load-balanced switch fabrics offer the promise of very high capacity without the requirement of increased operating rates. We provide a novel solution to the well-known cell reordering problem, which arises in load-balanced switch fabrics if different paths through the switch fabric have different delays. We give a simple sorting circuit, easily implemented in hardware, that can be placed in the final stage of the fabric. This minimizes the delay through the fabric and removes any constraints on operation of the first stage. We show that the sorting circuit can be implemented to operate at a rate of one cell per cycle; we give a probabilistic analysis of required queue occupancies, both at the sorting circuit and at midstage elements; we also briefly discuss congestion control in load-balanced switch fabrics.