Randomized scheduling algorithms for high-aggregate bandwidth switches

Abstract

The aggregate bandwidth of a switch is its port count multiplied by its operating line rate. We consider switches with high-aggregate bandwidths; for example, a 30-port switch operating at 40 Gb/s or a 1000-port switch operating at 1 Gb/s. Designing high-performance schedulers for such switches with input queues is a challenging problem for the following reasons: 1) high performance requires finding good matchings; 2) good matchings take time to find; and 3) in high-aggregate bandwidth switches there is either too little time (due to high line rates) or there is too much work to do (due to a high port count). We exploit the following features of the switching problem to devise simple-to-implement, high-performance schedulers for highaggregate bandwidth switches: 1) the state of the switch (carried in the lengths of its queues) changes slowly with time, implying that heavy matchings will likely stay heavy over a period of time and 2) observing arriving packets will convey useful information about the state of the switch. The above features are exploited using hardware parallelism and randomization to yield three scheduling algorithms-APSARA, LAURA, and SERENA. These algorithms are shown to achieve 100% throughput and simulations show that their delay performance is quite close to that of the maximum weight matching, even when the traffic is correlated. We also consider the stability property of these algorithms under generic admissible traffic using the fluid-model technique. The main contribution of this paper is a suite of simple to implement, high-performance scheduling algorithms for input-queued switches. We exploit a novel operation, called MERGE, which combines the edges of two matchings to produce a heavier match, and study of the properties of this operation via simulations and theory. The stability proof of the randomized algorithms we present involves a derandomization procedure and uses methods which may have wider applicability.

Frame-aggregated concurrent matching switch

“…In particular, it was shown that a class of stable randomized matching algorithms [6,7] with O(N ) operations can be amortized to O(1) time complexity using only sequential hardware and local state information at each linecard.…”

Distributed Cross-Layer Algorithms for the Optimal Control of Multihop Wireless Networks

“…In [42], Tassiulas showed that randomized algorithms can be used to achieve maximum throughput in input queued switches with linear computational complexity. To improve the exponentially high delay performance of [42], [19] introduced randomized algorithms for switches. Other research, for example, [24], [36], [39], [32], [1], [16], [37], [38], have contributed to the analysis of centralized throughput optimal policies in wireless networks.…”

Concatenating Packets in Variable-Length Input-Queued Packet Switches with Cell-Based and Packet-Based Scheduling

“…A class of matching algorithms based on randomized selection has been proposed to achieve high throughput [14], [15] with low computation complexity. These randomized schemes keep the matches that are likely to continue sending cells.…”