Issue No. 04 - April (2008 vol. 19)
Fairness in traffic management can improve the isolation between traffic streams, offer a more predictable performance, eliminate transient bottlenecks, mitigate the effect of certain kinds of denial-of-service attacks, and serve as a critical component of a quality-of-service strategy to achieve certain guaranteed services such as delay bounds and minimum bandwidths. In this paper, we choose a popular notion of fairness called max-min fairness and provide a rigorous definition in the context of input-queued switches. We show that being fair at the output ports alone, or at the input ports alone, or even at both input and output ports, does not actually achieve overall max-min fair allocation of bandwidth in a switch. Instead, we propose a new algorithm that computes the exact max-min fair allocation of rates for the flows through the switch. In addition to proving the correctness of the algorithm, we show that it can be implemented in a distributed fashion at the input and output ports to determine the max-min fair rates. We further propose a practical scheduling strategy based on our algorithm and present simulation results, using both real traffic traces as well synthetic traffic, to evaluate the fairness of a variety of popular scheduling algorithms for input-queued switches. The results show that our scheduling strategy achieves better fairness than other known algorithms for input-queued switches and, in addition, achieves throughput performance very close to that of the best schedulers.
Routers, input-queued switches, fairness, quality-of-service
H. Sethu and M. Hosaagrahara, "Max-Min Fair Scheduling in Input-Queued Switches," in IEEE Transactions on Parallel & Distributed Systems, vol. 19, no. , pp. 462-475, 2007.