Weighted fairness in buffered crossbar scheduling

The crossbar is the most popular packet switch architecture. By adding small buffers at the crosspoints, important advantages can be obtained: (1) crossbar scheduling is simplified; (2) high throughput is achievable; (3) weighted scheduling becomes feasible. We study the fairness properties of a buffered crossbar with weighted fair schedulers. We show by means of simulation that, under heavy demand, the system allocates throughput in a weighted max-min fair manner. We study the impact of the size of the crosspoint buffers in approximating the weighted max-min fair rates and we find that a small amount of buffering per crosspoint (3-8 cells) suffices for the maximum percentage discrepancy to fall below 5% for 32×32 switches.