On the influence of selection function on the performance of fat-trees under hot-spot traffic

Fat-tree topology has drawn a considerable interest because it offers a rich connectivity among source and destination nodes. Routing in fat-trees is composed of a routing function and a selection function. The selection function was shown to have a great impact on the performance [2]. In this paper, we study the performance of fat-trees in case of hot-spot traffic. First, we propose a new selection function SAOP, which is based on the stage and the source node address. We argue that the SAOP is more suitable for hot-spot traffic than other selection functions. We show that the new selection function outperforms other well known selections functions under hot-spot traffic. Then, we compare a deterministic version of the SAOP to that of the adaptive one. We show that their performances are comparable. This guarantees an in-order packet delivery. Finally, we analyze the SAOP algorithm and show that the congestion occurs only within the parent switches of the destination which explain the outperforming results of the SAOP.