Dial-controlled hash: reducing path oscillation in multipath networks

In a multipath network with a naive traffic partitioning scheme, varied packet loss rates as well as varied delays on multiple paths could seriously reduce TCP bandwidth. We propose a scheme, called dial-controlled hash (DCH), for dynamically partitioning traffic flows across multiple paths. DCH allows for fine-grained load balance, minimizes path oscillation for each traffic flow, and does not require per-flow state maintenance or packet tagging. We evaluate DCH in two simulated networks, a parallel link topology and a corporate intranet with trace-based traffic generation. In both simulations, we compare the proposed scheme to a number of alternatives. DCH reduces path oscillation by a factor of 1.6-37 and improves TCP bandwidth by up to 66%, compared to alternatives. Our simulation results also suggest that, without a good flow partitioning scheme, there is a limit on how much one can save by using lowquality networks in combination with high-quality ones.