AMP: An Adaptive Multipath TCP for Data Center Networks

MPTCP and its ECN-capable variants such as XMP and DCM have recently been introduced to effectively exploit the path diversity of modern data center networks (DCNs). Although these multipath schemes improve overall network throughput compared to single-path schemes due to their fast, host-based, load balancing ability, they failed to address the following two problems: TCP incast and last hop unfairness. Firstly, these mechanisms cause frequent TCP incast collapses when used for workloads with a many-to-one communication pattern, commonly found in DCNs. Secondly, the last hop unfairness problem severely violates network fairness as single-path flows achieve 2-5 times less throughput than multipath flows. To effectively tackle these problems, we propose the Adaptive MultiPath (AMP) congestion control mechanism that quickly detects the onset of these problems and transforms its multipath flow into a single-path flow. Once these problems disappear, AMP safely reverses this transformation and continues data transmission via multiple paths. Our evaluation results under a diverse set of scenarios in a large-scale fat-tree topology demonstrate that AMP is robust to the TCP incast problem and improves network fairness between multipath and single-path flows significantly with no performance loss.