Rethinking transfer optimization in a datacenter: Integrating load balancing with multipath flow control

The various flows in production datacenters usually can be classified into two types: bandwidth-hungry and delay-sensitive. To improve their performance, datacenter networks require effective load balancing and flow control protocols, respectively. However, as the two techniques are typically employed separately in current datacenters, they are unable to optimize the network in a coordinated way. In this work, we argue that the adaptive routing, in load balancing sense, and the flow control, in congestion control sense, could be tightly coupled at the transport layer to handle the complex datacenter traffic. We design OmniFlow, a novel transfer protocol which aims to achieve a proper balance between throughput and latency in a datacenter. Firstly, it can simultaneously and precisely measure the queueing latencies on multiple paths between two hosts, which enables it to have more visibility of the path congestion and have better control of the transmission states. Secondly, OmniFlow adaptively integrates the load balancing and flow control modules and shares the same congestion metrics (i.e. queueing latencies) between them. Based on different network conditions, it either dynamically reroutes flows to utilize the bisection bandwidth or proactively adjusts flow rates to bound queueing occupancies. The results of extensive experiments show that OmniFlow can provide both low average and tail latency for small flows without sacrificing the throughput of elephant flows.