PABO: Congestion mitigation via packet bounce

Today's data center applications can generate a diverse mix of short and long flows. However, switches used in a typical data center network are usually shallow buffered in order to reduce queueing delay and deployment cost. As a result, the buildup of the queues by long flows can block short flows, leading to frequent packet losses and retransmissions, which translates to crucial performance degradation. While multiple end-to-end TCP-based solutions have been proposed, none of them have tackled the real challenge: reliable transmission in the network. In this paper, we fill this gap by presenting PABO — a novel link-layer design that can mitigate congestion by temporarily bouncing packets to upstream switches. PABO's design fulfills the following demands: i) providing per-flow based flow control on the link layer, ii) handling transient congestion without the intervention of end devices, and iii) gradually back propagating the congestion signal to the source when the network is not capable to handle the congestion. We complete a proof-of-concept implementation, and experiments under different severities of congestion show that PABO outperforms the standard unreliable link-layer protocol by guaranteeing zero packet loss while introducing only a reasonable stretch on packet delay.