LoCo: Localizing Congestion

Datacenter congestion control remains to be a hard problem. The challenge is that while congestion control is usually implemented at the end-hosts, congestion itself can happen at network switches. Thus, the ability of end-hosts to react to congestion is fundamentally limited by the timeliness and precision of congestion signals from the network. Unfortunately, despite decades of research, the community is still in quest of such timely and precise congestion signals. LoCo takes a new approach to resolving the congestion control problem: it localizes the congestion to egress queues of the end-hosts, precisely where congestion control is implemented, while bounding both the worst-case queuing at each switch and the network utilization. LoCo achieves this by exploiting the structure in datacenter network topologies to perform network-wide admission control for each and every packet in the network. LoCo is a clean-slate design that requires changes in network switches as well as end-hosts NICs. We evaluate LoCo using both an end-to-end hardware implementation and large-scale simulations; our results show that LoCo not only achieves the above mentioned theoretical guarantees, but also achieves better performance than several state-of-the-art congestion control protocols over standard datacenter workloads.