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Stanford University Networking Seminar


Nandita Dukkipati (Google)
TIMELY: RTT-based Congestion Control for the Datacenter

12:15pm, Thursday, December 03 2015
Gates 104

About the Talk

Datacenter transports aim to deliver low latency messaging together with high throughput. We show that simple packet delay, measured as round-trip times at hosts, is an effective congestion signal in datacenters. First, we show that advances in NIC hardware have made RTT measurement possible with microsecond accuracy, and that these RTTs are sufficient to estimate switch queueing. Then we describe how TIMELY can adjust transmission rates using RTT gradients to keep packet latency low while delivering high bandwidth. We implement our design in host software running over NICs with OS-bypass capabilities. We show using experiments with up to hundreds of machines on a Clos network topology that it provides excellent performance: turning on TIMELY for OS-bypass messaging over a fabric with PFC lowers 99 percentile tail latency by 9X while maintaining near line-rate throughput. To the best of our knowledge, TIMELY is the first delay-based congestion control protocol for use in the datacenter, and it achieves its results despite having an order of magnitude fewer RTT signals (due to NIC offload) than earlier delay-based schemes such as Vegas.

This talk is based on a SIGCOMM 2015 publication.

About the Speaker

Nandita Dukkipati is a Senior Staff Software Engineer at Google, where she works on problems related to congestion management in large scale networks and servers. Nandita holds a Ph.D. in Electrical Engineering from Stanford University (2008).