Networking @Scale Summer 2022
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Improving Transfer Times in the Backbone Network Using QUIC Jump Start | Joseph Beshay

Transfers in high-BDP links incur a startup delay for congestion control to probe the bandwidth of the underlying link. The impact of this delay is inversely proportional to the size of the transfer since small transfers may repeatedly spend all their transfer time probing for the available bandwidth and never reach it or utilize it. While this is necessary for links with rapidly changing capacity, it can be avoided in more predictable links such as backbone links. Existing TCP approaches are either limited to specific pairs of endpoints or require intermediate proxies. In this presentation, we share the approach we’ve developed for use with QUIC deployments in Meta’s backbone network. We use a modified congestion controller that tracks the average congestion control state for connections using each backbone path. This state is then used to “jumpstart” new connections across the same path, significantly reducing the startup delay. This, coupled with QUIC 0-rtt, offers significant savings compared to existing TCP-based approaches for transfers of size close to the path BDP.

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