Opportunistic Packet Forwarding for Proactive Transport in Datacenters
Date
2024-07-16
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Abstract
Proactive transport protocols in datacenters are designed to avoid congestion by regulating flow sending rates via credit allocation. However, when a new flow starts, it takes one Round-Trip Time (RTT) before credits can be assigned to the new flow. To avoid stalling flows, modern proactive protocols allow a new flow to blast a burst of unscheduled packets at line rate during the pre-credit phase. However, sending too many unscheduled packets could cause temporary traffic spikes that lead to queue build-ups, packet losses, and retransmissions, which are particularly detrimental to short flows. In this thesis, we present the design and evaluation of Opportunistic Packet Forwarding (OPF), a building block for proactive transports designed to minimize pre-credit packet losses with negligible overhead on network switches. The key idea in OPF is to allow pre-credit packets to opportunistically take detours to avoid congested links on the shortest paths, effectively trading off packet losses for slightly increased delay. We have implemented OPF using P4 switches and integrated our implementation with Homa and NDP. Our results on a range of traffic loads show significant improvement in the 99-th percentile of flow completion time for short flows, namely, up to 60% reduction in NDP and 50% in Homa.
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Software-Defined Networking, Programmable Switches, Datacenter Networks
Citation
Shani, A. (2024). Opportunistic packet forwarding for proactive transport in datacenters (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.