AccelToR: Accelerating TCP for Circuit/Packet Hybrid Data Centers With Packet Scheduling

To overcome the inherent limitation of the optical circuit switch (OCS) while utilizing its high bandwidth, circuit/packet hybrid networks are widely proposed for modern data centers. However, as today’s OCS has reduced the reconfiguration delay to microseconds, the circuit from a source rack to a destination rack typically lasts fewer than 10 RTTs. Such a short circuit time brings a critical challenge to TCP, as it is difficult for a TCP sender to sufficiently grow its congestion window (CWND) and utilize the optical bandwidth. To address this problem, in this work, we present <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AccelToR</i>, a top-of-rack switch for improving TCP performance in circuit/packet hybrid data center networks. AccelToR leverages end-host congestion control to “accelerate” a blocked TCP flow by temporarily scheduling its packets to be transferred through the packet network a few RTTs before its circuit is established, and after enlarging the flow’s CWND with the acceleration, the switch buffers the last window of packets. During the circuit time, the switch sends out the buffered packets, and the accelerated flows, which have their CWNDs already grown large, continue to send packets at high rates to achieve a high optical bandwidth utilization. Experiment results show that AccelToR achieves high throughputs for elephant flows and utilizes over <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbf {90\%}$ </tex-math></inline-formula> of the optical bandwidth, and it preserves short flow completion times for mice flows at the same time. In addition, AccelToR is robust under unexpected packet losses, and can benefit a wide range of TCP congestion control algorithms.