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A High Performance Hybrid ToR for Data Centers


The potential advantages of optics at high link speeds have led to significant interest in deploying optical switching technology in data-center networks. Initial efforts have focused on hybrid approaches that rely on millisecond-scale circuit switching in the core of the network, while maintaining the flexibility of electrical packet switching at the edge. Recent demonstrations of microsecond-scale optical circuit switches motivate considering circuit switching for more dynamic traffic such as that generated from a top-of-rack (ToR) switch. Based on these technology trends, this dissertation presents a prototype hybrid ToR design called REACToR. REACToR combines 10-Gbps packet switching and 100- Gbps circuit switching, and appears to end-hosts as a 100-Gbps packet-switched ToR. REACToR synchronizes end host transmissions with end-to-end circuit assignments, and can react to rapid, bursty changes in the traffic from end hosts on a time scale of 100s of microseconds. To service data center traffic demands effectively, REACToR needs to schedule the heavy bandwidth-hungry flows to the circuit switching network, and the small latency-sensitive flows to the packet switching network. To address this problem, this dissertation also presents a new switch scheduling algorithm called Solstice. Solstice minimizes the frequency of circuit reconfigurations to maximize circuit utilization when reconfiguration delay is not negligible. Evaluations also show that it can schedule data center traffic workloads effectively with practical computational overheads. As a result, when using a REACToR hybrid switch with the Solstice scheduling algorithm, optical circuit switching extends to layers even closer to end hosts. Combined with a lower-provisioned electrical packet switch, the hybrid architecture services data center workloads with almost full bi-sectional bandwidth of high link rates like 100Gb/s. It provides network performance comparable to a full fat-tree that consists of electrical packet switches, but with much lower costs

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