Thor: A Scalable Hybrid Switching Architecture for Data Centers

Optical interconnects are emerging as a high bandwidth and low energy alternative to traditional electrical networks. However, most exiting designs put optical switching in the core layer due to issues, including limited scalability, potential bottleneck of the control plane, and high cost of the multi-wavelength switch. To this end, we propose Thor, a hybrid network architecture using optical interconnects as the main load bearing portion. It employs the hypercube topology and multi-hop circuit switching to enable server-level optical access, thus solving the scalability and connectivity limitations. Then, in order to build a faster control plane operating short-lived circuits in a large scale, Thor uses a distributed control system over the electrical network, with a new path setup mechanism capable of establishing multiple optical circuits concurrently. Moreover, Thor employs a novel optical switch design to utilize multiple wavelengths more efficiently. Our evaluation results show that Thor consumes at least 59% and 6% less power than existing electrical and optical designs. For performance, Thor is able to deliver 90% bisection bandwidth of a non-blocking network and reduce the end-to-end latency significantly. Finally, by separately delivering mice and elephant flows, Thor achieves salient improvements in average flow completion times compared with existing approaches.