Despite the many proposals for data center network (DCN) architectures, designing a DCN remains challenging. DCN design is especially difficult when expanding an existing network, because traditional DCN design places strict constraints on the topology (e.g., a fat-tree). Recent advances in routing protocols allow data center servers to fully utilize arbitrary networks, so there is no need to require restricted, regular topologies in the data center. Therefore, we propose a data center network design framework, that we call REWIRE, to design networks using an optimization algorithm. Our algorithm finds a network with maximal bisection bandwidth and minimal end-to-end latency while meeting user-defined constraints and accurately modeling the predicted cost of the network. We evaluate REWIRE on a wide range of inputs and find that it significantly outperforms previous solutions-its network designs have up to 100-500% more bisection bandwidth and less end-to-end network latency than equivalent-cost DCNs built with best practices.

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We study whether taxi companies can simultaneously save petroleum and money by transitioning to electric vehicles. We propose a process to compute the return on investment (ROI) of transitioning a taxi corporation's fleet to electric vehicles. We use Bayesian data analysis to infer the revenue changes associated with the transition. We do not make any assumptions about the vehicles' mobility patterns; instead, we use a time-series of GPS coordinates of the company's existing petroleum-based vehicles to derive our conclusions.As a case study, we apply our process to a major taxi corporation, Yellow Cab San Francisco (YCSF). Using current prices, we find that transitioning their fleet to battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs) is profitable for the company. Furthermore, given that gasoline prices in San Francisco are only 5.4% higher than the rest of the United States, but electricity prices are 75% higher; taxi companies with similar practices and mobility patterns in other cities are likely to profit more than YCSF by transitioning to EVs.

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