Delphi: A Software Controller for Mobile Network Selection

This paper presents Delphi, a mobile software controller that helps applications select the best network among available choices for their data transfers. Delphi optimizes a specified objective such as transfer completion time, or energy per byte transferred, or the monetary cost of a transfer. It has four components: a performance predictor that uses features gathered by a network monitor, and a traffic profiler to estimate transfer sizes near the start of a transfer, all fed into a network selector that uses the prediction and transfer size estimate to optimize an objective. For each transfer, Delphi either recommends the “best” single network to use, or recommends Multi-Path TCP (MPTCP), but crucially selects the network for MPTCP’s “primary subflow”. The choice of primary subflow has a strong impact on the transfer completion time, especially for short transfers. We designed and implemented Delphi in Linux. It requires no application modifications. Our evaluation shows that Delphi reduces application network transfer time by 46% for Web browsing and by 49% for video streaming, compared with Android’s default policy of always using Wi-Fi when it is available. Delphi can also be configured to achieve high throughput while being battery-efficient: in this configuration, it achieves 1.9x the throughput of Android’s default policy while only consuming 6% more energy.