Minimizing Energy for Wireless Web Access with Bounded Slowdown

On many battery-powered mobile computing devices, the wireless network is a significant contributor to the total energy consumption. In this paper, we investigate the interaction between energy-saving protocols and TCP performance for Web-like transfers. We show that the popular IEEE 802.11 power-saving mode (PSM), a static protocol, can harm performance by increasing fast round trip times (RTTs) to 100 ms; and that under typical Web browsing workloads, current implementations will unnecessarily spend energy waking up during long idle periods. To overcome these problems, we present the Bounded-Slowdown (BSD) protocol, a PSM that dynamically adapts to network activity. BSD is an optimal solution to the problem of minimizing energy consumption while guaranteeing that a connections RTT does not increase by more than a factor p over its base RTT, where p is a protocol parameter that exposes the trade-off between minimizing energy and reducing latency. We present several trace-driven simulation results that show that, compared to a static PSM, the Bounded-Slowdown protocol reduces average Web page retrieval times by 5–64%, while simultaneously reducing energy consumption by 1–14% (and by 13× compared to no power management).