In mobile devices, the wireless network interface card (WNIC) consumes a significant portion of overall system energy. One way to reduce energy consumed by a device is to transition its WNIC to a lower-power sleep mode when data is not being received or transmitted.

This talk discusses client-centered techniques for saving energy during TCP downloads. The basic idea is that the client predicts when packets will arrive, keeping the WNIC in sleep mode only when necessary. Furthermore, the client increases the amount of time that can be spent in sleep mode by shaping the traffic; in particular, the client convinces the server to send data in bursts rather in a smooth manner, trading lower WNIC energy cost for increased transmission time. Our technique uses client-side modifications to TCP and does not rely on any assistance from the server, a proxy, or IEEE 802.11b power-saving mode. Initial results show that while there is a modest increase in the transmission time, our scheme can save significant WNIC energy.