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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 mobile device is to transition its WNIC to a lower-power sleep mode when data is not being received or transmitted. This paper investigates client-centered techniques for trading download time for energy savings during TCP downloads, in an attempt to reduce the energy' delay product. Effectively saving WNIC energy during a TCP download is difficult because TCP streams tend to be smooth, leaving little potential sleep time. The basic idea behind our technique is that 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 predictable bursts, trading lower WNIC energy cost for increased transmission time. Our technique does not rely on any assistance from the server, a proxy, or IEEE 802.11b power-saving mode. Results show that in Internet experiments our scheme outperforms baseline TCP by 64% in the best case, with an average improvement of 19%.