Wireless Network Interface Energy Conservation
Placeshifting systems stream videos from the home to a single remote user using the limited upstream capacity of the home broadband link. We analyze the behavior of two placeshifting systems each using two types of broadband networks. We show that the duration between packets did not depend on the way that the servers were sending the packets through the bottleneck link. Even though both of these systems used TCP, the duration between packets did not follow the round trip times either. Instead, it depended on the particular broadband network. Our analysis shows how the bottlenecked first mile network leads to predictable packet delivery at the remote client. Paradoxically, it also leads to shorter periods and a single packet within each data burst. We discuss the limitations imposed by this behavior on a client side energy saving mechanism. We also describe techniques that allow the placeshifting servers to better operate with client side WNIC energy saving mechanisms. Categories and Subject Descriptors
The wireless network interface (WNIC) consumes a significant portion of the laptop energy reserves . They support various power states with varying network functionality. Prior efforts [4, 9, 11, 3, 16, 14] exploited the low power states to conserve energy. Energy conservation schemes are effective for isochronous streaming media because of their predictable network behavior [3]. However, prior systems did not consider the effects of network bottleneck on packet predictability. Without any bottleneck, the packet dynamics at the client are predominantly driven by the way packets Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific were sent from the media server. For wireless users, the bottleneck link can either be in the first mile or in the last mile network. With a bottlenecked last mile network, there are no idle durations that can be exploited for energy conservation. Hence, we explore streaming scenarios using a bottlenecked first mile network. We investigate placeshifting systems that allow users to watch the video from a place that is different from the originally intended location. For example, when traveling, these systems allow a single user to remotely watch premium TV programs that they had already subscribed at their home (and thus avoid paying twice). Systems such as the EchoStar Slingbox/TV Everywhere, Sony LocationFree and TV2Me offer hardware devices that attach to the TV output. The upcoming EchoStar ViP 922 DVR will also natively offer this Slingbox functionality. Client software is available for laptops, smart phones and handheld gaming consoles. Sony and EchoStar also make dedicated wireless tablets that are designed to watch the LocationFree and Slingbox streams, respectively. The placeshifting server uses the under-provisioned upstream capacity of the broadband link; the Speed Matter’s “Survey of Internet speeds” estimates that the average upload speed in the US is 1.1 Mbps. The Slingbox consumes over eight Mbps to locally stream standard definition (SD) streams. Note that placeshifting access is one-to-one and is different frompeer-to-peer (P2P) scenarios where the same object was available elsewhere; P2P users can circumvent the low upload capacity by either accessing the object from a server or swarm from a number of different locations