'Sleep Talking' PCs Save Energy, Money

Personal computers may soon save large amounts of energy by "sleep talking." Computer scientists at the University of California San Diego and Microsoft Research have created a plug-and-play hardware prototype for personal computers that induces a new energy saving state known as "sleep talking."

Normally PCs can be in either awake mode—where they consume power even if they are not being used, or in a low power sleep mode—where they save substantial power but are essentially inactive and unresponsive to network traffic. The new sleep talking state provides much of the energy savings of sleep mode and some of the network-and-Internet-connected convenience of awake mode.

UC San Diego computer science Ph.D. student Yuvraj Agarwal presented this work on April 23, 2009 at the USENIX Symposium on Networked Systems Design and Implementation (NSDI 2009). Computer scientists at UC San Diego and Microsoft Research in Redmond, Washington and Cambridge, UK collaborated on this project and the NSDI 2009 paper, "Somniloquy: Augmenting Network Interfaces to Reduce PC Energy Usage."

"Large numbers of people keep their PCs in awake mode even though the PCs are relatively idle for long blocks of time because they want to stay connected to an internal network or the Internet or both," says Agarwal. "I realized that most of the tasks that people keep their computers on for—like ensuring remote access and availability for virus scans and backup, maintaining presence on instant messaging (IM) networks, being available for incoming voice-over-IP (VoIP) calls, and file sharing and downloading—can be achieved at much lower power-use levels than regular awake mode."

Following this realization, the team built a small USB-connected hardware and software plug-in system that allows a PC to remain in sleep mode while continuing to maintain network presence and run well-defined application functions. It supports instant messaging applications, VoIP, large background web downloads, peer-to-peer file sharing networks such as BitTorrent, and remote access. The computer scientists say their system is easily extensible to support other applications.

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Study: Differentiated Networks More Efficient

A new study by researchers at Rensselaer Polytechnic Institute, AT&T Labs, and the University of Nevada, Reno suggests that an Internet where all traffic is treated identically would require significantly more capacity than one in which differentiated services are offered.

Findings from the study were presented June 22 at the 15th IEEE International Workshop on Quality of Service (IWQoS 2007) in Evanston, Ill. IWQoS is a premier workshop on quality of service research, featuring rigorously reviewed technical sessions and papers.

As the Internet becomes more crowded with high-bandwidth applications and content, a wide-ranging debate is taking place about the issue of “network neutrality,” which involves both economic and technical aspects. One aspect of the debate involves whether application traffic that requires performance assurances (e.g., VoIP) could be serviced differently, or what the impact would be if all traffic were to be treated in an undifferentiated manner.

“We wanted to take one piece of the overall debate and approach it quantitatively,” says principal investigator Shivkumar Kalyanaraman, professor of electrical, computer, and systems engineering at Rensselaer. “The study makes clear that there are substantial additional costs for the extra capacity required to operate networks in which all traffic is treated alike, and carrying traffic that needs to still be assured performance as specified in service level agreements (SLAs).”

Using computer models, the researchers compared the current “best-effort” approach with a tiered model that separates information into two simple classes — one for most types of information and another for applications requiring service level assurance for high-bandwidth content like video games, telemedicine, and Voice over Internet Protocol (VoIP).

The study was meant to answer one basic question, according to Kalyanaraman: “If I want to meet the needs of applications that require service level assurances, how much more capacity do I need"”

The additional capacity needed for an undifferentiated network compared to a differentiated network is referred to as the Required Extra Capacity. The study estimates that the Required Extra Capacity in even modestly loaded networks could approach 60 percent. At times of heavy demand on the network, the Required Extra Capacity in an undifferentiated network could amount to an additional 100 percent or more of the total capacity required when differentiation is permitted.

“Clearly, an undifferentiated network in this context is less efficient and more expensive,” says coauthor K.K. Ramakrishnan of AT&T Labs. “We believe understanding the real impacts of the alternative strategies is important as the debate about network architecture unfolds.”

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