Skilled in the Art of Being Idle: Reducing Energy Waste in Networked Systems

This paper evaluates the viability of putting computers to sleep while preventing disruption from the machine not being on the network. Current platforms have ‘wake-on-LAN’ functionality, enabling machines to be woken up from a low-power state by a ‘magic packet’. A simple proxy could examine traffic destined to the machine and inject the magic packet before traffic to which the machine needs to respond. A more sophisticated version of this proxy could respond on the machine's behalf for simple but important queries. Using network traces for desktop machines in both home and work environments, this paper evaluates the likely power savings achieved with various levels of proxy sophistication.

The traces reveal that there is a lot of background noise on networks. Some of this traffic is broadcast at the Ethernet level but not actually logically directed to the end host (for example IPX traffic, routing backup traffic, ARP requests not for the end host's IP). Some is for protocols that require periodic maintainence traffic to maintain liveness, e.g. ARP (when querying the host), IGMP (if the host belongs to IP multicast groups), DHCP, TCP (for keepalives), SSDP. Such traffic was frequent enough in the author's traces that a proxy that would not handle that traffic would not be able to allow end hosts to sleep a substantial amount of time without disrupting service. Making such simple fill-in-the-blank replies for a handful of services and conservatively waking machines up for other services is all that would be required to allow machines to stay asleep for most their idle periods without sacrificing availability. Problematically, all it takes to disrupt this result is one misconfigured service (for example, the machine updating service the authors observed in the enterprise environment).