Somniloquy: Maintaining Network Connectivity While Your Computer Sleeps

Reducing the energy consumption of computers is becoming increasingly important with rising energy costs and environmental concerns. It is especially important for mobile devices such as laptops where battery lifetime is always an issue. Sleep states such as S3 (suspend to RAM) save energy but prevent the device from responding to incoming network events, for example remote desktop logins and file transfer requests. Thus many people do not use S3 and instead leave their computers plugged in and active. Mobile users do not have this flexibility, and as a result their machines are unreachable during the periods when they are in S3. Somniloquy allows computers in S3 to be woken based on incoming network traffic such as incoming VoIP calls or remote file access requests, or other events such as the presence of particular access points. This is done by adding a secondary embedded processor attached to a network interface, forming a low-power domain that remains active even when the rest of the computer is in S3. This secondary processor acts transparently on behalf of the computer, sharing the same MAC address, IP address, host name, etc. Remote servers and network hardware remain completely unaware of the low-power state. We present a prototype implementation of Somniloquy using a USB peripheral, which is therefore easily retrofitted to existing computers. Our prototype achieves a ten-fold increase in battery lifetime compared to an idle computer not in S3, while only adding 4-7s of latency to respond to applicationlayer events. Our system allows computers to appear alwayson when they are in fact talking in their sleep.