Apple's Bonjour Sleep Proxy service is an open source component of zero configuration networking, designed to assist in reducing power consumption of networked electronic devices. A device acting as a sleep proxy server will respond to Multicast DNS queries for another, compatible device which has gone into low power mode. The low-power-mode device remains asleep while the sleep proxy server responds to any Multicast DNS queries. When the sleep proxy server sees a query which requires the low-power-mode device to wake up, the sleep proxy server sends a special wake-up-packet to the low-power-mode device. Finally, communication parameters are updated via Multicast DNS and normal communications proceed. Apple Inc. describes the service as Bonjour Sleep Proxy in their support documents. The service supports the Wake on Demand feature, first offered in Mac OS X Snow Leopard.
The sleep proxy service responds to address resolution protocol requests on behalf of the low-power-mode device:
When a sleep proxy sees an IPv4 ARP or IPv6 ND Request for one of the sleeping device's addresses, it answers on behalf of the sleeping device, without waking it up, giving its own MAC address as the current owner of that address.
In case the low-power-mode device is communicating via Wi-Fi, the wake-up-packet is sent via Wireless Multimedia Extensions. This was not possible in previous implementations of Wake on LAN. The wireless hardware must be updated enough to include WMM support. Apple provides instructions for checking compatibility with this feature for Macintosh computers.
Supported services and examples
The sleep proxy service is able to advertise any Bonjour-supported services, while the host computer sleeps. Some examples of supported services are:
File sharing: a host supporting the sleep proxy service, which offers file services, may go to sleep as needed. When someone needs to access shared files, the host will wake up automatically.
iTunes library sharing: the computer hosting the iTunes library may go to sleep, and will automatically wake when someone wishes to browse the iTunes library from a different PC.
Printer sharing: a printer may be connected and shared from a computer supporting sleep proxy service. The computer can go to sleep when not in use, but will wake when needed to service a print job being sent from a different computer.
SSH: a computer offering SSH access may go to sleep, and awaken via the sleep proxy service when an SSH login is initiated.
