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What's New in Power Management for Network Devices

Updated: October 23, 2009

Applies To: Windows 7

Enhancements in Windows® 7 have been made in the areas of Wake on LAN, Wake on Wireless LAN, and Low Power on Media Disconnect (sometimes referred to as "D3 on disconnect").

For more information about configuring the features listed in this topic, see Power Management for Network Devices in Windows 7.

Who will want to use power management for networking devices?

Users, IT professionals, and OEMs who are interested in understanding and configuring the power management for network devices in Windows 7 will be interested in these features.

What are the new and changed features?

Wake on LAN and Wake on Wireless LAN

Wake patterns refer to network packet filters that determine if incoming network traffic should wake the computer. Wake on LAN is enabled by default in Windows 7. The Wake on LAN patterns were designed to ensure that the computer wakes when accessed by the network while minimizing spurious wakes. Windows 7 does not wake on directed packets (such as ping), which have been known to cause frequent and unnecessary wakes.

In addition to more targeted wake patterns, Windows 7 adds support for Address Resolution Protocol (ARP) and Neighbor Solicitation (NS) offloads. ARP and NS protocols map Internet Protocol (IP) addresses to a MAC address. ARP and NS protocols are commonly used to verify whether a computer is still present on the network, often without actually needing to access the computer. By offloading ARP and NS responses to the network adapter, the computer is no longer woken up merely to maintain network presence. Support for these offloads depends on the network adapter and driver (NDIS 6.20) and may not be available on older hardware.

Low Power on Media Disconnect

Lower Power on Media Disconnect is a new Windows 7 feature that enables the network adapter to go to sleep when it is not in use. By placing the network adapter in the low power state when the LAN cable is unplugged and the computer is running, the computer saves energy. This feature is only available when supported by the network adapter.

These enhancements in Windows 7 improve the ability of the operating system to stay asleep while still maintaining a network presence. This helps enterprise and home computers to save energy by entering into sleep mode when they are not in use.

What's the impact of these changes on power management for network devices?

Because of the changes in Wake on LAN in Windows 7, you will notice that your computer will sleep for longer when compared to Windows Vista—saving more energy.

How can power management for network devices be used?

The following scenarios illustrate the new capabilities of power management for network devices:

  • Sharing media content. In the home, a Windows 7–based computer that shares media content through Media Center can go to sleep and be remotely woken when the content is accessed. A media device, such as other Windows 7 computers, an Xbox® video game system, or a Media Extender, wakes the sleeping computer by sending a Magic Packet. This scenario works with any network adapter because all modern network adapters support Wake on LAN and Magic Packet.

  • noteNote
    The following scenarios will work only if ARP and NS offloads are supported by the network adapter.

    Sharing files and printers. Users often share files and printers over the network. With Windows 7, the computer can go to sleep when idle, saving energy. When another computer on the network attempts to print or access a file, a request is sent to wake the computer. The computer wakes and accepts the connection.

  • Connecting to a remote computer. Corporate users often connect remotely to their work computer from home for tasks such as checking e-mail and retrieving files. From home, they initiate a Remote Desktop connection to their work computer on the corporate network. The work computer has idled to sleep to save energy, but when the user initiates a Remote Desktop connection, the work computer wakes from sleep. The user then has access to work resources.

  • Updating computers in an enterprise. Computers in an enterprise will wake when an IT administrator accesses the computer to administer an update. After the update is complete, the computer will go back to sleep again.

  • Saving power without using the sleep feature. Windows 7 can also save power used by the adapter when the system is awake. This is done by putting the Ethernet network adapter into a lower power state whenever the media cable is disconnected.

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