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How Windows Vista RTM Build Addresses Wireless Connectivity Issues

jleznek on Vista blog —”Wireless access is a key feature in Windows Vista, and it needs to work as reliably as possible for users.  In the final version of Windows Vista, the default power setting for 802.11 wireless adapters was changed to “Maximum Performance” to offer seamless wireless access experience and solve connectivity issues with certain access points. Users and OEMs can change the setting value to deliver additional power savings, if they want to further extend the battery life.

Context: Test results from Microsoft and our customers show that some Windows Vista beta users experienced connectivity problems when connecting to public WiFi hotspots.  In many cases, the root cause of the problem is access point or router hardware which is not compatible with the 802.11 power save protocol.  The symptoms of the problem are either failing connections or extremely poor connection performance and throughput.  Typically, these problems are experienced only when the computer is on battery power—connecting to AC power solves the issue.

By default, Windows Vista enables many platform power management features, including wireless adapter power saving modes.  On all Windows Vista systems, the default power plan is Balanced, and pre-release versions of Windows Vista enabled Medium Power Savings for the 802.11 wireless adapter when the computer is on battery power.  When the computer is on AC power, Maximum Performance (no power savings) is enabled for the 802.11 wireless adapter.   This explains why connecting to AC power solves the connectivity issue for many users, as did changing the power plan to High Performance or changing the wireless adapter power setting to Maximum Performance in Power Options.

When power save mode is enabled for an 802.11 wireless network adapter, the adapter periodically enters a low-power state where the radio transmitter and receiver are in “sleep” mode.  The wireless adapter in the computer (client adapter) indicates the “sleep” mode by setting the power save option in its packets or 802.11 frames sent to the access point. The access point receiving frames with the power save option set determines that the client adapter wishes to enter power save mode, and begins buffering packets for the client adapter while it is asleep. The client adapter’s radio periodically wakes up and communicates with the access point to retrieve the buffered packets. This scheme enables the wireless adapter to consume less power by sleeping and waking periodically, just at the right time to receive network traffic from the access point.

However, this power savings scheme for 802.11 wireless adapters depends on cooperation of the access point.  The problem is that many access points do not implement or support the power save feature correctly.  Some broken access points keep sending the packets to the client—even when the client adapter’s radio is asleep.  The packets sent to the client radio while it is asleep are lost, which leads to the connectivity, performance and throughput issues that some Windows Vista beta users were encountering. 

Wireless access is a key feature in Windows Vista, and it needs to work as reliably as possible for users.  In the final version of Windows Vista, the default power setting for the 802.11 wireless adapter is “Maximum Performance”.  This means, that by default, on battery power or on AC power, wireless adapters will not use power-saving modes.   OEMs are able to change any power setting when they are building systems with Windows Vista, so the setting might be different on a machine released with Windows Vista.  The obvious downside to the power setting change is a potential decrease in computer battery life.  But, it may be difficult to diagnose the root cause of the wireless connectivity problem, so the wireless power setting was changed accordingly for the most common default case.

If you want to re-enable power savings for your 802.11 wireless adapter, you can easily do this in Windows Vista.  There are two primary ways:

  • Change the wireless power saving setting:
    • Open Power Options in Control Panel
    • Choose Change Settings for the current power plan
    • Choose Change Advanced Power Settings
    • Expand Wireless Adapter Settings
    • Expand Power Saving Mode
    • Choose Maximum Power Saving, Medium Power Saving, Low Power Saving to enable various levels of 802.11 power save modes.
  • Choose the Power Saver power plan:
    • Click on the battery meter on the desktop and choose Power Saver.
    • The Power Saver plan has 802.11 power saving mode enabled for both battery and AC power.

Microsoft is committed to both seamless wireless access and extended battery life.  We are actively working with industry partners to fix wireless access points so they work correctly with 802.11 power save mode. 

Vista Blog

RTM, Addresses, Wireless Connectivity, Issues

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