Knowledge Base

You may experience connectivity issues or performance issues when you connect a mobile PC that is running Windows Vista to a wireless access point

Article ID: 928152

Article Last Modified on 3/17/2007

APPLIES TO

Windows Vista Ultimate
Windows Vista Enterprise
Windows Vista Business
Windows Vista Home Premium
Windows Vista Home Basic
Windows Vista Starter
Windows Vista Enterprise 64-bit edition
Windows Vista Home Basic 64-bit edition
Windows Vista Home Premium 64-bit edition
Windows Vista Ultimate 64-bit edition

SYMPTOMS

You may experience random connectivity issues when you connect a Windows Vista-based mobile PC to certain Wi-Fi "hot spots." These connectivity issues include the following:

The wireless network connection is dropped.
You experience poor performance.

You experience these issues if the Windows Vista-based computer is running on battery power.

Note You may also experience these issues when you connect a Windows Vista-based mobile PC to a wireless access point (AP) in a small office/home office (SOHO) environment or in an enterprise environment.

CAUSE

This issue occurs if the Wi-Fi hot spot uses wireless APs or routers that do not support the 802.11 power save protocol.

This issue occurs because of the power saving features that are included in Windows Vista. The default power plan that Windows Vista uses for a mobile PC is the Balanced power plan. In pre-release versions of Windows Vista, the following is true for mobile PCs that are configured to use the Balanced power plan:

When the mobile PC is plugged into a power source, the wireless network adapter is configured to use Maximum Performance mode. This turns off 802.11 power save mode.
When the mobile PC is running on battery power, the wireless network adapter is configured to use Medium Power Save mode. This uses the 802.11 power save mode.

When an 802.11 wireless network adapter that is set to use power save mode wants to enter a sleep state, the adapter indicates this intention to the wireless AP. The adapter does this by setting the power save option in its packets or in the 802.11 frames that it sends to the wireless AP. In this scenario, the following behavior should occur:

When the wireless AP receives the frames that have the power save option set, the wireless AP determines that the client network adapter that sent the frames wants to enter a power saving state.
The wireless AP then buffers packets that are destined for the client network adapter.
When the radio of the client network adapter turns on, the client network adapter then communicates with the AP to retrieve the buffered packets.

This behavior enables the wireless network adapter to use less power and to wake up periodically at the correct time to receive network traffic from the AP.

If the wireless AP does not support this feature correctly, the wireless AP continues to send packets to the client network adapter even if the client network adapter radio is turned off. Therefore, these packets are lost. In this scenario, the symptoms that you experience may vary depending on the phase of the wireless connection in which these packets are lost.

WORKAROUND

To work around this issue, use one of the following methods, as appropriate for your situation.

Method 1: Connect the mobile PC to a power source

When you plug the mobile PC into a power source, Windows Vista switches the wireless network adapter power setting in the default power plan from the Medium Power Save setting to the Maximum Performance setting. This turns off the 802.11 power save mode.

Method 2: Modify the default power saving power plan

Modify the default on-battery power setting for the wireless network adapter. Configure the wireless network adapter to use the Maximum Performance setting when Windows Vista is configured to use the Balanced power plan or the Power saver power plan. To do this, follow these steps:

Click Start, type Power Options in the Start Search box, and then click Power Options in the Programs list.

If you are prompted for an administrator password or confirmation, type your password or click Continue.

Click Change plan settings under the power plan that is selected. For example, if the Balanced option is selected, click Change plan settings under Balanced.
Click Change advanced power settings.
In the Power Options dialog box, expand Wireless Adapter Settings, and then expand Power Saving Mode.
In the list that appears next to On battery, click Maximum Performance, and then click OK.

Method 3: Use the "High performance" power plan

If the computer is running on a power plan other than the High performance power plan when you connect to a wireless network, manually change the power plan to High performance. To do this, follow these steps:

Click Start, type Power Options in the Start Search box, and then click Power Options in the Programs list.

If you are prompted for an administrator password or confirmation, type your password or click Continue.

Note You can also right-click the battery icon in the notification area to access the Power Options command.

Click High performance.

MORE INFORMATION

To help work around this issue, the default On battery power saving setting that is in the Wireless Adapter Settings option is modified in the release version of Windows Vista. In the release version of Windows Vista, the default On battery power saving setting is set to Maximum Performance. This change affects the Balanced power saving mode. Additionally, this change affects the running time of the computer when it runs on battery power. This change reduces the battery time by between approximately two percent and nine percent running time.

Note This change may not be reflected in original equipment manufacturer (OEM) versions of Windows Vista that may be installed on mobile PCs. Computer manufacturers may change the default Windows Vista power settings according to their guidelines.

Although you are more likely to experience this issue in Windows Vista, you may also experience this issue when you connect to a Wi-Fi hot spot by using a Microsoft Windows XP-based computer. This issue is less likely to occur in Windows XP because the default power saving mode in Windows XP does not turn on the 802.11 power save mode of the wireless network adapter. However, if you do experience this issue in Windows XP, you can modify the power saving settings of the wireless network adapter to work around this issue. To do this, follow these steps:

Click Start, click Run, type ncpa.cpl, and then click OK.
In the Network Connections dialog box, right-click the wireless network adapter, and then click Properties.
Click the Advanced tab, and then modify the power management settings. For example, click Power Management in the Property list, drag the Value slider to the power management setting that you want to use, and then click OK.

Note These settings may differ depending on the manufacturer of the wireless network adapter.

Keywords: kbtshoot kbinfo kbwireless kbnetworkconnectivity kbenv kbbroadband kbprb kbexpertisebeginner kbhardware KB928152

Microsoft KB Archive/928152

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