When you use a USB-to-Serial converter to connect a device to a Windows XP-based computer, the data transfer from the computer to the device is slower than expected.

For example, assume that you connect a Windows Mobile-based device to a Windows XP-based computer through an "ActiveSync over serial" port. In this situation, the data transfer from the computer to the Windows Mobile-based device is much slower than the data transfer from the Windows Mobile-based device to the computer.

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This issue occurs because the Usbser.sys driver does not follow the USB specification. When the computer transfers data to a mobile device, the transfer process is based on the Usbser.sys driver. The Usbser.sys driver does not send zero-length packets when the total transfer size is an integer multiple of the packet size. However, zero-length packets are required by the USB specification so that the device can recognize when the packet transfer is finished.

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Update information

The following file is available for download from the Microsoft Download Center:

Download the Update for Windows XP (KB943198) package now. (http://www.microsoft.com/downloads/details.aspx?FamilyId=F2F0A7C2-3B44-4D2E-9640-E0D21818763E)

Release Date: February 26, 2008

For more information about how to download Microsoft support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file.

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Prerequisites

You must have Windows XP Service Pack 2 installed on the computer.

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Restart requirement

You must restart your computer after you apply this update.

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Update replacement information

This update does not replace any other previously released updates.

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Registry information

To use this update, you do not have to make any changes to the registry.

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File information

The English version of this update has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

Windows XP SP2, x86-based versions

File name	File version	File size	Date	Time	Platform
Usbser.sys	5.1.2600.3226	26,112	01-Oct-2007	13:40	x86

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Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

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For more information, click the following article number to view the article in the Microsoft Knowledge Base:

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