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IP packets that are transferred over aggregated links may be dropped by the Multilink feature on a Windows XP-based computer

Article ID: 946775 - View products that this article applies to.

Hotfix Download Available

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SYMPTOMS

Consider the following scenario:

You are running a Windows XP-based computer.
You use the Multilink feature for multiple-device dialing to aggregate the links of multiple broadband wireless modems.

In this scenario, IP packets that are transferred over the aggregated links may be dropped.

For example, assume that you use three wireless modems to connect to your Internet service provider (ISP). Each of these modems supports a data transfer rate of 3 megabits per second (Mbps). When you aggregate the links of these three modems, you expect a maximum transfer rate of 9 Mbps in total. However, when the actual transfer rate reaches 6 Mbps, the IP packets over the aggregated links may be dropped intermittently.

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CAUSE

The Ndiswan.sys driver maintains a buffer that is responsible for holding the received packets for reassembly. There are 64 of these buffers. This number is sufficient for dial-up modems. When the combined bandwidth exceeds 6 Mbps, fragments are likely to be dropped before they are reassembled.

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RESOLUTION

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

(http://support.microsoft.com/contactus/?ws=support)

Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, you must have Windows XP Service Pack 2 (SP2) or a later service pack installed. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

322389

(http://support.microsoft.com/kb/322389/ )

How to obtain the latest Windows XP service pack

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

Registry information

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756

(http://support.microsoft.com/kb/322756/ )

How to back up and restore the registry in Windows

After you apply this hotfix, you can use a registry entry to configure the size of the reassembly buffer in the Ndiswan.sys driver. To do this, follow these steps:

Click Start, click Run, type regedit, and then press ENTER.
Locate the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters
Right-click Parameters, point to New, and then click DWORD Value.
Type RecvBufferCount, and then press ENTER.
Right-click RecvBufferCount, and then click Modify.
Under Base, click Decimal, enter the value that you want in the Value data box, and then click OK. This value defines the number of reassembly buffers that are available. You can set this value to any number from 64 to 6400.
Exit Registry Editor.

File information

The English version of this hotfix 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 with Service Pack 2, x86-based versions

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File name	File version	File size	Date	Time	Platform
Ndiswan.sys	5.1.2600.3355	91,776	21-Apr-2008	09:58	x86

Windows XP with Service Pack 3, x86-based versions

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File name	File version	File size	Date	Time	Platform
Ndiswan.sys	5.1.2600.5584	91,520	21-Apr-2008	12:56	x86

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STATUS

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

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MORE INFORMATION

For more information about how to set up multiple-device dialing in Windows XP, click the following article number to view the article in the Microsoft Knowledge Base:

307849

(http://support.microsoft.com/kb/307849/ )

How to set up multiple-device (Multilink) dialing in Windows XP

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

824684

(http://support.microsoft.com/kb/824684/LN/ )

Description of the standard terminology that is used to describe Microsoft software updates

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