Support for Windows XP has ended
Microsoft ended support for Windows XP on April 8, 2014. This change has affected your software updates and security options. Article ID: 328890 - View products that this article applies to. System TipThis article applies to a different version of Windows than the one you are using. Content in this article may not be relevant to you.Visit the Windows 7 Solution Center This article was previously published under Q328890 SUMMARYTcpAckFrequency is a new registry entry in Microsoft Windows XP and Microsoft Windows Server 2003 that determines the number of TCP acknowledgments (ACKs) that will be outstanding before the delayed ACK timer is ignored. MORE INFORMATION As specified in RFC 1122, TCP uses delayed acknowledgments
to reduce the number of packets that are sent on the media. Instead of sending
an acknowledgment for each TCP segment received, TCP in Windows 2000 and later
takes a common approach to implementing delayed acknowledgments. As data is
received by TCP on a particular connection, it sends an acknowledgment back
only if one of the following conditions is true:
Important Before you edit this registry entry, you must first install the hotfix that is described in the following article: 815230
(http://support.microsoft.com/kb/815230/
)
Changing the TcpAckFrequency value to 1 does not have any effect
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 WindowsSubkey: If you set the value to 1, every packet is acknowledged
immediately because there is only one outstanding TCP ACK as a segment is just
received. The value of 0 (zero) is not valid and is treated as the default, 2.
The only time the ACK number is 0 is when a segment is not received and the
host is not going to acknowledge the data. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\<Interface GUID> Entry: TcpAckFrequency Value Type: REG_DWORD, number Valid Range: 0-255 Default: 2 Description: Specifies the number of ACKs that will be outstanding before the delayed ACK timer is ignored. Microsoft does not recommend changing the default value without careful study of the environment. For more information, visit the following Microsoft Web page: http://technet2.microsoft.com/WindowsServer/en/library/823ca085-8b46-4870-a83e-8032637a87c81033.mspx?mfr=true
(http://technet2.microsoft.com/WindowsServer/en/library/823ca085-8b46-4870-a83e-8032637a87c81033.mspx?mfr=true)
PropertiesArticle ID: 328890 - Last Review: February 28, 2007 - Revision: 4.5 APPLIES TO
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