Microsoft KB Archive/311084

= WinSock Traffic Is Slow Over High Speed, High Latency Links =

Article ID: 311084

Article Last Modified on 10/27/2006

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APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Professional Edition
 * Microsoft Windows NT Server 4.0 Standard Edition
 * Microsoft Windows NT Workstation 4.0 Developer Edition

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This article was previously published under Q311084



SYMPTOMS
When you transfer data by using WinSock (for example, by using FTP) over a high speed, high latency link (such as a satellite link), performance is slower than expected.



CAUSE
This behavior can occur because of the way that the Ancillary Function driver for WinSock (used by FTP and others) manages its buffers.

The Ancillary Function driver for WinSock tries to intelligently decide on a I/O Transmit Length based on how much memory is in the computer. When there is 64 megabytes (MB) or less, it arbitrarily sets the I/O Length to either 4 kilobytes (KB) or 8 KB, depending on how much memory there is. When the computer has more than 64 MB, the I/O Length is increased to 64 KB and the problem disappears.

NOTE: This only applies to the server product. A workstation always uses the 4 KB I/O Length.



RESOLUTION
To work around this behavior, increase the available physical memory in the server to more than 64 MB.



STATUS
This behavior is by design.



MORE INFORMATION
For additional information about related topics, click the article number below to view the article in the Microsoft Knowledge Base:

129593 Windows NT Workstation and Server Optimized For Different Roles

Additional query words: afd.sys

Keywords: kbenv kbnetwork kbprb KB311084

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