TCP/IP May Retransmit Packets Prematurely

ID: Q232512

The information in this article applies to:

SYMPTOMS

When transmitting data over high-delay networks (for example, satellite links), transfer throughput may be lower than expected and the number of packets retransmitted may be unnecessarily high.


CAUSE

This problem occurs because TCP uses a retransmit timer to retransmit packets which do not appear to have reached the receiver. To set this timer, TCP uses information about the historical Round Trip Time (RTT) for each connection, which it measures by observing the time between sending packets and receiving acknowledgments for them.

The Microsoft Windows NT 4.0 TCP/IP stack incorrectly computes the retransmit timer because of a math error. When transmitting packets over high-delay networks, this can result in unnecessary retransmissions and lower throughput.


RESOLUTION

A supported fix that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific problem, Microsoft recommends that you wait for the next Windows NT 4.0 service pack that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://www.microsoft.com/support/supportnet/overview/overview.asp
The English version of this fix should have the following file attributes or later:

   Date      Time                 Size    File name     Platform
   -------------------------------------------------------------
   06/04/99  12:12p               150,768 Tcpip.sys     (x86)
   06/04/99  12:11p               273,968 Tcpip.sys     (Alpha)

NOTE: If this product was already installed on your computer when you purchased it from the Original Equipment Manufacturer (OEM) and you need this fix, please call the Pay Per Incident number listed on the above Web site. If you contact Microsoft to obtain this fix, and if it is determined that you only require the fix you requested, no fee will be charged. However, if you request additional technical support, and if your no-charge technical support period has expired, or if you are not eligible for standard no-charge technical support, you may be charged a non-refundable fee.

For more information about eligibility for no-charge technical support, see the following article in the Microsoft Knowledge Base:
Q154871 Determining If You Are Eligible for No-Charge Technical Support


STATUS

Microsoft has confirmed this to be a problem in Windows NT 4.0.


MORE INFORMATION

The TCP retransmission count can be observed using the Performance Monitor utility or using the "netstat -s" command.

Additional query words: premature 


Keywords          : kbbug4.00 kbfix4.00 
Version           : winnt:4.0
Platform          : winnt 
Issue type        : kbbug

Last Reviewed: July 28, 1999