TCP/IP May Retransmit Packets Prematurely

ID: Q232512

The information in this article applies to:

Microsoft Windows NT Workstation version 4.0
Microsoft Windows NT Server version 4.0

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 that 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

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the individual software update. For information on obtaining the latest service pack, please go to:

http://www.microsoft.com/windows/servicepacks/

Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

For information on obtaining the individual software update, contact Microsoft Product Support Services. 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

STATUS

Microsoft has confirmed this to be a problem in Windows NT 4.0. This problem was first corrected in Windows NT 4.0 Service Pack 6.

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 NT4SP6Fix
Version : winnt:4.0
Platform : winnt
Issue type : kbbug