DOCUMENT:Q232512  16-MAY-2002  [winnt]
TITLE   :TCP/IP may Retransmit Packets Prematurely
PRODUCT :Microsoft Windows NT
PROD/VER::4.0
OPER/SYS:
KEYWORDS:kbWinNT4sp6fix

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Windows NT Server version 4.0, Terminal Server Edition 
 - 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
==========

Windows NT Server or Workstation 4.0
------------------------------------

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/

-or-

 - 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://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS


Windows NT Server 4.0, Terminal Server Edition
----------------------------------------------

To resolve this problem, obtain the latest service pack for Windows NT Server
4.0, Terminal Server Edition. For additional information, please see the
following article in the Microsoft Knowledge Base:

   Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack


STATUS
======

Microsoft has confirmed this to be a problem in Windows NT 4.0 and Windows NT
Server 4.0, Terminal Server Edition. This problem was first corrected in Windows
NT Server version 4.0, Terminal Server Edition Service Pack 6.

MORE INFORMATION
================

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

For additional information about this issue as it pertains to Microsoft Windows
95/98, please see the following article in the Microsoft Knowledge Base:

   Q236926 Windows 95/98 TCP/IP May Retransmit Packets Prematurely

Additional query words: premature

======================================================================
Keywords          : kbWinNT4sp6fix 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbNTTermServ400 kbNTTermServSearch
Version           : :4.0
Hardware          : ALPHA x86
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2002.