DOCUMENT:Q166475  09-AUG-2001  [winnt]
TITLE   :NWLNKSPX Retransmission Problem Over a Slow Link
PRODUCT :Microsoft Windows NT
PROD/VER:winnt:4.0
OPER/SYS:
KEYWORDS:

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The information in this article applies to:

 - Microsoft Windows NT Workstation version 4.0 
 - Microsoft Windows NT Server version 4.0 
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IMPORTANT: This article contains information about editing the registry.
Before you edit the registry, make sure you understand how to restore it if
a problem occurs. For information on how to do this, view the "Restoring
the Registry" online Help topic in Regedit.exe or the "Restoring a Registry
Key" online Help topic in Regedt32.exe.

SYMPTOMS
========

You may experience a slow response or your application may be disconnected when
your client/server application is running over a slow link. This most noticeably
occurs when your client/server application uses SPX as its transport mechanism.

CAUSE
=====

Windows NT's NWLNKSPX protocol calculates retransmission time based on the Round
Trip Time (RTT) calculation and is calculated for each packet. As a result, the
retransmission time is dynamic and adjusts itself according to the network load
and congestion. Currently there is no option in NWLNKSPX to disable RTT and the
specified static retransmission time.

RESOLUTION
==========

Apply the latest service pack, and then update the following registry entry:

WARNING: Using Registry Editor incorrectly can cause serious problems that may
require you to reinstall your operating system. Microsoft cannot guarantee that
problems resulting from the incorrect use of Registry Editor can be solved. Use
Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And
Values" online Help topic in Registry Editor (Regedit.exe) or the "Add and
Delete Information in the Registry" and "Edit Registry Data" online Help topics
in Regedt32.exe. Note that you should back up the registry before you edit it.

1. Run Registry Editor (Regedt32.exe.)

2. Go to the following key:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
   \NwLnkSPX\Parameters

   NOTE: The above registry key is one path; it has been wrapped for readability.

3. Click Add Value from the Edit menu.

4. Add the following:

      Value Name: DisableRTT
      Data Type: REG_DWORD
      Data: 1 (Default 0)

   A data value of 1 disables the Round Trip Time calculation algorithm and the
   retransmission time is set to the static value determined by the
   InitialReTransmissionTime, which is 500msec by default. You can adjust the
   InitialRetransmissionTime to control the retransmission timer.

STATUS
======

Microsoft has confirmed this to be a problem in Windows NT version 4.0. This
problem was corrected in the latest Microsoft Windows NT 4.0 U.S. Service Pack.
For information on obtaining the service pack, query on the following word in
the Microsoft Knowledge Base (without the spaces):

   S E R V P A C K


Additional query words:

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Keywords          :  
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400
Version           : winnt:4.0
Issue type        : kbbug

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Copyright Microsoft Corporation 2001.