Microsoft KB Archive/166475

= NWLNKSPX Retransmission Problem Over a Slow Link =

Article ID: 166475

Article Last Modified on 11/1/2006

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APPLIES TO


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

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This article was previously published under Q166475



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.  Run Registry Editor (Regedt32.exe.) Go to the following key:

NOTE: The above registry key is one path; it has been wrapped for readability. Click Add Value from the Edit menu.  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. 

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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

Keywords: kbbug KB166475

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