NWLNKSPX Retransmission Problem Over a Slow Link

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

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

Use the Hotfix and update the following registry entry.

1. Run Registry Editor (Regedt32.exe.)

2. From the HKEY_LOCAL_MACHINE subtree, go to the following key:

         \SYSTEM\CurrentControlSet\Services\NwLnkSPX\Parameters
   

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