Copying Files from Windows NT Using NBF Can Be Very Slow

 Last reviewed: September 1, 1996
Article ID: Q119644
The information in this article applies to:
  • Microsoft Windows NT operating system version 3.1
  • Microsoft Windows NT Advanced Server version 3.1

SYMPTOMS

When you connect to a Windows NT computer from a computer with a very slow network card (for example, the 3Com 3c501 EtherLink card) installed, copying files to the workstation from the server can be extremely slow when using NetBEUI as the protocol.

CAUSE

The 3Com 3c501 card can only cope with a send window size of one. Windows NT dynamically adapts the send window size for a session to cope with the performance of different network cards and differing network conditions, however it does not set it to a value less than two. This means that the server always sends at least two data packets before expecting an acknowledgment from the workstation. Because the network card in the workstation can only cope with one packet at a time, the second packet is lost and the workstation only acknowledges receipt of the first packet. The server then has to resend the second packet.

RESOLUTION

A new Registry parameter called MinimumSendWindowLimit has been added for the Windows NT NBF (NetBEUI) protocol to allow the configuration of the minimum send window size that NBF will use. The default value is 2. To fix the above problem, this parameter needs to be changed to 1.

Use the Registration Information Editor (REGEDT32.EXE) to add this entry, as follows:

WARNING: Using Registry Editor incorrectly can cause serious, system-wide 

   problems that may require you to reinstall Windows NT to correct them.
   Microsoft cannot guarantee that any problems resulting from the use of
   Registry Editor can be solved. Use this tool at your own risk.

  • Start REGEDT32.EXE and locate the following Registry subkey: 

          HKEY_LOCAL_MACHINE\CurrentControlSet\Services\NBF\Parameters

  • From the Edit menu, choose Add Value. Enter MinimumSendWindowLimit in the Value Name field. Select REG_DWORD for the Data Type. Enter 1 in the data field. Save your changes.

  • Quit REGEDT32.

  • Quit Windows NT and restart your computer.

    STATUS

    Microsoft has confirmed this to be a problem in Windows NT and Windows NT Advanced Server version 3.1. This problem has been corrected in the latest U.S. Service Pack for Windows NT and Windows NT Advanced Server version 3.1. 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
    The 3Com product discussed here is manufactured by 3Com Corp., a vendor independent of Microsoft; we make no warranty, implied or otherwise, regarding this product's performance or reliability.

    • KBCategory: kbnetwork kbbug3.10 kbfix3.10.sp3
    KBSubcategory: ntnetserv NTSrvWkst
    Additional reference words: prodnt 3.10

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    Last reviewed: September 1, 1996
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