TN3270 Connection Requests Fail Over Slow Links (276330)


The information in this article applies to:

  • Microsoft SNA Server 4.0
  • Microsoft SNA Server 4.0 SP1
  • Microsoft SNA Server 4.0 SP2
  • Microsoft SNA Server 4.0 SP3
This article was previously published under Q276330
IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SYMPTOMS

When there are long time delays between Transfer Control Protocol (TCP) acknowledgements, as can occur in a satellite link, a backlog of outstanding requests may build up. This may cause additional TN3270 session requests to fail when you attempt to connect to the TN3270 Server. The TN3270 Server does not log any events when this problem occurs.

CAUSE

The value of the inbound connections backlog is limited to 5. If five requests are already backlogged, then new connection requests are silently rejected.

RESOLUTION

To resolve this problem, obtain the latest service pack for SNA Server 4.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack


STATUS

Microsoft has confirmed that this is a problem in Microsoft SNA Server version 4.0.

This problem was first corrected in SNA Server 4.0 Service Pack 4.

MORE INFORMATION

The TCP listen backlog value that is used by the TN3270 Server can now be overridden by a new registry entry, TCPListenBacklog. A higher backlog value will enable the server to accept more new incoming client connections that come over a slow link.

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

  1. Start Registry Editor (Regedt32.exe).
  2. Locate the following key in the registry:

    HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\TN3270\Parameters

    NOTE: The above registry key is one path; it has been wrapped for readability.
  3. On the Edit menu, click Add Value, and then add the following registry value:

    Value Name: TCPListenBacklog
    Data Type: REG_DWORD
    Value: Number of requests to be backlogged

  4. Quit Registry Editor.
Modification Type:MinorLast Reviewed:12/29/2003
Keywords:kbbug kbfix kbQFE kbSNA400PreSP4fix kbSNA400sp4fix KB276330
©2003 Microsoft Corporation. All rights reserved.