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Q276330: TN3270 Connection Requests Fail Over Slow Links

Article: Q276330
Product(s): Microsoft SNA Server
Version(s): 4.0,4.0 SP1,4.0 SP2,4.0 SP3
Operating System(s): 
Keyword(s): kbsna300sp1 kbsna300sp2 kbsna300sp3 kbsna300sp4 sna4 kbsna400sp1 kbsna400sp2 kbsna400sp
Last Modified: 11-JUN-2002

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The information in this article applies to:

- Microsoft SNA Server, versions 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3 
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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:

  Q256986 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, please see the following article in the Microsoft
Knowledge Base:

  Q215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack



STATUS
======

Microsoft has confirmed this to be 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.

Additional query words:

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Keywords          : kbsna300sp1 kbsna300sp2 kbsna300sp3 kbsna300sp4 sna4 kbsna400sp1 kbsna400sp2 kbsna400sp3 kbSNA400sp4fix kbSNA400PreSP4fix 
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ400 kbSNAServ400SP1 kbSNAServ400SP2 kbSNAServ400SP3
Version           : :4.0,4.0 SP1,4.0 SP2,4.0 SP3
Issue type        : kbbug
Solution Type     : kbfix

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