Microsoft KB Archive/276330

= TN3270 Connection Requests Fail Over Slow Links =

Article ID: 276330

Article Last Modified on 12/29/2003

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APPLIES TO


 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 4.0 Service Pack 1
 * Microsoft SNA Server 4.0 Service Pack 2
 * Microsoft SNA Server 4.0 Service Pack 3

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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.

 Start Registry Editor (Regedt32.exe). 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. 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

 Quit Registry Editor.</ol>

Keywords: kbbug kbfix kbsna400presp4fix kbqfe kbsna400sp4fix KB276330

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