TN3270 Emulators May Fail to Reconnect After Inactivity Timeout

ID: Q230220

The information in this article applies to:

Microsoft SNA Server, version 4.0SP2

SYMPTOMS

When TN3270 emulators are connecting through the TN3270 server included with SNA Server 4.0 Service Pack 2 (SP2) to a host session, the TN3270 emulators may fail to automatically reconnect when the session ends because of inactivity.

The following message may be displayed in the TN3270 emulator window when the TN3270 server ends the session due to inactivity:

TN3270E Service Error 503

Session terminated due to inactivity.

NOTE: This message may not be displayed in the same manner in all TN3270 emulators.

In addition, the following event will be logged in the Windows NT application event log by the TN3270 server when a TN3270 session is ended due to inactivity:

Event ID: 603
Source: TN3270 Server
Description: TN3270(E) session with client at <TCP/IP Address> (port <IP Port>) using LU <TN3270 LU Name> terminated abnormally because:

TN3270E Service Error 503

Session terminated due to inactivity.

When TN3270 emulators are configured to autoconnect, they successfully reconnect to a host session after receiving the previous inactivity timeout message without any user intervention when they are connecting to a host session through a TN3270 server included with SNA Server versions 4.0 Service Pack 1 and earlier.

CAUSE

The TN3270 emulator is unable to reconnect to the TN3270 server because the previous TN3270 session is not being cleaned up properly. This occurs because the TN3270 server has issued an RUI_READ() to the TN3270 client that never completes because the TN3270 emulator does not send any data to the TN3270 server after it receives the inactivity error message described above. Because the TN3270 server is waiting for the RUI_READ() to complete, it does not reset the underlying TCP/IP session that is open between the TN3270 server and the TN3270 client. The TN3270 emulator does not attempt to reconnect while the previous TCP/IP session is still open.

The TN3270 server in SNA Server 4.0 SP2 was updated to use Windows NT I/O Completion Ports to provide performance improvements. It is the use of I/O Completion Ports that causes this particular problem to occur. Therefore, the TN3270 server included with earlier versions of SNA Server does not exhibit this behavior.

RESOLUTION

To resolve this problem, obtain the latest service pack for SNA Server version 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

WORKAROUND

The TN3270 emulator will reconnect to a host session if one of the following is done:

The user presses the ENTER key at the TN3270 session window.
The user explicitly disconnects/reconnects the session from within the TN3270 emulator window.

STATUS

Microsoft has confirmed this to be a problem in Microsoft SNA Server version 4.0 SP2. This problem was first corrected in SNA Server version 4.0 Service Pack 3.

MORE INFORMATION

For additional information about a similar TN3270 issue with SNA Server 4.0 SP2, please click the article number(s) below to view the article(s) in the Microsoft Knowledge Base:

Q239707 TN3270 Clients May Fail to Reconnect to a Host Session

Additional query words:

Keywords : sna4sp3fix
Version : WINDOWS:4.0SP2
Platform : WINDOWS
Issue type : kbbug