SNA Server Handling of 3270 LU Session Cleanup

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When using pooled 3270 LUs with SNA Server, a 3270 user may access the previous user's host application session. This occurs when the host did not clean up the 3270 application after receiving a TERM-SELF message from SNA Server on the session. If this occurs, the NOTERMSELF:REG_SZ:YES registry setting should be used to force SNA Server to send an UNBIND(Cleanup) when the user ends their 3270 session, or when the user's client-server LAN session is lost.

The NOTERMSELF registry setting is described below, and in the SNA Server 2.1 or 3.0 "Reference Guide".

When a 3270 user closes their emulation session, or if the SNA Server client loses its LAN connection to the SNA Server, SNA Server sends a TERM-SELF on the SSCP-LU session to request that the host unbind the PLU-SLU session. On some host systems, this TERM-SELF message does not cause the 3270 application session to be cleaned up.

To force SNA Server to send an UNBIND(Cleanup) to the host:

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. Run Registry Editor (REGEDT32.EXE).
2. From the HKEY_LOCAL_MACHINE subtree, go to the following key:

   \SYSTEM\CurrentControlSet\Services\SnaServr\Parameters
   						

3. On the Edit menu, click Add Value.
4. Add the following:
   Value Name: NOTERMSELF
   Data Type: REG_SZ
   String: YES
5. Click OK.

When this variable is set to YES, 3270 sessions are terminated directly by sending UNBIND(cleanup). Otherwise, a TERM-SELF is sent to solicit UNBIND from the host. Setting this variable to YES is a workaround for host-based session monitors that mark the LU as inactive after the TERM-SELF sequence, or do not properly unbind the application session.

If CICS is being used and the CICS "dedicated LU" feature is enabled at the host, or if certain host session monitors are being used (such as "TPX"), the host 3270 application session may not be cleaned up even if SNA Server is configured to send Unbind(cleanup).

When using dedicated LUs, CICS preserves the user's host application session even when the user were to turn off their 3270 terminal. So, this host feature assumes that a given LU will always be accessed by a specific user. If you want to use the dedicated LU feature, consider assigning specific 3270 LUs to specific users using SNA Server Admin, and do not use pooled 3270 LUs. Otherwise, if a user disconnects from their emulation session, the next user who acquires the same 3270 LU (through the use of a 3270 pool) reconnects to the same host application state of the previous user.