Downstream PU Fails to Activate After Short ACTLU Response (163208)

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256986 Description of the Microsoft Windows Registry

SYMPTOMS

When a downstream PU2.0 emulator attempts to activate a session through an SNA Server, SNA Server may never send a NOTIFY (available) request to the host, causing the LU session to fail to activate.

This problem was observed when attempting to configure an ASCII-3270 protocol converter (SyncResearch SDLC/LLC2 converter) to use an SNA Server downstream PU connection.

CAUSE

SNA Server automatically sends NOTIFY (unavailable) when the upstream host connection becomes active, and it depends on the downstream PU2.0 client to send a NOTIFY (available) or a "long" ACTLU response later on. However, some downstream clients do not send a NOTIFY message and send "short" ACTLU responses, and so SNA Server never sends a NOTIFY(available) to the host.

RESOLUTION

An update to Snaservr.exe is available for SNA Server 2.11; the update supports a new registry parameter to correct this problem. This update is newer than SNA Server 2.11 Service Pack 1.

Once you have applied this update, you must also add the following registry entry. This will cause SNA Server to respond to the downstream client connection request. To add the registry entry:

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall Windows NT. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

Start Registry Editor (Regedt32.exe).

Under the HKEY_LOCAL_MACHINE subtree, go to the following subkey:

      SYSTEM\CurrentControlSet\Services\SnaServr\Parameters

Tab to the right-hand window and press the <Insert> key. In the Add Value dialog box, type:
Value Name: SHORTACTLU Data Type: REG_SZ
and click OK.
In the String Editor dialog box, type:
String: <any value>
Once entered, the value will appear in REGEDT32 as follows:
SHORTACTLU: REG_SZ: <any value>
Quit Registry Editor.

The SHORTACTLU registry entry causes SNA Server to respond to the downstream client connection request the above behavior, regardless of the value the entry is set to. When this registry entry is present, SNA Server sends a NOTIFY(available) to the host when it receives a short ACTLU response from the downstream client.

STATUS

Microsoft has confirmed this to be a problem in SNA Server versions 2.0, 2.1, 2.11, and 2.11 Service Pack 1 (this feature is implemented in 3.0). A supported fix to 2.11 is now available, but has not been fully regression- tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.