KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q225207: APPC/CPIC App Unable to Allocate Conversation over Dependent LU

Article: Q225207
Product(s): Microsoft SNA Server
Version(s): WINDOWS:3.0SP3,4.0SP1,4.0SP2
Operating System(s): 
Keyword(s): kbsna400sp3fix
Last Modified: 08-MAY-2002

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft SNA Server, versions 3.0SP3, 4.0SP1, 4.0SP2 
-------------------------------------------------------------------------------


SYMPTOMS
========

An APPC or CPI-C application may fail to get an active conversation with a
remote APPC LU if a previous conversation with a different remote APPC LU using
the same dependent local APPC LU has ended. For example, if there was a
conversation over a dependent local LU, "LOCAL," and a remote LU, "REMOTE1," an
APPC or CPI-C application may fail to get an active conversation over dependent
local LU "LOCAL" and remote LU "REMOTE2" even if the previous conversation has
ended.

When this occurs, the APPC or CPI-C application call to [MC_]ALLOCATE or CMALLC
never completes. If the application does not use a timeout, the ALLOCATE will
appear to hang since the call does not complete. If the application does have a
timeout, the timeout will cancel the outstanding ALLOCATE, and return an error.

For additional information about a related problem in earlier versions of SNA
Server, please see the following article in the Microsoft Knowledge Base:

  Q180416 APPC or CPI-C TPs May Fail When Using Dependent LU 6.2 Sessions

NOTE: This problem can only occur when using Dependent LU 6.2 sessions and does
not occur when using Independent LU 6.2 sessions.

CAUSE
=====

A similar problem was corrected in earlier versions of SNA Server as described
in article Q180416. SNA Server was modified to send an UNBIND Cleanup to the
host to end the previous session that is no longer being used. In this case, the
UNBIND Cleanup is treated as an error by the CICS Region on the host, so CICS
attempts to re-establish the session over the local APPC LU/remote APPC LU that
was previously being used. CICS sends a BIND to the SNA Server to re-establish
this session. SNA Server responds with a BIND +RSP, which causes the ALLOCATE
for the new session over the same local APPC LU and a different remote APPC LU
to hang because the local APPC LU is already in use.

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


STATUS
======

Microsoft has confirmed this to be a problem in Microsoft SNA Server versions
3.0 SP3, 4.0 SP1, and 4.0 SP2. This problem was first corrected in SNA Server
version 4.0 Service Pack 3.

MORE INFORMATION
================

After applying the update, SNA Server will issue an UNBIND Normal to end the
previously used session instead of an UNBIND Cleanup. This is not treated as an
error by CICS on the mainframe, so it will not attempt to re-establish the
previous session.

This problem only occurs with dependent LU 6.2 LUs because they can only support
one concurrent session at a time. Independent LU 6.2 LUs can support multiple
parallel sessions concurrently, so a new session request to a different remote
LU can be fulfilled without ending the previous session.

The following is a sequence of events that can lead to this problem assuming the
following APPC LUs are defined in the SNA Server configuration:

Local APPC LU: LOCAL (defined as a dependent LU 6.2 LU)
Remote APPC LU: REMOTE1
Remote APPC LU: REMOTE2
APPC Mode: APPCMODE

1. An APPC or CPI-C application successfully establishes a session over the
  following APPC triplet: LOCAL/REMOTE1/APPCMODE.

2. The application executes a transaction over the previously established
  session and ends the conversation.

3. An APPC or CPI-C application requests a session over the following APPC
  triplet: LOCAL/REMOTE2/APPCMODE.

4. SNA Server issues an UNBIND Cleanup to end the original session established
  in Step 1.

5. SNA Server sends an INITSELF command to the host to solicit a BIND for the
  new session over LOCAL/REMOTE2/APPCMODE.

6. The host responds with an INITSELF +RSP for this new session request.

7. The host then sends a BIND to re-establish the original session over
  LOCAL/REMOTE1/APPCMODE.

8. At this point, the requested session over LOCAL/REMOTE2/APPCMODE cannot start
  until the original session is ended. This causes the ALLOCATE to be queued
  such that it appears to hang or timeout depending on the APPC/CPI-C
  application.


Additional query words:

======================================================================
Keywords          : kbsna400sp3fix 
Technology        : kbAudDeveloper kbSNAServSearch
Version           : WINDOWS:3.0SP3,4.0SP1,4.0SP2
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.