SNA Server Support for ACTPU (ERP) and ACTLU (ERP)

 Last reviewed: October 29, 1997
Article ID: Q138469
The information in this article applies to:
  • Microsoft SNA Server for Windows NT, versions 2.0, 2.1, 2.11, and 3.0

SUMMARY

If you have more than one mainframe attached to your Front End Processor (FEP) the IBM SNA "error recovery protocol" (ERP) is used. The Systems Services Control Point (SSCP) is located on one mainframe (that controls activation of the SNA network by issuing ACTPU and ACTLUs) while the host applications may reside on another mainframe. The ERP protocol makes it possible to reboot the mainframe containing the SSCP without interrupting the application. So, when the mainframe comes back up, it issues an ACTPU (ERP) and ACTLU (ERP) command so that the user's application session (the PLU-SLU session) is not reset.

SNA Server supports the recovery of PLU-SLU sessions after receiving an ACTPU (ERP) and ACTLU (ERP) command. However, ACTPU (ERP) recovery requires that the SNA Server connection is not dropped. SNA Server reports connection failures by logging Event 23 in the Windows NT application event log. If the SNA Server connection to the FEP is lost, PLU-SLU session recovery is not possible.

MORE INFORMATION

SNA Server handles session recovery as follows, when receiving ACTPU and ACTLU commands:

  • When receiving an ACTLU (cold) command, SNA Server resets the SSCP-LU session (which is used to carry the logon screen) and the PLU-SLU session (used for applications and data transfer after the user has logged on to an application) if the PLU-SLU session is active.
  • When receiving an ACTLU (ERP) command, SNA Server resets the SSCP-LU session. If there is an active PLU-SLU session, this session is left active.
  • The ACTLU (ERP) command is used in conjunction with the ACTPU (ERP) command. As for ACTLUs, if a cold ACTPU is issued by the host, SNA Server resets all the sessions using that PU, which is all the 3270 sessions.
  • If an ACTPU (ERP) command is issued by the host, SNA Server only resets the PU-SSCP session.

The SNA Server will send back an ACTPU (ERP) +RSP if all of the following are true:
  • An ACTPU (ERP) request was received.
  • The ACTPU (ERP) was received when the PU-SSCP session was already active.
  • The ACTPUERP Registry entry is defined.

NOTE: Starting with SNA Server 2.11 Service Pack 2, the default behavior for SNA Server was changed so that ACTPU (ERP) support is not enabled by default. For more information on why the default behavior was changed, see the following Microsoft Knowledge Base article: 

   ARTICLE-ID: Q153253
   TITLE: SNA Server 3270 Sessions Not Recovered with Eicon WAN Server
Add the following Registry Entry to enable ACTPU (ERP) support in SNA Server:

  1. Start Registry Editor (Regedt32.exe or Regedit.exe, as appropriate for your version of Windows NT).
2. Go to the following key in the registry: 

   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\SnaServr\Parameters

  • On the Edit menu, click Add Value and use the following entry:

    Value Name: ACTPUERP Data Type: REG_SZ

  • Click OK. 5. In the String field, input the string TRUE and then click OK. (Actually, 
       any value can be entered for the String to enable ACTPU (ERP) support.)
    6. Exit the Registry Editor. 7. Stop and restart the SNA Server service.

    If the ACTPUERP registry entry is not set, SNA Server treats all ACTPU requests as ACTPU (Cold) requests.

    NOTE: For information describing the ACTPU and ACTLU message formats, see the IBM SNA Formats Guide (IBM p/n# GA27-3136), Chapter 5, "Request/Response Units (RUs)".

    • Additional query words: prodsna
    Keywords : sna3270 kbnetwork
    Version : 2.0 2.1 2.11 3.0
    Platform : WINDOWS

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    Last reviewed: October 29, 1997
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