RUI Interface Enhancement to Avoid Duplicate Signon Screens (107384)

SUMMARY

If an SLI_OPEN follows immediately after an SLI_CLOSE statement the SSCP Welcome message screen may appear twice under some certain timing conditions.

An SNA Server 2.11 update is available which closes a timing window where this can occur. For additional information, please see the following article in the Microsoft Knowledge Base:

137482 LUA Program Receives Host Sign-On Screen Twice and then Hangs

However, with this update applied, this problem can still occur under certain timing conditions described in this article.

An Additional Update Is Available

Another update to SNA Server 2.11 now supports the ability to put a small configurable delay between the SLI_CLOSE completion and issuing the new SLI_OPEN statement. Microsoft has updated the following file to include this feature:

<snaroot>\system\WINRUI32.DLL

This update is for Win32 clients only and is implemented in the WIN32 RUI Interface and exported as a new registry value.

Implementing the Update

To set this delay you have to obtain the update and add the new registry value INITDELAY under the HKEY_LOCAL_MACHINE subtree under the following subkey:

   SYSTEM\CurrentControlSet\Services\SnaBase\Parameters\Client

Use the following information when adding the new value:

   Value Name: INITDELAY
   Data Type:  REG_DWORD
   Data:       0-10 (decimal)

   Default:    0 seconds

This variable sets an optional delay in seconds in processing RUI_INIT requests. If you do not specify an entry for data, there is no delay. If you configure a value greater than 10, then a value of 10 is used.

MORE INFORMATION

When an LUA session is closed and immediately reopened, the SNA Server may resend the host SSCP welcome message twice to the LUA application. The following diagram explains what is happening:

Message flow as the node sees it.       Message flow as the host sees it.
    Host                Node                Host             Node
    ====                ====                ====             ====

      NOTIFY unavailable                      NOTIFY unavailable
        (SLU disabled)                         (SLU disabled)
     <--------------------                   <----------------

          NOTIFY +rsp                           NOTIFY +rsp
     -------------------->                   ----------------->

        NOTIFY available                        logon banner
     <--------------------                   ----------------->

        logon banner                           NOTIFY available
                                                (SLU enabled)
     -------------------->                   <-----------------

        NOTIFY +rsp                             NOTIFY +rsp
     -------------------->                   ----------------->

        logon banner                            logon banner
     -------------------->                   ----------------->

When the host receives the first NOTIFY it sends a logon screen. At the same time, the node is sending the second NOTIFY. In this case by the time that the logon screen reaches the node, the node has passed on the second NOTIFY to the link service. In that situation the node is not able to determine whether the logon screen was sent due to the first NOTIFY, or the second NOTIFY, and so it passes it up to the application. Shortly thereafter, the second logon screen arrives, and the node also passes that up to the application.

This is because the underlying SSCP-LU session on which the NOTIFYs and the logon screens flow is not brought down when the SLI session is brought down and a new SLI session is started. Therefore, the node cannot tell that a particular message on the SSCP-LU session is associated with the SLI session which has been terminated.

STATUS

This feature is included in the latest U.S. Service Pack for SNA Server for Windows NT, version 2.11. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

This feature is also included in SNA Server versions 3.0 (all Service Packs) and 4.0.