RUI Problem Handling RUI_SEND After Sense Data Received

• Microsoft SNA Server for Windows NT, versions 2.1 and 2.11

SYMPTOMS

If the host application sends sense data to an RUI application while the RUI application is sending data, the SNA Server RUI library queues the application data in error and never sends it, causing the RUI application and the host application to become unsyncronized.

CAUSE

The RUI application gets the sense data indicator (SDI) message and correctly sends negative response. Because the RUI library is in the middle of a chain (it has only received Begin Chain - BCI, not End Chain - ECI) it sets a flag telling it to discard all data messages until it receives one with ECI set. Unfortunately the server performs the same check. Therefore the RUI library does not see the ECI flag until it receives the end of the NEXT chain (the retried one).

RESOLUTION

The RUI application can't work around this problem. The solution is for the RUI library to detect that a new chain is starting without the purging one ending, and simply to stop purging at that point.

An update to the SNA Server RUI DLL corrects this problem. Note that with this update applied, the RUI application will still miss the Middle of Chain (MC) and EC sequence numbers on the rejected chain. Microsoft has updated the following files to correct this problem:

   Client Platforms     Updated Files
   -----------------------------------------------------------
   Win32                <snaroot>\system\WINRUI32.DLL
   Windows 3.x          <winroot>\system\WINRUI.DLL
   OS/2                 <snaroot>\ACSRUI.DLL

STATUS

Microsoft has confirmed this to be a problem in SNA Server for Windows NT. This problem was corrected in the latest SNA Server for Windows NT, 2.11 U.S. Service Pack. 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