Host TPX Application Problem Leads to 3270 Emulator 2004 Error

• Microsoft SNA Server for Windows NT, versions 2.0, 2.1, and 2.11

SYMPTOMS

When you use TPX version 4.0.03 on an IBM MVS system (MVS v5.1 and VTAM v4r2), you will get the following Windows NT application event log entry indicating a 3270 emulation error using SNA Server and Wall Data Rumba.

   Event 21
   Negative response sent on connection <value> (SENSE = 2004)

NOTE: If this specific problem occurs, it would occur with any 3270 emulator. To confirm this is the problem, SNA Server DLC and 3270 message traces should be captured.

CAUSE

The TPX host application sends a message to the 3270 emulator when it did not have the direction flag. An SNA Server DLC message trace shows the following message sequence:

SNA Server     Host (TPX)

         <- BIND (appname = "TPX")

         <- SDT

RQE FMD BC EC DR1 BB CD -> (User Request)

         <- RQE FMD BC EC DR1 CD
            (TPX response)

(second part) EBIU ->

         <- RQE FMD BC EC DR1 CD
            (TPX response)

         <- RQE FMD BC EC DR1 EB
            (NCCF NETVIEW screen data)

In the above flow diagram, the TPX application sends an FMD message (the NCCF Netview screen) after it is already sent the Change Direction flag on the previous message. This is an SNA protocol violation that causes SNA Server to send a 2004 error (direction error).