3270 Sessions Unexpectedly Return to SSCP Screen

• Microsoft SNA Server for Windows NT, versions 2.0, 2.1, 2.11, and 3.0

SYMPTOMS

SNA Server clients using 3270 display sessions are returned to the SSCP (VTAM Signon) screen unexpectedly while actively working in a host application. The SNA Server may log one or more of the following events in the Windows NT Application Event Log when this problem occurs:

   Event ID: 4
   Source: SNA Server
   Description: (1133) Message Sequence Error

   EXPLANATION
   The SNA server (node) received an invalid or unexpected message from a
   remote node on an SNA session. The remote system has a possible
   configuration or internal logic error.

   SUBCODE INFORMATION
   X'1133'  The node received a request with an invalid sequence number.

   Event ID: 12
   Source: SNA Server
   Description: (1118) Negative Response from Remote System (SENSE = 200D)

   SUBCODE INFORMATION
   X'1118'  The local SNA server (node) received an SNA negative response
   on an SNA session from a remote system, which indicates a protocol
   violation by the 3270 emulator. The SNA sense code shown gives details
   of the type of error. See "IBM Systems Network Architecture: Formats"
   for an explanation of the sense code.

   Event ID: 13
   Source: SNA Server
   Description: (1141) Message Sequence Error (SENSE = 2001)

   EXPLANATION
   The SNA server (node) received an invalid or unexpected message from a
   remote node during an SNA session. The cause is probably a logic error
   in the remote system. The SNA sense data shown gives details of the type
   of error.

   SUBCODE INFORMATION
   X'1141'  Session-level protocol violation in an SNA message from the
   partner
   LU.

CAUSE

This has only been reported on SNA Servers with 802.2 connections to IBM 3174 Control Units on Ethernet networks. The problem occurs because a 3174 Ethernet gateway may send a duplicate SNA sequence number to the SNA Server when the 3174 is handling an SNA frame between 1490 and 1493 bytes in size. This leads to a condition where a frame may be re-sent by the 3174 causing the symptoms discussed previously. In addition, the problem only occurs if the 3174 is running 3174 Microcode Level C6.1 or C6.2.

RESOLUTION

A fix for this problem is available from IBM. Contact IBM support and request IBM 3174 PTR #B27E.

MORE INFORMATION

For information about how to contact IBM, query in the Knowledge Base for one of the following articles:

   ARTICLE-ID: Q65416
   TITLE     : Hardware and Software Third-Party Vendor Contact List, A-K

   ARTICLE-ID: ID: Q60781
   TITLE     : Hardware and Software Third-Party Vendor Contact List, L-P

   ARTICLE-ID: Q60782
   TITLE     : Hardware and Software Third-Party Vendor Contact List, Q-Z