IBM PC/3270 for NT v4.1 TN3270 May Fail with XPROG750

MORE INFORMATION

The IBM PC/3270 TN3270E emulator was not properly handling a NULL RU arriving on an LU-LU session from a host application. The following annotated SNA Server TN3270 internal trace illustrates the problem.

1. Host sends Request Definite Response (RQD) message with null RU:

      >04/16 12:56:10.333 (+150 msecs)  Event=TEV_DataFromSNAAsync
       Thread = 0x00000139  Session = 0x0018F248  Socket = 0x000005D8
       VCB address=0x0018F41C
       verb_length=0x0044  verb=0x0052 (RUI)  opcode=0x8003 (READ)
       sid=0x00010003  correlator=0x0018F248  post_handle=0x000005C0
       prim_rc=LUA_OK  sec_rc=LUA_SEC_RC_OK
       lu_norm    lua_data_length=0x00000000
       lua_message_type=0x01 (LUA_MESSAGE_TYPE_LU_DATA)
       TH Only    efi=0  oadi=0  daf=FE  oaf=01  snf=0003
       RH  REQ FMD fi=0   sdi=0  bci=1  eci=1  (Only)
       03 80 80    dr1=1  dr2=0  ri=0   qri=0  pi=0
                   bbi=1  ebi=0  cdi=0  csi=0  edi=0  pdi=0
   						

2. SNA Server TN3270E server sends this message to the TN3270E client. Note the TN3270E header:

      data type       = 00 (3270 data request)
      request flag    = 00
      response flag   = 02 (always response)
      sequence number = 0001
      IAC EOR = ff ef
   
      >04/16 12:56:10.333 (+ smidgen )  Event=TEV_TCPSendIssued
       Thread = 0x00000139  Session = 0x0018F248  Socket = 0x000005D8
       Number of bytes = 7
         TN3270E message = 0000 0200 02ff ef 
   						

3. At this point, the IBM PC/3270 emulator displays "XPROG750". If the user enters <3270 Reset> and attempts to send a new request on the session, the request is received by the TN3270E server:

      >04/16 12:57:06.594 (+ smidgen )  Event=TEV_DataFromClient
       Thread = 0x00000139  Session = 0x0018F248  Socket = 0x000005D8
       000000  0000 0000 037d 405a 5c5c 8183 98a4 8999  |.....' !..acquir|
       000010  854b 6b86 9683 f9f8 f3f0 f56b 9996 a4a3  |e.,foc98305,rout|
       000020  8599 ffef                                |er..            |
   						

4. However, since the previous Definite Response request was never acknowledged by the IBM PC/3270 emulator, this new user request is ignored by the SNA Server TN3270E Server (as indicated by the "Ignore" below):

      >04/16 12:57:06.594 (+ smidgen )  Event=TEV_CRTFirstInboundByte
       Thread = 0x00000139  Session = 0x0018F248  Socket = 0x000005D8
       Ignore
       State = OPER        InputState = IDLE        OutputState = SNARESP
       Toggle = LU-LU       LU State = RCV         CanQueue = YES
       Bracket = INB         DTActive
   						

By configuring the SNA Server TN3270E Server to use "TN3270 mode only", this forces the negotiation of the TN3270 protocol when communicating with the IBM PC/3270 TN3270 emulator, rather than TN3270E. The problem does not occur with the IBM PC/3270 emulator when using TN3270 protocol.

Contact IBM PC/3270 technical support for a fix to IBM PC/3270, referring to the APAR numbers mentioned in the SUMMARY section above.

TROUBLESHOOTING EVENT 306 ERRORS

The TN3270 Server Event 306 message indicates that the TN3270 Server "ignored" a request from a TN3270/TN3270E client emulator. This can occur if:

1. The TN3270E client has not acknowledged a previously sent request.
   
   -or-
2. The host has direction to send on the SNA session, so a new TN3270 user request cannot be issued.

To track down the exact cause of the Event 306 error, an SNA Server TN3270 Internal trace should be captured. This can be captured as follows:

If SNA Server 2.11 is being used:

1. Start the TN3270 Service Admin program on the server.
2. Choose the <Trace> option.
3. Select the "Active" checkbox, and then <OK>.
4. Capture the problem.
5. Once captured, disable tracing by deselecting the "Active" checkbox and choosing <OK>.
6. The traces can be found in the \TN3270\TRACES directory, called TN3_00.TRC (and increment through TN3_09.TRC).

If SNA Server 3.0 is being used:

1. Start the SNATRACE program on the server.
2. From the Trace Items folder, double-click on the "TN3270" server.
3. Focus on the "TN3270 Internal Trace" folder and choose the checkbox for "TN3270 Internal Trace", and then the <Apply> option.
4. Capture the problem.
5. Once captured, disable tracing by selecting the "Clear All Traces" option from the Trace Items folder.
6. The traces can be found in the \SNA\TRACES directory, called TN3_00.TRC (and increment through TN3_09.TRC).