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Q276045: Telnet IP+DM Is Ignored If TN3270 Server Is Already Queuing Data

Article: Q276045
Product(s): Microsoft SNA Server
Version(s): 3.0 (all SP),4.0,4.0 SP1,4.0 SP2,4.0 SP3
Operating System(s): 
Keyword(s): kbSNA400sp4fix kbSNA400PreSP4fix
Last Modified: 11-JUN-2002

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The information in this article applies to:

- Microsoft SNA Server, versions 3.0 SP1, 3.0 SP2, 3.0 SP3, 3.0 SP4, 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3 
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IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

  Q256986 Description of the Microsoft Windows Registry

SYMPTOMS
========

If you use the Rumba TN3270 client, the emulator may stop responding (hang) when
it is used with the TN3270 Server to access a host application.

If a network analysis tool, such as Microsoft Network Monitor, is used to capture
a network trace of the TCPIP traffic between the TN3270 client and TN3270
Server, this problem may occur after the client sends an Interrupt Process (IP)
and Data Mark (DM) message sequence (FFF4FFF2) in the inbound data stream.

Network Monitor frame illustration:

  + Frame: Base frame properties
  + ETHERNET: ETYPE = 0x0800 : Protocol = IP:DOD Internet Protocol
  + IP: ID = 0x7CC1; Proto = TCP; Len: 44

  TCP: .AP..., len: 4, seq:60113-60117, ack: 84013, win: 7744, src: 1097 dst:
  23 (TELNET)
  TCP: Source Port = 0x0449
  TCP: Destination Port = Telnet
  TCP: Sequence Number = 60113 (0xEAD1)
  TCP: Acknowledgement Number = 84013(0x1482D)
  TCP: Data Offset = 20 (0x14)
  TCP: Reserved = 0 (0x0000)
  TCP: Flags = 0x18 : .AP...

  TCP: ..0..... = No urgent data
  TCP: ...1.... = Acknowledgementfield significant
  TCP: ....1... = Push function
  TCP: .....0.. = No Reset
  TCP: ......0. = No Synchronize
  TCP: .......0 = No Fin

  TCP: Window = 7744 (0x1E40)
  TCP: Checksum = 0x7502
  TCP: Urgent Pointer = 0 (0x0)
  TCP: Data: Number of data bytes remaining = 4 (0x0004)

  TELNET: To Server From Port = 1097
  TELNET: Telnet Command = IAC IP(INTERRUPT PROCESS)
  TELNET: Telnet Command = IAC DM (DATA MARK)

  00000: 00 00 0C 07 AC 02 00 C0 4F 61 6B 94 08 00 45 10
  00010: 00 2C 7C C1 40 00 80 06 98 BC 9D CB A3 8C 9D CB
  00020: 06 1B 04 49 00 17 00 00 EA D1 00 01 48 2D 50 18
  00030: 1E 40 75 02 00 00 FF F4 FF F2

CAUSE
=====

The problem is that TN3270 client emulators can send data or, as in this case, a
function key (PA1 key), when the client does not have direction on the session
flow.

To enable TN3270 clients to work in this manner and to avoid a TN3270 session
protocol violation error, SNA Server internally queues such data until the
client is granted direction on the session and can legitimately send inbound
data.

In this instance, however, after the client's illegal PA1 key is queued, the
TN3270 Server subsequently fails to process the following IP-DM sequence. This
is because the TN3270 Server adds it to the queue of data for later inbound
transmission to the host when the client is granted direction on the session
flow. As a result, no SIGNAL is sent, which typically is expected when an IP
command is processed.

RESOLUTION
==========

To resolve this problem, obtain the latest service pack for SNA Server 4.0. For
additional information, please see the following article in the Microsoft
Knowledge Base:

  Q215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack



STATUS
======

Microsoft has confirmed this to be a problem in Microsoft SNA Server version 4.0
(all Service Packs).

This problem was first corrected in SNA Server 4.0 Service Pack 4.

MORE INFORMATION
================

The TN3270 Server has been enhanced so that it no longer tries to act as a
broker to resolve protocol ambiguities between the TN3270 client and host. The
DisableDataQueuing registry option, which turns off queuing of data by the
TN3270 Server, has been implemented as follows:

WARNING: If you use Registry Editor incorrectly, you may cause serious problems
that may require you to reinstall your operating system. Microsoft cannot
guarantee that you can solve problems that result from using Registry Editor
incorrectly. Use Registry Editor at your own risk.

1. Start Registry Editor (Regedt32.exe).

2. Locate the following key in the registry:

  HKEY_LOCAL_MACHINE\System\CCS\Services\TN3270\Parameters

NOTE: This registry key is one path; it has been wrapped for readability.

3. On the Edit menu, click Add Value, and then add the following registry value:

  Value Name: DisableDataQueuing
  Data Type: REG_EXPAND_SZ
  Value: YES

4. Quit Registry Editor.

This registry option is a generic solution to problems that are caused by clients
that are not working correctly (sending data when they don't have direction)
and/or hosts that are not working correctly (failing to lock the client's
keyboard appropriately through the WCC byte).


Additional query words: sp1 sp2 sp3

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Keywords          : kbSNA400sp4fix kbSNA400PreSP4fix 
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ400 kbSNAServ300SP3 kbSNAServ300SP1 kbSNAServ400SP1 kbSNAServ400SP2 kbSNAServ400SP3 kbSNAServ300SP2 kbSNAServ300SP4
Version           : :3.0 (all SP),4.0,4.0 SP1,4.0 SP2,4.0 SP3
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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