Telnet IP+DM Is Ignored If TN3270 Server Is Already Queuing Data (276045)

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:

256986 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

SNA Server 4.0

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

215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack

Host Integration Server 2000

To resolve this problem, obtain the latest service pack for Host Integration Server 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

328152 How to Obtain the Latest Host Integration Server 2000 Service Pack

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.

Start Registry Editor (Regedt32.exe).
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.
On the Edit menu, click Add Value, and then add the following registry value:
Value Name: DisableDataQueuing
Data Type: REG_SZ
Value: YES
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).