Exchange X.400 MTA over TP4 Sends Only 2 Queued Messages, Stops

• Microsoft Exchange Server, version 4.0

SYMPTOMS

The Microsoft Exchange Server message transfer agent (MTA) configured with an X.400 Connector over TP4, (1988, monolog) to a foreign X.400 MTA, only transmits two queued messages and fails to send more. Additionally, the association between MTAs will not be released.

CAUSE

Expedited data at the transport layer is being improperly handled by components of Winsock and the TP4 protocol driver, Afd.sys and Isotp.sys respectively.

WORKAROUND

To work around this problem:

• Configure the foreign MTA’s TP4 (OSI) stack to disable or refuse the use of Transport Expedited Data during transport session negotiation of the association between the MTAs.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 3.5x. A supported fix is now available, but has not been fully regression-tested and should be applied only to systems experiencing this specific problem. This is a post-SP5 fix. No additional official service packs are planned for Windows NT 3.51. Contact Microsoft Technical Support for more information.

MORE INFORMATION

Transport Expedited Data is a special feature of the transport portion OSI protocol that allows a frame to have a "higher priority" on the network. It is the intention that this frame would be processed (up the stack) before other pending, but non-expedited frames. It is typically used to signal th t an important and timely change is requested, or about to occur (For instance, a user hits Ctrl-C on a terminal to signal the other side to cancel the previous request and return control to the user. The Ctrl-C may be sent in an expedited’ frame if the application was coded to do so, and expedited data support was negotiated by the transport layer).

Microsoft Exchange Server has a "Use Expedited data" check box in the X.400 Connector’s Stack property page. This specifies only whether the MTA will send data via expedited transport frames (if that service has been negotiated by the transport for the current association). The MTA does not respond any differently to incoming data that has arrived via expedited transport frames than it does to regular data, nor does selecting this check box change the Windows NT TP4 stack behavior.

The Exchange X.400 MTA, when viewed as an OSI application, does not configure or directly influence network features of any layer below the Session layer of the OSI model. The Windows NT TP4 transport layer was designed to negotiate for the use of expedited data, but to honor a refusal of that feature when initiating a session. When responding to session establishment requests, the Windows NT TP4 transport layer accepts whatever the initiating side requests with regard to expedited data. There is no way to override or force the Windows NT TP4 transport layer to require or deny the use of transport expedited data.