Exchange X.400 MTA over TP4 Sends Only 2 Queued Messages, Stops (159185)

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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.