Function Management Interface

The Function Management Interface (FMI) provides applications with direct access to SNA data flows and information about SNA control flows by means of status messages, while shielding the application from the full complexities of SNA protocol handling. FMI is particularly suited to the requirements of applications emulating 3270-type controllers. The FMI is defined in terms of the messages that are sent across the interface. This is logically distinct from the definition of the DL-BASE/DMOD interface, which defines the mechanism for sending messages between two components in Microsoft SNA Server.

The FMI is used by logical unit (LU) types 0, 1, 2, and 3, but not by LU type 6.2. It provides access to the system service control point logical unit (SSCP-LU) session as well as the main primary LU-secondary LU (PLU-SLU) session. An application can use the FMI to access multiple sessions, and hence multiple LUs, simultaneously. The 3270 emulator on the client communicates over the LAN with the local node on the server computer by exchanging messages. The content and format of the messages are defined by the FMI.

An application using the FMI can communicate on three SNA sessions:

• The SSCP session, which defines access between the SNA Server secondary LU and the host SSCP.
• The PLU session, which defines access between the SNA Server LU and a PLU (primary LU) in the host.
• The PU-SSCP session which defines access between the physical unit (local node) and the host SSCP.

Developers should be aware of other important FMI issues, such as protocol structure and status messages.