FEPI and VTAM

This section outlines how FEPI interacts with VTAM®, and discusses VTAM control blocks and exits.

You should refer to the OS/390 eNetwork Communications Server: SNA Programming manual for all information relating to VTAM programming.

VTAM control blocks

FEPI uses standard VTAM programming facilities for its communication. The way in which VTAM control blocks interact with FEPI control blocks is as follows:

ACBs
Each FEPI node represents a terminal connected to the partner system. Consequently, each node has an access control block (ACB). This ACB is opened when the node is acquired, and closed when the node is released.
NIBs
Each FEPI target contains the applid of the back-end system. This is used to build a node initialization block (NIB), when a connection is acquired by issuing a VTAM REQSESS request. In common with CICS® data communication, the "confidential" flag is set off.
RPLs
There are two types of request parameter list (RPL) used by FEPI:

VTAM exits

FEPI communicates with VTAM as asynchronously as possible. Therefore, VTAM exits are extensively used for FEPI communication. The following VTAM exits receive control at specific stages of the communication process:

DFASY
Processes the receipt of expedited-data-flow control indicators.
LOGON
Processes the receipt of a CINIT in which FEPI is acting as the primary logical unit (PLU).
LOSTERM
Processes the loss of a session.
NSEXIT
Processes:
SCIP
Processes the receipt of session-control requests.
TPEND
Processes the termination of VTAM.
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