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.
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:
- Each FEPI outbound request causes the generation of an RPL. This RPL lasts
only for the duration of the FEPI request.
- Each FEPI node has a "Receive-Any" RPL. When an inbound flow occurs,
this RPL is attached to the FEPI connection, and turned into a "Receive-Specific" RPL.
When the flow has been received, a new "Receive-Any" RPL is generated
and attached to the node.
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:
- The failure of a process that was responded to positively
- A session outage
- The receipt of network service RUs.
- SCIP
- Processes the receipt of session-control requests.
- TPEND
- Processes the termination of VTAM.
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