Request and response exchanges for typical communication operations
This appendix contains diagrams that show the sequences
in which requests and responses are exchanged to perform typical data
communication operations using VTAM®.
The diagrams can be useful in coding application programs that perform
the operations.
Note: A PLU application program is a VTAM application program that acts
as the PLU in the session, and an SLU application program is
a VTAM application program
that acts as the SLU in the session.
Figure 1 through Figure 21 are oriented primarily toward communication
between a PLU application program and a device-type logical unit,
although some of these diagrams apply also when the SLU is a SLU application
program. In Figure 1 through Figure 21, the “reads” and “writes” shown in the
“Logical Unit” column represent logic that can be performed by a control
program in the logical unit, a user-written program that operates
in the logical unit, or both. It is a general representation of the
input and output from the logical unit. The PLU application program's
side of the exchange is shown in more detail.
Figure 22 through Figure 36 are oriented toward operations between
a PLU application program and a SLU application program.
Figure 37 and Figure 38 illustrate a session between the VTAM SSCP and an application program
over the CNM interface.
In any diagram showing a negative response being sent
to an application program, a SYNAD exit routine might be scheduled
with an exception condition return code. SYNAD exit routines are not
illustrated in this appendix. See Coding LERAD and SYNAD exit routines for
details. Figure 1. Device-type LU initiates and establishes
a session with a PLU application program.
For initiating and establishing a session from a SLU application
program, see Figure 22 and Figure 23. Figure 2. PLU application
program acquires (initiates and establishes) a session with a device-type
LU.
For initiating a session from a PLU to a SLU application program,
see Figure 24 and Figure 25.
Figure 3. After a warm start, a PLU application
program reestablishes a session and resynchronizes sequence numbers
(Part 1 of 2)
Figure 4. After a warm start, a
PLU application program reestablishes a session and resynchronizes
sequence numbers (Part 2 of 2)
Figure 5. PLU application program and a secondary
logical unit exchange data (Part 1 of 3)
Figure 6. PLU application program and a secondary
logical unit exchange data (Part 2 of 3)
Figure 7. PLU application program and a secondary
logical unit exchange data (Part 3 of 3 about sections A, B, C and
D)
A
With no responses
B
With negative responses only if an exception occurs
C
With definite response 1 (positive or negative)
D
With definite responses 1 and 2 sent at the same time.
Figure 8. Logical unit sends a chain of
data to the PLU application program
A
Without a negative response
B
With a negative response.
Figure 9. Application program and logical
unit use quiesce protocol
A
The application program quiesces the logical unit
B
The logical unit quiesces the application program.
Figure 10. Application program and logical
unit use bracket protocol (Part 1 of 2)
Figure 11. Application program and logical unit
use bracket protocol (Part 2 of 2)
A
Where the logical unit begins the bracket
B
Where the PLU application program begins the bracket
C
Where the PLU application program gets a positive response to
its BID and begins the bracket
D
Where BID produces a later Ready-to-Receive request.
For more details on using brackets with a SLU application
program, see Figure 28 and Figure 29.
Figure 12. Application program and logical unit
use change-direction protocol
A
Where only change-direction indicators are used
B
Where in addition, the Signal request (requesting change direction)
is used.
Figure 13. PLU application program resynchronizes
sequence numbers with the logical unit.
For resynchronization of sequence numbers between PLU
and SLU application programs, see Figure 26 and Figure 27. For the dialog between the PLU application
program and the logical unit to establish sequence numbers, see steps
2–9 in Figure 3 and Figure 4.
(Use STSN and any dialog at your own discretion.)
Figure 14. Application program and logical unit
use the signal request
A
Sent by the logical unit
B
Sent by the PLU application program.
Figure 15. Application program and logical unit
use the LUSTAT request
A
Sent by the logical unit
B
Sent by the application program.
Figure 16. Operations are shut down in an orderly
fashion
A
The logical unit requests shutdown
B
The PLU application program orders shutdown.
Figure 17. Logical unit terminates a session.
For termination requests from a SLU application program,
see Figure 30 and Figure 31.
Figure 18. PLU application program terminates
a session with the logical unit.
