68 Implementing and Managing APPC Protected Conversations
5.1 Description
For IMS-to-IMS APPC protected conversations we wanted to test the interaction between two
IMS application programs running in two different IMS systems. We wanted to verify actions
taken for normal processing and for failure scenarios. IMS requires APPC/MVS and MVS
Recoverable Resource Management Services to enable APPC protected conversations.
APPC/IMS is an APPC/MVS scheduler that supports implicit and explicit APPC application
programming. An implicit application program uses IMS DL/I message calls for the
communication interface and APPC/IMS provides the interaction with APPC. This means that
existing IMS applications are able to participate in an APPC environment without
modification.
An explicit application uses APPC calls for direct interaction with an APPC partner program.
IMS supports the following explicit application programs:
򐂰 Modified Standard
򐂰 CPI-C Driven
The Modified Standard application program uses a combination of IMS DL/I message calls
and the APPC calls to communicate directly with APPC/MVS as shown in Figure 5-1.
Figure 5-1 Sample of modified standard application program
An IMS Modified Standard application program can initiate an APPC Protected Conversation;
however, APPC/IMS has to initiate the coordinated syncpoint process. When the IMS
Modified Standard application program Deallocates the protected conversation, the APPC
conversation is in a Defer-Deallocate state. The IMS syncpoint manager recognizes that
APPC/MVS has expressed interest in the Context and Unit of Recovery associated with the
GU I/O PCB
Allocate
Send
Send
Receive
Send
Deallocate
Access IMS DB
Access DB2
ISRT I/O PCB
Modified Standard
Chapter 5. Sample scenario: IMS to IMS 69
IMS Modified Standard application program. At the start of the IMS syncpoint process IMS
will issue the ATRCMIT call to RRS to initiate the coordinated syncpoint process. The Partner
Program will be notified to issue a Commit when it Receives Take_Commit_Deallocate.
RRS is the syncpoint coordinator that drives Two-Phase commit flows to IMS and to
APPC/MVS. APPC/MVS provides the Communication Resource Manager support to flow
Two-Phase commit protocols using the protected conversation as shown in Figure 5-2.
Figure 5-2 Syncpoint flow
IMS only schedules a CPI-C Driven application program and the application program has to
issue the X/OPEN CPI-C calls or the APPC/MVS-specific API calls to communicate with the
APPC partner program, as illustrated in Figure 5-3 on page 70.
APPC/IMS
ATRCMIT
IMS Modified
Application
GU
Allocate
Send
Send
Receive
Deallocate
ISRT
APPC Partner
Accept
Receive
Receive
Send
Receive
Take-Commit_Deallocate
SRRCMIT
Deallocate
APPC/MVS
RRS
Syncpoint Flows
70 Implementing and Managing APPC Protected Conversations
Figure 5-3 CPI-C Driver application flow
An IMS CPI-C Driven application program uses SRRCMIT to participate in an APPC
protected conversation coordinated syncpoint process. When the IMS CPI-C Driven
application program receives Take_Commit on a Receive verb, it uses SRRCMIT to activate
its syncpoint. In the case of Take_Commit_Deallocate the IMS CPI-C Driven application
program issues the SRRCMIT call and Deallocates the protected conversation.
Our sample IMS PL/I application programs consisted of the following:
IMSH IMSI
IMS1TR1
Modified
IMS2IMP Implicit
IMS1TR2
Modified
IMS2EXP Explicit
Note: To re-create the environment we used:
Refer to Appendix A, “Installation definitions for Protected Conversation exploiters” on
page 113 for detailed installation instructions required to set up the sample systems used
throughout this book.
Refer to Appendix B, “APPC exploiter sample source code” on page 155 for the source
code used in our examples.
CPI
CPI
-
-
C Driven
C Driven
Accept
Receive
Receive
Access IMS DB / DB2
Send
Receive
Take_Commit
SRRCMIT
Receive
Take_Commit_Deallocate
SRRCMIT
Deallocate

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