Migration mode

In migration mode, the front-end and back-end transactions use LUTYPE6.1 commands just as if the session was an LUTYPE6.1 session. CICS® takes data from the transaction in the normal way, and formats it as an APPC mapped data stream for transmission over the link. At the receiving side, CICS analyses the APPC mapped data stream and presents the LUTYPE6.1 data and function management headers to the receiving transaction.

In general, you will not have to modify existing CICS-to-CICS ISC applications to enable them to run in migration mode on APPC links. A notable exception is the use of the ALLOCATE SESSION command. If your installation previously had individually defined ISC sessions, and your application used the ALLOCATE SESSION command to acquire a specific session, you must change this command to ALLOCATE SYSID.

The ISSUE SIGNAL command is valid for both LU types, but the WAIT SIGNAL command is available only for LUTYPE6.1.

Table 47 compares the commands that you can use for:

As Table 47 shows, migration mode allows you to start adding new function to an application (for example, using ISSUE ERROR or ISSUE ABEND) without converting it entirely to APPC. You can also implement different sync levels by modifying the application to use the CONNECT PROCESS command. Applications not modified to use CONNECT PROCESS will use sync level 2. The migration of an application towards the "pure" APPC level can thus be made stepwise.

To aid migration, the SESSION and CONVID options can be used interchangeably.

If a migration-mode transaction abends, the architected APPC flows take place. How this affects the connected transaction depends where the abend occurs and is often different from what you would expect if the connection were native LUTYPE6.1.

Because APPC uses different modules from LUTYPE6.1, the user exits XZCIN and XZCOUT are not taken for APPC sessions. Any programs making use of these exits on LUTYPE6.1 will need consideration.

Table 47. Migration of LUTYPE6.1 programs to APPC links
Operation Command LU6.1 Migration APPC
Obtain use of a session ALLOCATE SESSION yes no no
Obtain use of a session ALLOCATE SYSID yes yes yes
Build an LUTYPE6.1 attach FMH BUILD ATTACHID yes yes no
Start a partner transaction SEND yes(1) yes(4) no
Start a partner transaction SEND ATTACHID yes(2) yes(5) no
Start a partner transaction SEND FMH yes(3) yes(6) no
Start a partner transaction CONNECT PROCESS no yes(7) yes(7)
Retrieve information about how the transaction was initiated EXTRACT ATTACH yes yes no
EXTRACT PROCESS no yes yes
Send data SEND yes yes yes
Send further LUTYPE6.1 FMHs SEND ATTACHID yes yes no
Send further LUTYPE6.1 FMHs SEND FMH yes yes no
Receive LUTYPE6.1 FMHs EXTRACT ATTACH yes yes no
Receive data RECEIVE yes yes yes
Send and receive data CONVERSE yes yes yes
Program error ISSUE ERROR no yes yes
Abend conversation ISSUE ABEND no yes yes
Request change of direction ISSUE SIGNAL yes yes yes
Await SIGNAL condition WAIT SIGNAL yes no no
Synchronize Level 0 no yes(8) yes
Synchronize Level 1
SEND CONFIRM
ISSUE CONFIRMATION
 
no
no
 
yes(8)
yes
 
yes
yes
Synchronize Level 2
SEND CONFIRM
ISSUE CONFIRMATION
SYNCPOINT
SYNCPOINT ROLLBACK
 
no
no
yes
no
 
yes(8)
yes
yes
yes
 
yes
yes
yes
yes
Notes on migration of LUTYPE6.1 programs:
  1. The CICS transaction identifier is included in the first four bytes of the data. No attach FMH generated.
  2. An LUTYPE6.1 attach FMH is generated.
  3. An LUTYPE6.1 FMH provided by the application program is sent.
  4. An APPC attach FMH is generated, but with no TPN (TPNL=0). The CICS transaction identifier is included in the first four bytes of the data.
  5. An APPC attach FMH and an LUTYPE6.1 attach FMH are generated.
  6. An APPC attach FMH and an LUTYPE6.1 FMH (provided by the application program) are sent.
  7. An APPC attach FMH is generated.
  8. Sync levels 0 and 1 can be used if CONNECT PROCESS has been used to define the sync level in operation. If CONNECT PROCESS has not been used, sync level 2 is assumed.
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