Considerations for IMS

If your CICS® installation is to use CICS-to-IMS™ intersystem communication, you must ensure that the CICS and the IMS installations are fully compatible.

The following sections are intended to help you communicate effectively with the person responsible for installing the IMS system. They may also be helpful if you have that responsibility. You should also refer to Defining links to remote systems, especially the section on defining compatible CICS and IMS nodes. For full details of IMS installation, refer to the IMS/ESA Installation Guide.

ACF/VTAM definition for IMS

When the IMS system is defined to VTAM®, the following operands should be included on the VTAM APPL statement:

AUTH=(ACQ,VPACE)
ACQ is required to allow IMS to acquire LU type 6 sessions. VPACE is required to allow pacing of the intersystem flows.
VPACING=number
This operand specifies the maximum number of normal-flow requests that another logical unit can send on an intersystem session before waiting to receive a pacing response. An initial value of 5 is suggested.
EAS=number
The number of network addressable units must include the total number of parallel sessions for this IMS system.
PARSESS=YES
This operand specifies LU type 6 parallel session support.

For further information about the VTAM APPL statement, see the OS/390 eNetwork Communications Server: SNA Resource Definition Reference manual.

ACF/VTAM LOGMODE table entries for IMS

IMS allows the user to specify some BIND parameters in a VTAM logmode table entry. The CICS logmode table entry must match that of the IMS system. IMS uses (in order of priority) the mode table entry specified in:

  1. The MODETBL parameter of the TERMINAL macro
  2. The mode table entry specified in CINIT
  3. The DLOGMODE parameter in the VTAMLST APPL statement or the MODE parameter in the IMS /OPNDST command
  4. The ACF/VTAM defaults.

Figure 31 shows a typical IMS logmode table entry:

Figure 31. A typical IMS logmode table entry
LU6NEGPS  MODEENT LOGMODE=LU6NEGPS,  NEGOTIABLE BIND
            PSNDPAC=X'01',           PRIMARY SEND PACING COUNT
            SRCVPAC=X'01',           SECONDARY RECEIVE PACING COUNT
            SSNDPAC=X'01',           SECONDARY SEND PACING COUNT
            TYPE=0,                  NEGOTIABLE
            FMPROF=X'12',            FM PROFILE 18
            TSPROF=X'04',            TS PROFILE 4
            PRIPROT=X'B1',           PRIMARY PROTOCOLS
            SECPROT=X'B1',           SECONDARY PROTOCOLS
            COMPROT=X'70A0',         COMMON PROTOCOLS
            RUSIZES=X'8585',         RU SIZES 256
            PSERVIC=X'060038000000380000000000'  SYSMSG/Q MODEL
          MODEEND

IMS system definition for intersystem communication

This section summarizes the IMS ISC-related macros and parameters that are used in IMS system definition. You should also refer to Defining compatible CICS and IMS nodes. For full details of IMS installation, refer to the installation guide for the IMS product.

The COMM macro

APPLID=name
Specifies the applid of the IMS system. For an IMS system generated without XRF support, this is usually the name that you should specify on the NETNAME option of DEFINE CONNECTION when you define the IMS system to CICS.

However, bear the following in mind:

For an explanation of how IMS system names are specified, see topic System names.

RECANY=(number,size)
Specifies the number and size of the IMS buffers that are used for VTAM "receive any" commands. For ISC sessions, the buffer size has a 22-byte overhead. It must therefore be at least 22 bytes larger than the CICS buffer size specified in the SENDSIZE option of DEFINE SESSIONS.

This size applies to all other ACF/VTAM terminals attached to the IMS system, and must be large enough for input from any terminal in the IMS network.

EDTNAME=name
Specifies an alias for ISCEDT in the IMS system. For CICS-to-IMS ISC, an alias name must not be longer than four characters.

The TYPE macro

UNITYPE=LUTYPE6
Must be specified for ISC.

Parameters of the TERMINAL macro can also be specified in the TYPE macro if they are common to all the terminals defined for this type.

The TERMINAL macro

The TERMINAL macro identifies the remote CICS system to IMS. It therefore serves the equivalent purpose to DEFINE CONNECTION in CICS.

NAME=name
Identifies the CICS node to IMS. It must be the same as the applid of the CICS system (the generic applid for XRF systems).
OUTBUF=number
Specifies the size of the IMS output buffer. It must be equal to or greater than 256, and should include the size of any function management headers sent with the data. It must not be greater than the value specified in the RECEIVESIZE option of the DEFINE SESSIONS commands for the intersystem sessions.
SEGSIZE=number
Specifies the size of the work area that IMS uses for deblocking incoming messages. We recommend that you use the size of the longest chain that CICS may send. However, if IMS record mode (VLVB) is used exclusively, you could specify the largest record (RU) size.
MODETBL=name
Specifies the name of the VTAM mode table entry to be used. You must omit this parameter if the CICS system resides in a different SNA domain.
OPTIONS=[NOLTWA|LTWA]
Specifies whether Log Tape Write Ahead (LTWA) is required. For LTWA, IMS logs session restart information for all active parallel sessions before sending a syncpoint request. LTWA is recommended for integrity reasons, but it can adversely affect performance. NOLTWA is the default.
OPTIONS=[SYNCSESS|FORCSESS]
Specifies the message resynchronization requirement following an abnormal session termination. SYNCSESS is the default. It requires both the incoming and the outgoing sequence numbers to match (or CICS to be cold-started) to allow the session to be restarted. FORCSESS allows the session to be restarted even if a mismatch occurs. SYNCSESS is recommended.
OPTIONS=[TRANSRESP|NORESP|FORCRESP]
Specifies the required response mode.
TRANSRESP
Specifies that the response mode is determined on a transaction-by-transaction basis. This is the default.
NORESP
Specifies that response-mode transactions are not allowed. In CICS terms, this means that a CICS application cannot initiate an IMS transaction by using a SEND command, but only with a START command.
FORCRESP
Forces response mode for all transactions. In CICS terms, this means that a CICS application cannot initiate an IMS transaction by using a START command, but only by means of a SEND command.

TRANSRESP is recommended.

OPTIONS=[OPNDST|NOPNDST]
Specifies whether sessions can be established from this IMS system. OPNDST is recommended.
{COMPT1|COMPT2|COMPT3|COMPT4}={SINGLEn|MULTn}
Specifies the IMS components for the IMS ISC node. Up to four components can be defined for each node. The input and output components to be used for each session are then selected by the ICOMPT and COMPT parameters of the SUBPOOL macro.

The following types of component can be defined:

SINGLE1
Used by IMS for asynchronous output. One output message is sent for each SNA bracket. The message may or may not begin the bracket, but it always ends the bracket.
SINGLE2
Each message is sent with the SNA change-direction indicator (CD).
MULT1
All asynchronous messages for a given LTERM are sent before the bracket is ended. The end bracket (EB) occurs after the last message for the LTERM is acknowledged and dequeued.
MULT2
The same as MULT1, but CD is sent instead of EB.
SESSION=number
Specifies the number of parallel sessions for the link. Each session is represented by an IMS SUBPOOL macro and by a CICS DEFINE SESSIONS command.
EDIT=[{NO|YES}][,{NO|YES}]
Specifies whether user-supplied physical output and input edit routines are to be used.

The VTAMPOOL macro

The SUBPOOL macro heads the list of SUBPOOL macros that define the individual sessions to the remote system.

The SUBPOOL macro

A SUBPOOL macro is required for each session to the remote system.

NAME=subpool-name
Specifies the IMS name for this session. A CICS-to-IMS session is identified by a "session-qualifier pair" formed from the CICS name for the session and the IMS subpool name.

The CICS name for the session is specified in the SESSNAME option of the DEFINE SESSIONS command for the session.

The IMS subpool name is specified to CICS in the NETNAMEQ option of the DEFINE SESSIONS command.

The NAME macro

The NAME macro defines the logical terminal names associated with the subpool. Multiple LTERMs can be defined per subpool.

COMPT={1|2|3|4}
Specifies the output component associated with this session. The component specified determines the protocol that IMS ISC uses to process messages. An output component defined as SINGLE1 is strongly recommended.
ICOMPT={1|2|3|4}
Specifies the input component associated with this session. When IMS receives a message, it determines the input source terminal by finding the NAME macro that has the matching input component number. A COMPT1 input component must be defined for each session that CICS uses to send START commands.
EDIT=[{NO|YES}][,{ULC|UC}]
The first parameter specifies whether the user-supplied logical terminal edit routine (DFSCNTEO) is to be used.

The second parameter specifies whether the output is to be translated to uppercase (UC) or not (ULC) before transmission.

Related concepts
Installation considerations for multiregion operation
Related tasks
ACF/VTAM definition for CICS
Defining APPC links
Related reference
Modules required for ISC
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