Intercommunication rules and restrictions checklist

This appendix provides a checklist of the rules and restrictions that apply to intersystem communication and multiregion operation.

Most of these rules and restrictions also appear in the body of the book. The rules apply to:

Transaction routing

There are a number of rules and restrictions that apply to transaction routing, to review the entire checklist see Transaction routing.

Dynamic routing of DPL requests

For a distributed program link request to be eligible for dynamic routing, the remote program must either be defined to the local system as DYNAMIC, or not be defined to the local system. Daisy-chaining of dynamically-routed DPL requests is not supported, see Daisy-chaining of DPL requests.

Automatic transaction initiation

  • A terminal-associated transaction that is initiated by the transient data trigger level facility must reside on the same system as the transient data queue that causes its initiation. This restriction applies to both macro-level and command-level application programs.
  • There are restrictions on the dynamic routing of transactions initiated by EXEC CICS® START commands, see the list of conditions in Transaction routing.

Basic mapping support

  • BMS support must reside on each system that owns a terminal through which paging commands can be entered.
  • A BMS ROUTE request cannot be used to send a message to a selected remote operator or operator class unless the terminal at which the message is to be delivered is specified in the route list.

Acquiring LUTYPE6.1 sessions

  • If an application tries to acquire an LUTYPE6.1 connection and the remote system is unavailable, the connection is placed out of service.
  • If the remote system is a CICS region that uses AUTOCONNECT, the connection is placed back in service when the initialization of the remote system is complete
  • Otherwise, you must manually place the connection back in service.

Function shipping

You can use CICS function shipping to write CICS application programs without regard to the location of the requested resources. They use file control commands, temporary-storage commands, and other functions in the same way.

Syncpointing

SYNCPOINT ROLLBACK commands are supported by APPC, IPIC, and MRO sessions.

Local and remote names

Local names are translated to remote names according to these rules.

  • Transaction identifiers are translated from local names to remote names when a request to execute a transaction is transmitted from one CICS system to another. However, a transaction identifier specified in an EXEC CICS RETURN command is not translated when it is transmitted from the application-owning region to the terminal-owning region.
  • Terminal identifiers are translated from local names to remote names when a transaction routing request to execute a transaction on a specified terminal is shipped from one CICS system to another. However if an EXEC CICS START command specifying a terminal identification is function shipped from one CICS system to another, the terminal identification is not translated from local name to remote name.

Main terminal transaction

Only locally owned terminals can be queried and modified by the main terminal transaction CEMT. The only terminals visible to this transaction are those owned by the system on which the main terminal transaction is running.

Installation and operations

  • Module DFHIRP must be made LPA-resident; otherwise jobs and console commands may abend on completion.
  • Interregion communication requires subsystem interface (SSI) support.
  • Do not install more than one APPC connection between an LU-LU pair.
  • Do not install an APPC and an LUTYPE6.1 connection at the same time between an LU-LU pair.
  • Do not install more than one MRO connection between the same two CICS regions.
  • Do not install more than one generic EXCI connection on a CICS region.

Customization

  • Communication between node error programs, user exits, and user programs is the responsibility of the user.
  • Transactions that recover input messages for protected tasks after a system crash must run on the same system as the terminal that invoked the protected task.

MRO abend codes

  • An IRC transaction in send state is unable to receive an error reason code if its partner has to abend. It abends itself with code AZI2, which should be interpreted as a general indication that the other side is no longer there. The real reason for the failure can be read from the CSMT destination of the CICS region that first detected the error. For example, a security violation in attaching a back-end transaction is reported as such by the front end only if the initiating command is CONVERSE and not SEND.