Implications of MSC for program coding

For the most part, communicating with a remote terminal or program does not affect how you code your program. MSC handles the message routing between systems.

For example, if you receive an input message from a remote terminal, and you want to reply to that terminal, you issue an ISRT call against the I/O PCB—just as you would reply to a terminal in your system.

In the following two situations, MSC might affect your programming:

When your program needs to know whether an input message is from a remote terminal or a local terminal. For example, if two terminals in separate IMS TM systems had the same logical terminal name, your program's processing might be affected by knowing which system sent the message.
When you want to send a message to an alternate destination in another IMS TM system.

Restriction: If a transaction allocated by an LU 6.2 device is destined to a remote system through MSC links, IMS rejects the transaction with the message TP_NOT_Avail_No_Retry.

Directed routing makes it possible for your program to find out whether an input message is from your system or from a remote system, and to set the destination of an output message for an alternate destination in another IMS TM system. With directed routing, you can send a message to an alternate destination in another IMS TM system, even if that destination is not defined in your system as remote.

Restriction: MSC directed routing does not support a program-to-program switch between conversational transactions.

Related Reading: For more information about LU 6.2 and about MSC directed routing, see IMS Version 15.4 Communications and Connections.