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 13 Communications and Connections.