IMS use of routing parameters

IMS ISC without the Front-End Switch exit routine does not provide for automatic transaction routing when IMS is the front-end subsystem.

These transactions can be sent as alternate PCB output from a user-written application program within IMS or by using an ISC message switch. In the latter case, the source terminal operator provides the output routing information through an ISC destination LTERM name which is the required first data field on IMS message switches.

Except when the output is formatted by MFS (by using a MOD chained from the input MID associated with the message switch), IMS message routing support for ISC removes the first data field before sending the balance of the message text to the back-end subsystem. When MFS is used to format message switch output, you should use MFS editing to remove the output LTERM name.

Further, ISC message routing support within IMS defaults the RPRN within the output FM header sent with the message to the LTERM name associated with the terminal that was the source of the message switch. For alternate PCB output, the RPRN is set to the I/O PCB name. The RPRN allows IMS to automatically route message replies from the remote subsystem back to the source terminal in the form of a message switch, provided the other subsystem has returned the RPRN parameter as the PRN parameter on the reply. MFS DPM can be used to alter the FM header destination and return routing parameters. When using IMS as a front-end subsystem to route messages to another subsystem or route replies back to the source terminal, MSGDEL=SYSINFO must be specified on the IMS system definition TERMINAL macro statement or an ETO user descriptor associated with both the ISC session and the source terminal.