Example 5. IMS-terminal-to-other-terminal message switch routing

The following figure is similar to Example 4; however, the back-end subsystem is CICS® or a user-written subsystem.

Figure 1. ISC example for IMS-terminal-to-other-terminal message switch routing
Begin figure description: Message flows from Terminal 1 to Basic Edit and Message Switch on IMS A, then to ISCE on a non-IMS subsystem, and then returns to Terminal 2. End description.

The description of the activities taking place in IMS in this example parallels the description in Example 1 exactly. The other subsystem is of interest is described.

  1. Assume the other subsystem is CICS. Remember from Example 1 that the data stream sent from IMS looks like this: 
    FMH: DPN=ISCE,PRN=,RDPN=,RPRN=T | Data...
  2. As in Example 3, CICS must have a transaction code defined as ISCE.

    The data is formatted in the way in which ISCE expects to receive it. The IMS terminal operator who is entering the transaction should understand what that format is to be. CICS, upon receiving the data stream, must invoke a transaction named ISCE, specifically written for the ISC environment. This transaction uses the data in the input FMH and obtains the input data through the RETRIEVE interface. Because the PRN field in the input FMH is not initialized by IMSA to be equal to T2, the CICS application must initiate a message switch to terminal T2 from the transient data queue or start a new transaction naming T2 as the primary resource.

    In this example, the output terminal T2 must be identified in the input data stream. If IMSA had initialized the PRN field in the input FMH to T2, CICS would have attached the transaction ISCE with T2 as the primary resource, and a SEND to terminal T2 could have been made directly.

  3. In order for IMSA to set the PRN field, MFS would be required.