Example 6. IMS-to-IMS message switch routing with MFS

In the following figure, terminal T enters a transaction to be processed in the backend IMS subsystem.

Message flows from terminal to MID1 and MOD2 on IMS A, then to MID3 in Control Region of IMS B, then to TRANX in MPP of IMS B, then to MID4 and MOD5 back on IMS A, and then to terminal again.

The reply from the back-end subsystem is to be routed back to the original terminal that entered the transaction (T).

Terminal T enters its input from a formatted screen. The terminal only needs to enter data.
After editing by MID1, the message is placed on the message queues and looks like this:
```
LTISC1 | TRANX | Data...
```
The values LTISC1 and TRANX were appended to the data by MFS.
MOD2, to be used for editing the data stream that is sent to IMSB, is chained from MID1, and is chained to another MID (MID4) within IMSA. The data stream to be sent to IMSB looks like this:
```
FMH: DPN=SCHEDULER
```
```
FMH: DPN=MID3,PRN=,RDPN=MID4,RPRN=T
```
```
TRANX | Data...
```
1. DPN=MID3 can be supplied by MOD2 or from a literal in the DOF associated with MOD2.
2. PRN= is not needed, because TRANX is already in the data stream. It could have been supplied from MOD2 or its associated DOF.
3. RDPN=MID4 is specified, because MID4 is chained to MOD2.
4. RPRN=T is again automatically inserted by IMSA as a default function of message switching and not overridden by MFS.
5. LTISC1 again has been stripped from the output message by the MFS MOD.
Upon receipt of the data stream from IMSA, IMSB edits the data using MID3, because the DPN in the FMH specified MID3.
The application receives and processes the following:
```
TRANX | Data...
```
Output from the application program is sent by IMSB to IMSA in the following format:
```
FMH: DPN=SCHEDULER
```
```
FMH: DPN=MID4,PRN=T,RDPN=,RPRN= | Data...
```
DPN=MID4 and PRN=T are automatically wrapped by IMS from the RDPN and RPRN values in the original FMH.
On receipt of this data stream, MID4 in IMSA edits the input and places the message on the queues for final output to terminal T in the following format:
```
Data...
```
Because PRN=T is supplied, IMS uses it as the destination. Because MFS is also used to format the input reply, the PRN is not appended to the data.
Because MOD5 is chained to MID4, MOD5 is used to format the output to terminal T.

Several observations can be made about this example:

MID3 in IMSB is not chained to a MOD. Therefore, the I/O PCB that the application program in IMSB sees does not contain a MODname to be used for output. If MID3 should have a chained MOD, the application ISRT call should have a blank MOD name to negate MFS editing on output.
The application in IMSB has not changed the MOD name for output. If it does, additional MFS format design is required.
The MPP in IMSB can be an already-existing program that also handles transactions from terminals connected to IMSB. The use of MFS can make the use of an ISC session transparent to the application.
The original input terminal is not held in response mode.