When to use the data stream interface

You can use the data stream interface for the following types of applications:

With passthrough; that is where the application passes data through, usually to the user's terminal, without doing anything to it.
With SLU P.
Where the formatted interface does not provide the detailed function that you need.
For handling non-3270 LU2 devices.
With non-response mode IMS transactions.

The 3270 data stream interface is especially useful when creating FEPI applications that require little or no manipulation of the inbound (screen) data, because it is already in a form suitable for sending to a real terminal. If interpretation or reformatting of the inbound data is required, however, it can be significantly more difficult to operate on a 3270 data stream.

An example of an application suited to the 3270 data stream interface is a passthrough program, as illustrated by the FEPI sample program: 3270 data stream passthrough . Such programs can also be used to determine the flows and screen layouts of back-end systems when you are developing FEPI applications that, for example, drive signon or menu selection sequences and manipulate screens or dialogs.

You must be fully conversant with the data stream and data stream protocols as detailed in the books in the following list, and with how the back-end system uses them:

The application program is entirely responsible for the integrity of the data stream that uses this interface. FEPI performs no checking or interpretation on the data stream that is sent to or received from the back-end system, and makes no attempt to manipulate data into RU sizes that the sender or receiver can handle; the application program must be prepared to handle whatever data is presented to it. For example, with SLU2 mode, it must be prepared to handle READ commands, and WRITE STRUCTURED FIELD commands, in addition to the normal WRITE commands.