Specifying how NetSpool determines end-of-file

To guarantee that data that belongs together actually gets printed in the correct order, NetSpool writes data that belongs together to a single output data set on the JES spool. For printing in the SNA network, the concept of a data set is not needed because an application starting a session with a printer gains exclusive control of that printer for the duration of the session. In contrast, when printing in a JES environment, the sending application is not guaranteed exclusive control of the printer. Between two successive data sets from one application, data sets from other applications might print. If the first attempt to print a data set fails, and a later retry succeeds, two successive data sets from the same application could even be printed in reverse order.

To create an output data set, NetSpool must determine where one data set should end and the next one should begin. You specify the rules that NetSpool uses to make this determination. You can specify different rules for different combinations of VTAM® primary logical unit (PLU) names and LU types. The PLU name identifies the VTAM application that sends data to NetSpool.

The rules generally use information found in the input data stream to determine when to end the current output data set. VTAM request unit (RU) chaining information can be used, a string in the input data stream can be used, or even a timer can be used. Work with the application programmers in your installation to determine the appropriate end-of-file rules for each printer definition.