02. Methods for printing

Method for printing
There are various methods an R/3 Spool System can use to access an operating system spooler.

Local printing

The operating system spooler runs on the same host as the R/3 spool work process.

In Windows NT systems, the spool work process uses operating system calls to pass output to the printer manager using the Windows NT API (access method C).

In UNIX systems, the output request is passed to the operating system spooler using UNIX commands, for example lp or lpr (access method L). The form of the command is specified in the R/3 System profile.

Local printing is the fastest and most reliable way of printing in R/3. Local printing does not mean that the printer is physically attached to the host running the R/3 spool work process. The operating system spooler can print on either a locally or remotely attached printer.

Remote printing

When using remote printing, an R/3 spool work process passes the print-ready output stream to the operating system spooler on a different host. This data transfer requires moving the output stream across a network link. The operating system spooler can then print on either a locally or remotely attached printer.

Some printers haver their own operating system spooler. They can be directly attached to a network through a network card interface. They are called network printers, and can also receive output from R/3 (access method U).

In UNIX systems, the output stream is sent to a line printer demon lpd (access method U).

In Windows systems and other systems without an lpd, SAP provides the program saplpd, which receives the output stream and transfers it to the operating system spooler (access method S for a proprietary SAP protocol or U for the UNIX Berkeley protocol).

For performance reasons, the remote access methods are only suitable for LAN environments and require reliable communication partners.

Front end printing

Front end printing allows R/3 users to send output to printers that are defined on their local front end PCs (access method F). The spool administrator does not need to define these printers as output devices in R/3.

In Windows systems, the output is sent to program saplpd on the frontend PC. If saplpd is not running, it is started automatically.

In other systems (UNIX, Macintosh, ...), the output is passed to the operating system spooler.

As of Release 4.6A, all spool processing takes place in a spool work process. The spool work process waits until the output has been sent to the frontend before it continues to process other requests. Therefore, performance problems can occur when frontend printing is used.

You can set an upper limit to the number of spool work processes used for frontend printing using parameter rdisp/wp_no_spo_Fro_max. The default value of the parameter is 1.

Front end printing only works as long as there is an active connection to the frontend PC. Therefore, frontend printing cannot be used in background processing.

For more information on frontend printing and release dependencies, see SAP Collective Note 114426.