PSF direct or distributed print function (DPF)

Printers can be remotely attached with PSF direct or a distributed print function (DPF).

PSF direct

In a PSF direct configuration, PSF sends the print data set over an SDLC line, local token ring, or remote token ring to PSF direct, which passes the data set to a printer attached to a print server.
Note: PSF direct does not support remote resource caching.
When you are installing and configuring PSF direct, consider these:
  • Data rate capability of the printer
  • Data rate capability of the host attachment
  • Data rate requirements of the print data set
Note: The use of data stream transforms, such as AFP to PCL, can decrease throughput.

DPF

DPF works with Resource Saving either OFF or ON.

In a DPF configuration, PSF sends the print data set over an SDLC line, local token ring, or remote token ring to DPF, to be spooled and later printed. DPF requires only one print server, which spools the print data sets in one stage and sends them to be printed in another stage.

The maximum data rates in DPF can be lower than data rates with PSF direct, depending on attachment speeds.

Size of the VTAM request unit (RU)

A VTAM® request unit (RU) contains system data information for a printer. An increase in VTAM RU size might increase printing rate because processing larger (and therefore fewer) RUs contributes to higher efficiency.

However, the maximum size of the RU is limited and dependent upon the limitations of hardware and software. For example, the RU size is limited by the communications controller or by the maximum buffer size that is allowed by the printer, whichever is smaller. Generally, use the largest RU size suitable for the printer or attachment that is used.

VTAM PSNDPAC and DELAY parameters

VTAM includes a coat-tailing algorithm that is designed to minimize the number of buffers VTAM processes. In intermediate-speed and high-speed communication configurations, this algorithm can affect the performance both of communication-attached printers and of DPF or PSF direct.
  • In intermediate-speed communication configurations, you can reduce or eliminate coat-tailing delays by specifying a large PSNDPAC pacing value in your VTAM logon-mode table entry.
  • In high-speed communication configurations, you must eliminate coat-tailing delays to achieve full use of high-speed communication links. VTAM provides a DELAY parameter for this purpose; specify DELAY=0.
For more information about coat-tailing, see z/OS Communications Server: SNA Customization.

NCP MAXOUT value

MAXOUT (maximum output) is an operand in the physical unit (PU) macro instruction for the Network Control Program (NCP). The value that is specified for MAXOUT defines the number of units of data that the host system can send to the PU before the PU must respond. You must specify a value 3 - 7. A value less than the maximum supported by the PU can cause delays in the communication line, and thus degrade performance. For more information, see NCP: System Support for your system.