Lantronix MPS100 Guide d'installation télécharger pdf (Page 23)

Concepts PostScript

2-9

2.7.2 Access Lists

Since NetWare networks can have hundreds of fileservers, the network needs a way to reduce the number

of Server queries, both to reduce network traffic and to prevent long delays in servicing active queues. By

using access lists (created with the Set/Define Protocols NetWare Access command on page 12-31) you

can control which file servers the Server will and won’t poll for print jobs.

The file servers have no control over the Server access lists, so they will never know if a misconfiguration

of the access list prevents them from spooling print jobs to the Server.

2.8 PostScript

Many printers (including all LaserWriters and other AppleTalk compatible laser printers) use a printing

language called PostScript. Unlike other printer protocols, which typically accept ASCII characters and

print them verbatim, PostScript is also a programming language. Shapes and fonts can be defined as

routines and re-used on successive pages, multiple fonts and copies can be printed, and text and diagrams

can be rotated and shifted on pages.

PostScript is also an interactive language, where the printing host can query the printer for its knowledge

about fonts and software versions. If the host expects to receive data from the printer (as is the case for all

AppleTalk printing), the printer must support Bitronics mode and be connected to a bidirectional port such

as one on the Server. PostScript printing from UNIX, LAT, and NetWare hosts, where bidirectional data

flow is not a requirement, can generally use any parallel port.

PostScript is a verbose language; it is recommended that the printer and Server use a baud rate of at least

9600 to communicate over serial lines. A baud rate of 38400 or better is strongly recommended for high-

output duty; see the printer’s documentation for information on changing the serial speed. Also, many

PostScript jobs contain 8-bit characters. The Server is configured for 8-bit characters, but if the printer is

not (the default on many laser printers is 7-bit), some characters will be printed incorrectly. See your

printer’s documentation for details on how to change the character size setting.

Due to the interactive nature of PostScript, it is possible for the printer and host to get out of synch in their

communication. Since the printer “interprets” the entire PostScript job and then prints the pages, it is

possible for the Server to complete the transfer and accept a new job while the printer is still digesting the

last job. For this reason, an end-of-job character (ASCII 0x4 or Ctrl-D) is used to end all PostScript jobs.

Typically the host will send one at the end of the job and the printer will reply with one when it is done

processing the job. For information on end-of-job characters, see Set/Define Service EOJ command on

page 12-55.

The Server will force a Ctrl-D character when PostScript is enabled on the appropriate service and wait for

one in return. Therefore, enabling PostScript is strongly recommended for all PostScript printer

applications. It guarantees that the printer is ready to accept new data when the job actually starts. Job loss

and printer hangs are the usual result if PostScript is not enabled on the service and the printer cannot keep

up with the job rate. High-speed printers may happen to work if the PostScript attribute is not enabled,

simply because they finish the current job in the time it takes for the Server to accept the next one.

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Lantronix MPS100 Guide d'installation Page 23