[printing-discuss] Bi-directional communication instantiated as a Stream Manager....

[Glen Petrie]

Hello All,

There have been several discussions on bi-directional communication.   This
is the communication between the printing processes and the printer is
mostly for status information and is shown differently on the various
architecture diagrams.  In one case, it is called the =93printer communicat=
ion
daemon=94 (via the =93translation service=94) and on the other architecture
diagram the bi-directional communication is by the =93Bi-Di UI interface AP=
I=94
but appears to be independent of the printer-driver.   I would like suggest
the following diagram as a possible solution

(diagram was made using Courier New at 10 pt)


                 -----------------------------         -------------
                 |                           | <-----> |dir service|
                 |    Print Manager          |         -------------
                 |                           |         -------------
                 |                           | <-----> |  render   |
                 -----------------------------         -------------
                   ^           ^          ^
                   |           |          |
                   |           |          v
                   |           |     --------------
                   |           |     |  Spooler   |
                   |           |     --------------
                   |           |          ^
                   |           |          |
                   |           v          v
                   |          --------------
                   |          |Printer Drv |
                   |          --------------
                   |                ^
                   |                |
                   v                v
                 -------------------------------------------------
                 |     Stream Manager                            |
                 -------------------------------------------------
                   ^        ^        ^        |        |        ^
                   |        |        |        |        |        |
                   v        v        v        v        v        v
                 serial    usb     parallel  file  memory   what-ever

(there are other architecture elements missing but not key to this note.)

This diagram illustrates that communication between the output portals
(serial, usb, parallel, a file, memory or what-ever (future)) is done via a
Stream Manager or more specifically a Stream Manager API.   In this case the
Print Manager and/or Printer Driver uses the single API to communication
with a variety of output portals -- always in the same way.   Portals can be
interrogated for bi-directional capabilities and, where available, the
status information can be read.   Since, requesting status information is
(almost always) vendors specific (ie. the calling sequences for specific
information), all communication  (print data and status) between the print
device (output portal) should go through the printer driver.  The Print
Manager may request status by directly making request to the printer driver
while possibly sending data via a spooler.   The Print Manager may make
inquires of the stream manager to determine possible portals and/or status
of individual portals.

Rgds,
Glen W. Petrie
Manager, Software Printing Solutions
Epson Imaging Technology Center
150 River Oaks Parkway, Suite 200
San Jose, CA, 95134
Voice: 408.576.4131  Fax: 408.474.0511

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