A P   S P E C I A L   C O M P U T E R   P R O J E C T S   G R O U P

			S T A F F  M E M O


	Using the High Speed printer from RSX servers
	---------------------------------------------


Printer usage on the RSX server systems should now be simpler.
There is one high speed printer on the Distributed Market System 
network. This printer, a CI-600, is connected to the MicroVAX A 
system. None of the other system have a dedicated printer.

New software on RSX systems now makes this one printer appear as if 
it is connected directly to each system. The standard RSX PRInt 
command will function as described in the DEC documentation.

The old method of copying a file to RPRINT::$PRINTER: across the 
network will still work.

 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Details:

All RSX systems now have a new device, VP:, that looks to the system 
like a regular line printer. VP: is set spooled and fed by the queue 
manager.

VP: is actually a virtual device connected to a special DECnet task. 
Each buffer sent to VP: is tranfered across the network to the 
system that has the physical printer attached to it. In practice, 
this is MICVXA, but could be any other VAX on the net.

By intercepting print jobs at the device level, all the standard 
features offered by the RSX print system are maintained including 
flag pages, multiple copies of file and special forms capability.

Actual printing will not start until the entire print job has been 
transfered across the network. For very long printouts, this means 
the printer may not start for some time.

 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Implementation, restrictions:

The VP: device requires the VPVDV task. This task is privileged, and 
lives in the network uic, [5,54].

VPVDV is installed by name and started in the startup command file. 
VPVDV's owning TI: should be CO:, therefore the task should is started 
using the RUN command with a 1 second delay.

The VP: driver passes all IO packets to VPVDV. VPVDV transmits the 
data buffer specified in a QIO write to a task on the print server 
system.

QIO attach and detach packets are also passed to VPVDV, and are
particularly important. The VP: device assumes that a task will
attach to it before starting a print run, and detach when it
completes. The attach request is used to trigger a DECnet connect to
the print server system. 

On the VAX system that is acting as the print server, the connect 
starts a DCL command procedure that copies all network data sent to 
it into a temporary file. When the VPVDV task issues a disconnect, 
the file is closed and queued for printing on the VAX system. The 
VAX print command requests printing with no header or trailer pages, 
and deletes the temp file after printing.

On the RSX side, when the VP: device is spooled, it is set as a 
shared, spooled device. This forces the LPP despooler task to 
attach and detach the device on each print job.

More than one RSX system can be sending print jobs to the VAX print 
server, each connect request to the VAX starts a new copy of the DCL 
command procedure.