gms@psuvm.bitnet.UUCP (02/05/87)
I received the following information from Skip Grandy at the University
of Pittsburgh Computer Center. His phone number is (412) 624-6355. His
full address is at the end of this posting.
------
Connecting a Xerox 8700 / 9700
Online to a
VAX / VMS Computer Using DDCMP Protocol
On October 20, 1986 the University of Pittsburgh became operational
with an online DDCMP connection between a VAX 8600 computer running
the VMS operating system (4.3) and a Xerox 8700 printing system using
DEC DMR11 interfaces. A DMR11 installed in the PDP11 control computer
in the Xerox 8700 on campus communicates directly with another DMR11
installed in a DEC VAX 8600 at the central computer center located
approximately six miles away.
This accomplishment was the result of a research and development
effort between Computing and Information Systems of the University of
Pittsburgh and Xerox Corporation. Xerox is now considering offering this
as a product. Please read about the following features and show your
interest by sending a letter with comments and/or advising your Xerox
representatives so that it can be factored into the decision by Xerox. If
there is insufficient interest expressed in this approach, Xerox will not
bother to market it as a product.
Design features of this work include:
A) Bidirectional path instead of the unidirectional approach of 3211
printer emulation using the bus and tag interface to the Xerox 8700.
This permits files modified on the Xerox 8700 to be uploaded to the host
VAX computer for backup. The only exception to this is proprietary font
files. Such font files may only be downloaded from the VAX. Our Xerox
8700's do not have the tape drive options installed on them with a
resulting savings in cost. Our need for tape drive service for Xerox
software distribution is handled by the tape drives attached to the VAX
computer.
B) Wide range of bandwidth for remote or local operation.
The DMR11 interface can operate from 2400 bits per second to 1 million
bps. We have routinely debugged this project using Racal-Vadic model
2400PA modems operating synchronously to connect a Xerox 8700 in El
Segundo to the VAX:8600 in Pittsburgh. We have now upgraded the
bandwidth for our production unit on campus from 56 Kbps to to 288:Kbps.
This was conveniently available on our General DataComm Megamux
channel bank and more than sufficient to keep bandwidth from being a
bottleneck to full printer speed.
C) Realtime online feedback of accounting data for each job.
Accounting information is fed back over the bidirectional interface path as
each job is completed. This is in comparison to the other Xerox 8700
options of paper, magnetic tape or the 850 communications link. This
feature has a problem currently as we find it necessary to concatenate
jobs on the VAX in order to avoid the time involved in cycling the Xerox
8700 print engine between an operational and idle state for each of the
small jobs sent. If we did not combine them into bigger jobs, we would
have an unacceptable throughput rate due to the large number of small jobs
which we process. We expect to complete testing software by March 1987
which will achieve this goal of accounting data feedback on a job basis
without slowing down the printer. The Xerox 8700 software will be
concatenating the jobs from the VAX as reports of a larger job within the
Xerox 8700. It will then feed back the accounting data it receives for each
report to the VAX as an individual job accounting item. We will then have
accurate data for jobs which may have been aborted or changed for some
reason by the Xerox 8700 operator instead of the current situation of
processing the print data on the host and estimating how many pages and
images were created.
D) Approach with DMR11 is applicable to all DEC VAX computers.
Even the newest members of the VAX line with VAXBI interfaces offer a
Unibus option to which the DMR11 connects.
E) Not dependent on the DMR11 interface.
The key to this implementation is the DDCMP protocol. For example, while
it has not been tested, we believe that the only one change is necessary to
enable the VAX code to run under MicroVMS on a MicroVAX. This would be
to change the pointer to the device driver which has the DDCMP support on
the MicroVAX. The most likely device for a MicroVAX is the DMV11
interface. Likewise on the mainframe VAX computers, if a more desirable
DDCMP product became available, only changing the pointer to the new
driver routines would be required to implement it. To support a device
other than the DMR11 on the Xerox 8700/9700, only a new software device
driver would have to be implemented.
F) Automatic setup for all types of output.
The Xerox 8700 operator does not have to use the console to change setups
for the different types of output. This is all handled automatically with
the insertion of DJDEs by the VAX print symbiont for the different job
characteristics. This avoids manual intervention and thus improves
throughput.
G) Reasonable hardware costs.
While the current list price for a DMR11-M board set is $ 4,975 and $ 290
for any model of the cabinet connector kit from DEC, they are currently
available from third parties for less than half of this. The DMR11
supports five methods for communications: RS232, RS422, RS423, V.35,
and an Integral Modem. Installation of a particular cabinet kit determines
which method is to be used. From DEC, a MicroVAX DMV11-M
(RS232/422/423) is $ 2,125 and DMV11-N (V.35/Integral Modem) is
$ 1,800. The DMV11 cabinet kits are $ 270 (RS232/422/423), $ 740
(V.35) and $ 440 (Integral Modem).
H) Security from users submitting their own DJDE entries.
The VAX print symbiont does not permit unauthorized use of DJDEs from
users. This is accomplished by the VAX print symbiont processing the user
data and preventing it from being in the form which the Xerox 8700 is
recognizing as a DJDE record. The Scribe output which needs to pass DJDEs
is identified and reformatted to permit it to do its page layout.
I) Simultaneous connection to both a VAX and IBM mainframe.
The DMR11 installation in a Xerox 8700 was put in available Unibus slots
of the PDP11 control computer and did not displace any other interface. It
is possible to have the Xerox printer connected to both a DEC VAX computer
and an IBM mainframe in either a local or remote type of configuration.
The software in the Xerox 8700 does not permit it to be active with both
interfaces simultaneously but by simply using the Xerox 8700 console, one
interface may be shut down and the other interface activated. This would
occur with no changing of cables. One use of this would be to permit two
Xerox printers to be crossconnected between a VAX and IBM mainframe to
permit load sharing and a backup capability to exist for an out of service
printer. Likewise 850/860 CWP equipment may also be cabled in at the
same time but may not receive data at the same time as the HIP or Bus & Tag
interface.
J) Remote printers can backup each other.
Some businesses have multiple Xerox 8700/9700's in different locations,
even including different cities. By obtaining a leased or dialup service at
56 Kbps, it becomes easy to configure a situation which would permit
such machines to serve as backups for each other. The data rate of
56 Kbps should be quite sufficient to drive a Xerox 8700 at full speed
with text data. While 56Kbps would not be sufficient to operate a Xerox
9700 at full speed, it may well be adequate for a backup mode.
K) Able to print any size output.
Like the line printer (3211) interfaces, any length output may be printed
using this DDCMP software. This is not a feature of the
Interpress/Ethernet/CWP interface. The software handling Interpress
cannot begin the printing process until the job has been completely
received onto the Xerox spooling disk. The DDCMP approach passes data for
printing a job while it is also receiving additional data for the same job
and therefore does not restrict the length of any output file.
L) Support for many types of output.
Support in this VAX print symbiont exists for:
Computer output with forms overlay
Standard Scribe output
Scribe output with merged graphics *
Plot output from DISSPLA/TEL-A-GRAF *
* This feature requires another University of Pittsburgh proprietary VAX
program which rasterizes Zeta GML plotter code.
M) Software consumes small amount of resources.
The VAX print symbiont code requires fifty six blocks (512 bytes per
block) of disk space. CPU resource requirements are kept small by using
the DMR11 which is a DMA device. The CPU utilization of the print
symbiont on a DEC VAX 8600 is .001 CPU seconds per 512 byte sector of
output.
N) Limit of 128 possible characteristics.
In the Environmental Characteristics section of the reference manual it
notes that there is a limit of 128 possible characteristics for the print
jobs. This is a DEC VAX/VMS limit which is noted in the DEC DCL manual
under DEFINE/CHARACTERISTIC. We did not implement forms control with
the FORM option of VMS because to use it would require manual
intervention. An operator would be required to control the print queue in
order to switch from one form type to another. Instead, this
implementation permits different forms types on the Xerox 8700 to be
automatically selected by DJDEs issued by the print symbiont.
O) Future possibilities.
We are looking at TEX and XICS as other possible formats which can be
handled by the print symbiont. This would permit them to pass their DJDEs
to the 8700/9700. It would also be possible to have a generic format
designed which would permit any user to send their own DJDEs.
The University of Pittsburgh has two Xerox 8700 printing systems. The
Administrative Xerox 8700 is currently connected directly to the NAS
8053 via a bus and tag channel extender. We are currently looking at
products which will provide a high bandwidth communication path between
our NAS 8053 IBM compatible mainframe and our now upgraded VAX 8650
VMS 4.5 mainframes. This will then permit us to direct connect our
Administrative Xerox 8700 as well as the Academic Xerox 8700 to our VAX
computers. Output for Administrative and Academic users may then be
routed to the printer most appropriate to speed delivery to the user.
For further information contact:
Allen Grandey
University of Pittsburgh
Computing and Information Systems
600 Epsilon Drive
Pittsburgh, Pa. 15238-2887
(412) 624-6355 ASG 1-7-87
Bitnet ASG@PITTVMS