Network Working Group M. A. Padlipsky
Request for Comments: 282 Project MAC
NIC: 8164 December 8, 1971
GRAPHICS MEETING REPORT
The second Network Graphics Group Meeting was convened at the
Stanford Artificial Intelligence Lab at 6:00p.m. Sunday, November
21st. (Attendees are listed in the Appendix.) Jim Michener served
as chairman, and I either volunteered or was volunteered to serve as
recording secretary, with Karl Kelly's assistance in keeping notes.
An agenda was agreed upon for the meeting, covering three major
topics: 1) reports on the eXPeriments which had been set up at the
July meeting, 2) prepared talks by attendees who had general points
to raise about Network Graphics, and 3) specification of a "first-
pass" graphics protocol. Before the reports were given, some general
discussion was held on two important topics: the "context" problem
(just how, in the Network sense, are graphics connections
established, and who is supposed to do what for whom), and what might
be called the "console types" problem (should there be a separate
protocol for inherently static storage tube type devices and one for
inherently interactive refresh type devices which have their own
processors, or can we come up with some sort of continuous -- or
layered -- single protocol which covers both). Both points were
noted as being necessary to keep in mind for the protocol
specification phase of the meeting, an apparent consensus emerged
that a single protocol would be preferable, and the reports on
experiments were turned to.
REPORTS ON EXPERIMENTS
RAND - UCSB
Eric Harslem of RAND and Ron Stoughton of UCSB reported on their
experiment, which entailed use of the UCSB On-Line System (OLS) from
RAND Videographics terminals. As demonstrated by a videotape which
was shown, the experiment was successful. An RFCdescribing the
simple protocol they used is forthcoming. As noted in their
discussion and in the RFC, the experimental protocol is not being
proposed as a Network standard. In addition to using OLS from RAND,
a subsidiary experiment tested the sensitivity of the hook-up to
variations in the size of the allocations (in the Host-to-Host
Protocol sense) given at the RAND end. It seemed clear from the
videotape of the same pictures being drawn at various allocation
levels that larger allocations allow for noticeably smoother
"drawing" at maximum allocation, the picture essentially appeared all
at once, whereas at minimum allocation, NCP-NCP overhead was
sufficiently large that the picture appeared a portion at a time.
SDC - DMCG
An experiment intended to input tablet data collected at MIT Project
MAC's Dynamic Modeling/Computer Graphics Group's PDP-10 to a
character recognizer package at SDC was reported on by Jean Saylor of
SDC and Jim Michener of DMCG. Problems ranging from
hardware/software difficulties at both ends (and in the middle) to
time zone-induced system availability conflicts retarded the
experiment's progress, although some transmission of data has been
achieved.
ILLINOIS MULTICS
Also plagued with problems was the attempt to drive a console at U.
of Ill. from the Multics Graphics System. This experiment was
reported on by Jack Bouknight (Illinois) and Ed Meyer (Multics). An
NCP bug at the Multics end and a machine switch at the Illinois end
combined to prevent the carrying out of the experiment.
DIGRESSION
During his report, Bouknight expressed concern as to whether the
Network as a whole is as yet sufficiently reliable to support
graphics work. As the ensuing discussion focused on the frequent
unavailability of a host other than Multics, I feel that it is within
my province to draw the curtain of anonymity over it without
prejudice. However, I feel that mention of the discussion need not
be suppressed as well, in view of the fact that most of the attendees
shared Jack's concern. The apparent consensus, reached after
considerable conversation, is that the present reliability level of
the Network server hosts is not crippling to graphics work, but can
be quite hampering.
SEX - NIC
Jon Postel (UCLA) and John Melvin (SRI) gave the last experiment
report, on an attempt to make an IMLAC on the SEX system look like a
local NLS console at the Network Information Center. The experiment
has not yet been performed, but UCLA has ordered the necessary
equipment to modify their IMLAC.
PRESENTATIONS
Most of the speakers who gave prepared talks responded favorably to
my plea for abstracts, probably out of kindness, but perhaps out of
fear of (threatened) garbling. Authors' abstracts are in quotation
marks in the following section.
PLASMA PANEL DISPLAY - Dave Liddle
"The Owens - Illinois DS-1 terminal will be available to Network
users who request them through ARPA. The display module is the OI
512X512 line plasma panel; the processor is a 16 bit, 4K machine with
modem; ASCII keyboard, and optional tape cassette. Simple software
(character and vector generators, etc.) will be provided. If orders
can be assembled by 1 January, deliveries will begin this summer."
LANGUAGES FOR GRAPHICS ATTENTION HANDLING - Ira Cotton
"Available languages for programming the processing of operator
inputs to a computer graphic system were organized into functional
classes and briefly surveyed. Some of the problems associated with
providing this facility in a multi-computer graphics system (such as
the Network) were discussed, and a new approach was presented. This
system, implemented by Univac for one of its systems, employs an
interpretively executed command language to direct attention-handling
in the remote graphics controller. The commands of the language were
outlined, and some program fragments illustrated."
"INTERACTIVE" GRAPHICS ISSUES - Ken Pogran
"The purpose of this talk was to raise a number of significant issues
we must face in the development of a Network protocol for
_interactive_ graphics. While the bulk of the work at this second
graphics meeting dealt with a protocol for "static" or "storage-tube"
graphics, it is appropriate that we begin to think about the problems
we will encounter in the development of an interactive graphics
protocol."
"The issues raised included: 1) the nature of graphical interaction,
2) various possible hardware/software configurations which might be
employed, 3) computational capabilities required at the serve and
user host sites, 4) the nature of a graphical data structure suited
to a wide range of applications, and 5) the nature and treatment of
graphic inputs for a generalized interactive graphics system."
PROTOCOL FOR THE OLS EXPERIMENT - Ron Stoughton, Eric Harslem
"A short presentation was given describing a graphics protocol used
to interface the RAND Videographics System to the USCB On-Line
System. A video tape of alive demonstration of the experiment [had
also been] presented. An RFCdescribing the experiment and protocol
in detail will be issued in the near future."
CONNECTION CONSIDERATIONS - Andy Moorer [Abstracted by M.A.P.]
The topic was started succinctly as "how this thing should work." It
was proposed to use the Telnet Protocol for simple graphics (i.e.,
when device dependent codes are being transmitted), with the addition
of Telnet control codes for Enter graphics Mode, Leave Graphics Mode,
and Console Type being necessary. For complex graphics (i.e., when
an intermediate form is being transmitted) it was proposed that an
additional socket pair be employed.
CONNECTION TYPES - Jim Michener [Abstracted by M.A.P]
There are at least three types of graphics devices which may be
connected over the Network: "simple" (ARDS-like), "smart" (IMLAC-
like), and "powerful" (E&S-like). There are three kinds of
processing involved: applications packages (A), graphics packages
(G), and conversion to device-specific codes (C), potentially from an
intermediate form such as the "Network Standard Graphics Stream"
discussed in earlier RFC's. There are also three places where each
kind of processing may be performed: at the graphics device itself,
at the local host (which may not be able to help if it's a TIP), and
at a remote host (OR HOST). This should lead neatly to some sort of
3X3X3 matrix which depicts the sorts of connections we want to
support, but I don't know how to draw it.
The talk leaned heavily on blackboard pictures of specific
connections, but for purposes of this report, I'll try to summarize
the situation in Words. For all simple devices, C must be performed
"elsewhere"; if the simple device is on the Net via a TIP, C
apparently must be performed either at the remote host (RH1) where A
and G are, or at some other remote host (RH2) (which offers, say, the
Data Reconfiguration Service). Further, negotiations for C may have
to be performed by RH1 on the TIP's behalf. Still more complications
result from the possible desirability of including an additional
application (A') and/or an additional graphics package (G') on RH2.
If the simple device is on the Net via a full-fledged local host
(LH), then A, G, and C can each potentially be performed at LH or RH1
-- or RH2 for that matter ("ship it to an E&S for clipping").
In the case of smart devices, C can potentially be performed at the
device itself - - although the TIP may not be able to furnish the
extra socket pair which one would want in order to handle such cases
cleanly. Finally, powerful devices can do G internally but we may
well wish to do A and G over the Net. (Again, how the TIP would
handle such cases was not clear.)
Jim had presented this discussion for the expressed purpose of
getting attention focused on the "ends" of the protocol pipeline
before the meeting became totally concerned with the contents of that
pipeline. We responded in the only possible manner:
CONNECTION PROTOCOL COMMITTEE
A committee was designated to formulate a Graphics Connection
Protocol, the protocol to play an analogous role to that of the
Initial Connection Protocol with respect to the Telnet Protocol.
There was a clearcut consensus that only device-specific codes should
be transmitted over Telnet connections unless the committee uncovered
overwhelmingly convincing arguments to the contrary. The committee
consists of Michener, Bouknight, Harslem, and me. Will Crowther of
BBN will be invited to join the committee to furnish TIP
representation and expertise.
GRAPHICS RESOURCE DOCUMENTATION
Before turning to the protocol specification, it should be pointed
out that most attendees felt that Resource Notebook-like
documentation on Graphics should be prepared. Postel volunteered to
coordinate this effort. Hosts should have drafts submitted to him,
and he will see to getting them published as new portion of the
Resource Notebook. Format considerations were not discussed, but
assumedly the format should imitate that of the main Resource
Notebook sections. Call Jon if you have questions (213-825-2368).
THE PROTOCOL
At the outset of the main protocol discussion, it was agreed that a
committee would be established to resolve those issues on which a
consensus could not be reached at the meeting, and to prepare a draft
of the protocol for distribution to the NGG by year's end. Members
of the committee are Michener, Meyer, Kelly, Cotton, and Liddle.
ASSUMPTIONS
The following assumptions were agreed upon:
1. There shall be a "virtual screen" and a Standard Graphics
Stream.
2. The origin is in the center.
3. Coordinates are signed, 2's complement fractions (-.5 to
+.499).
4. The Standrd Graphics Stream will consist of 8-bit bytes
initially, coordinates are two bytes. ( A "set coordinate size"
operator will be introduced if and when needed.)
5. Network ASCII will be used for text output, with default to
upper case where necessary. Control characters are, for the time
being, site specific.
6. Where appropriate, operators shall have "absolute,"
"relative," and "local" (to a subpicture) modes.
7. The protocol will be organized on a "levels of complexity"
basis, with level 0 comprising operators for simple picture
drawing, level 1 comprising operators for one level of subpicture
definition ("macros", or loosely, "subroutines") and level 2
comprising "viewport" and "window" type operators.
Note that the discussion dealt specifically with graphics OUTPUT.
The Protocol Committee was also empowered to prepare recommendations
for an input-side protocol, but first priority is to be attached to
the formulation of an acceptable output-side protocol.
OPERATORS
As the Protocol Committee's draft is not immediately available, the
following list of low-level operators (the syntax and semantics of
which were discussed at length during the meeting) may be of interest
here:
1. Erase and reset to origin. This operator causes the screen to
be erased and the beam to be positioned at the 0,0 (virtual screen
center) point. A new picture is started.
2. Move. No line is drawn the beam is positioned to the specified
x, y position. There are specific operators for "move relative",
"move absolute" and "move local" modes.
3. Draw. A line (of the current "linetype" -- see 5, below) is
drawn from the present beam position to the specified x, y
position. Modes are as with move. Treatment of the "off-screen"
condition is at the displaying host's option.
4. Point. Display a point at the specified position. Modes are
as with move.
5. Line type. Draw lines of the specified type until further
notice. Currently defined types are solid (0), dashed (1), dotted
(2). If a requested type is not implemented, default to the
next-lower-valued type. After an "erase", type is solid until
changed.
6. Line intensity. Requests line intensity to be as follows: 0 =
off, 128 = normal, 255 = brightest, intermediate values = map
appropriately. After an "erase", intensity is normal until
changed.
7. Text. Cause display of a specified number of specified (Net
ASCII) characters. There are specific operators for "return beam"
after last character (to position before text display) and "leave
beam" (wherever it ends up). Size is to be whatever the
displaying host considers "normal". Treatment of "right-hand
margin" and ASCII controls is host-specified at present. (A
character size operator may be specified later.)
8. Escape. If the console is of specified type, pass a specified
number of bytes directly to it.
Operators for viewports and subpictures were also discussed.
Bouknight and Kelly prepared an BNF treatment of all points
discussed, which will appear in the Protocol Committee's draft.
OTHER BUSINESS
The remaining technical discussion dealt with graphic input, on a
rather general level.
Michener extended the attendees' thanks to Andy Moorer for having
hosted the meeting.
Cotton volunteered to host the next meeting at Mitre, Washington, in
mid-April, at which time we hope to have had enough experience with
the connection protocol and first-pass output protocol to agree on a
"final" statement of them, and to have done enough thinking about the
input side to specify a first-pass protocol for it (unless the
Protocol Committee manages to do so first)
APPENDIX - LIST OF ATTENDEES
Marshall Abrams, Ntl. Bureau of Stds.
Jack Bouknight, U. of Ill.
Jackson T. Cole, Rome Air Development Ctr.
Ira Cotton, MITRE
Daniel Debrosse, UTAH
Eric Harslem, RAND
Karl Kelly, U. of Ill.
David Liddle, Owens Illinois
John Melvin, SRI
Ed Meyer, MAC
James Michener, MAC
James Moorer, SAIL
Hamid Naficy, UCLA
Mike Padlipsky, MAC
Ken Pogran, MAC
Jon Postel, UCLA
Jerry Powell, MITRE
Jean Saylor, SDC
Ron Stoughton, UCSB
Elaine Thomas, BBN
Howard Wactlar, Carnegie-Mellon
Bill White, SUHP
[This RFCwas put into machine readable form for entry]
[into the online RFCarchives by Kelly Tardif, Viagie 10/99]
