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rfc:rfc282

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 RFC describing 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

Padlipsky [Page 1] RFC 282 Graphics Meeting Report December 1971

 "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.

Padlipsky [Page 2] RFC 282 Graphics Meeting Report December 1971

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."

Padlipsky [Page 3] RFC 282 Graphics Meeting Report December 1971

 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 RFC describing 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").

Padlipsky [Page 4] RFC 282 Graphics Meeting Report December 1971

 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.

Padlipsky [Page 5] RFC 282 Graphics Meeting Report December 1971

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.

Padlipsky [Page 6] RFC 282 Graphics Meeting Report December 1971

    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)

Padlipsky [Page 7] RFC 282 Graphics Meeting Report December 1971

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 RFC was put into machine readable form for entry]
   [into the online RFC archives by Kelly Tardif, Viagénie 10/99]

Padlipsky [Page 8]

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