📄 rfc549.txt
字号:
Network Working Group AnonymousRequest for Comments: 549 Center for Advanced Computation, U of IllNIC: 17795 15-17 July 1973 MINUTES OF NETWORK GRAPHICS GROUP MEETINGSunday evening, 15 July The meeting came to order around 1930, Jim Michener presiding. After introductions, an agenda was constructed for the rest of the meeting. Elaine Thomas distributed copies of an Alternative Network Graphics Protocol for attendees to read overnight prior to discussion. Because some individuals were absent who had definitely indicated that they were coming Monday morning, the meeting was adjourned at 2030 after deciding to meet at 0930 the next morning.Monday Morning/Afternoon, 16 July The meeting was called to order at 0930 Jim Michener distributed an outline of a paper describing desirable facilities for the use of two dimensional input devices with a hierarchically structured display program. Ken Victor distributed copies of RFC 553: A Proposed Network Text/Graphics Protocol. (LJOURNAL,17810,) Ken Pogran described the history of the NGG and how the "levels" approach of RFC 493 came about. In particular, the "level 0" protocol was an attempt to define something to experiment with, but with the thought that it should be possible to imbed "level 0" meaningfully in any later protocol. Reports of Network Graphics Experiences Jon Jervert described the installation at CAD/CAM (Fort Monmouth). They have a spectrum of display terminals and have tried several via a Telnet connection to MIT-DMCG. They experienced unacceptable slowness with a 300 Baud bandwidth. Austin Henderson described an Air Traffic Control experiment in which the simulator receives codes describing changes in state and generates descriptions of the air space (region) being controlled [Page 1] RFC 549 Minutes of Network Graphics 15-17 July 1973 and aircraft position and velocity. These descriptions are highly encoded--they are not pictures in any general sense. The rate at which the simulation proceeded was adequate. Jim Michener described the results of an experiment in which the E&S LDS-1 at MIT-DMCG was used to generate stylus inking input for a character recognition program at SDC. The experiment was plagued with difficulties including bugs in SDC's NCP and scheduling of experimental/debugging sessions. When the experiment was finally terminated (due to planned extensive hardware modifications at DMCG) a clear understanding had not yet emerged, but apparently network transmission delays had been experienced of up to 20 seconds. Dan Cohen described an Aircraft Flight Simulator which interacts with a user at the Harvard PDP-1. The simulation takes place on a PDP-10. Network traffic is approximately 200 bits from the PDP-1 to the PDP-10 and several thousand bits in the opposite direction. It has been found that at least 5 updates are required per second to give the "pilot" an adequate feeling of control. The Harvard PDP-10 and one at BBN have been used, the latter at 6 AM to avoid loading problems. John Pickens described UCSB's status regarding output in level 0 Network Graphics Protocol (NGP-0). Steve Bunch reported that he has an Imlac monitor which accepts NGP-0 directly. Programs have been developed at CCN (using subroutine packages modeled after plotter packages) which build files containing pictures in NGP-0. Other programs output the pictures either to a Gould plotter or a storage display (in device specific code) or to an Imlac (in NGP-0 form). Steve Holmgren briefly described a Fancy Arpa Network Graphics System (FANGS) under development at UCSD. Discussion of Modifications in the Graphics Protocol David Egli reported that he and Jim Foley (of Univ. of North Carolina) thought that the graphics protocol should have the ability to replace items, and that 3 dimensional data should be allowable. Jim Foley also thinks that a subpicture call should be able to specify a rate of rotation, scaling, and translation, in addition to initial values for these. An extended coffee break followed to allow perusal of the documents distributed. [Page 2] RFC 549 Minutes of Network Graphics 15-17 July 1973 Elaine Thomas summarized her protocol proposal for a hierarchically structured, editable display file. Discussion related to the levels approach of RFC 493 concluded that levels were inappropriate; we would henceforth think in terms of negotiable options. Ken Victor stressed that NLS was particularly desirous of being able to make use of the graphics protocol; that was the reason for their developing RFC 553. Ken Pogran observed that a structures display system as is being proposed is more a distributed graphics system than a protocol, and that he thought this a good idea. General consensus agreed with him. Jim Michener described proposals for input. He emphasized the necessity of transmitting position information in figure coordinates as opposed to screen coordinates or top level figure coordinates. Bob Sproul described two different ways in which a graphics application in a serving host can communicate to a using host controlling a display device. If the using host has complex enough software or hardware, a structured definition of the display may be sent. A structured display definition consists of figures (also called pictures or groups) which consist of units. A unit is either a call to another figure or a collection of one or more text or graphic commands. (Other special purpose units may exist, also.) Figures and units have names and may be created, replaced and deleted (and other things). A simpler scheme for the using host is that transformed segmented display information be sent across the network. Segments have names and can be individually created, replaced and deleted. Either the application works directly in terms of segments, or it works in terms of a structures display definition and software at the serving host has the responsibility of evaluating the transformations and the sub-figure calls. [Page 3] RFC 549 Minutes of Network Graphics 15-17 July 1973 It seems likely that such transformation software might have to exist at the serving host anyway if that host has any graphics terminals of small to moderate capability. It was agreed to restrict our attention to the simpler "transformed-segmented" scheme, and delay consideration of the "hierarchically structured" scheme until another meeting. It seemed to the meeting that a significant number of applications would need nothing more powerful than a segmented scheme. One desirable mechanism is an "end batch of updates" command. It can help optimize the use of a storage terminal and it can let a user program causes fixes to occur on a refresh tube all at once. After lunch, Ira Cotton pointed out that it would be easy enough to allow NGP-0 to be upward compatible with a segmented, transformed scheme. Bob Sproul agreed and said that that was a good argument for sending only device independent data on the net. (This idea was modified in discussion on Tuesday.) Ken Victor discussed TTY units, a mechanism for displaying characters which are "unescorted" i.e., are not part of a graphics "text" command. In particular they are for spontaneous messages from the operating system (like "out of funds" or "going down in 5 min"). General discussion was undecided on whether TTY units should really be part of a graphics protocol. (This was later decided affirmatively.) It was noted that unescorted characters coming from the serving host could probably be handled, but that those coming from the using host might not be.Discussion of Network Connection for Graphics A graphics connection may start out with a Telnet connection. We will request a DO GRAPHICS telnet option. Multiplexing on the Telnet connection vs using a separate connection pair. Dan Cohen stated that his Flight Simulator uses a second pair. Alex McKenzie pointed out that some hosts have only "read and block" input commands, not "read and continue". This means we cannot demand to have separate connection pairs with graphics on one and telnet-type information on the other. [Page 4] RFC 549 Minutes of Network Graphics 15-17 July 1973 Jim Hansen called for a show of hands of preferences: NLS was the only site against using multiple connection. Several sites were against multiplexing graphics information on the Telnet connection. Issues included: It is easier to merge two streams at the user than to split one into two. The latter requires "smart" programming. TIP users may lose if multiple connections are required. It should be possible to do it on one connection. In summary: two connections are better than one, the number shall be negotiated over the Telnet connection. Ira Cotton asked for a discussion of connection initiation other than via a Telnet connection. It was agreed that we did not know enough at this time to specify this and that it was a matter for experimentation. Someone commented that what we have is a Network Virtual Graphics Terminal which has a Network Virtual Keyboard and a Network Virtual Printer (in the Telnet sense) and a Network Virtual Display Unit. The printer and the display unit may be the same. Ira Cotton announced that Jim Foley (of Univ. of North Carolina) is planning to have a workshop on machine independent graphics under the auspices of SIGGRAPH in Washington D.C. around mid-April (cherry blossom time).Discussion of Graphics Input Dan Cohen summarized the use of input in his flight simulator: since it comprises only approximately 200 bits in toto, all switches, knobs, and stylus position are transmitted. This takes place about five times per second. Austin Henderson described the input facilities on the LL TX-2. Attentions are enabled. What information will be desired when a particular attention occurs is described at the time the attention is enabled. When an attention occurs, the system records the desired information in a queue for the application program. When the application program is next scheduled it examines the queue and responds as it sees fit. [Page 5] RFC 549 Minutes of Network Graphics 15-17 July 1973 It was generally agreed to adopt the TX-2 strategy. Input devices will not be enabled unless the server does so. No restriction is placed on any "lies" the using host wishes to make regarding disguising one device as another. Network connections for input follow the same rules as for output. What input attentions are implemented at the using host may be determined by the serving host in response to an inquiry. Inking will be provided by the using host (but only one inking input can be specified at a time; no buffering ahead shall be done by the using host). Tracking means the feedback of the current two dimensional input device position to the user. This is automatically turned on by Inking, Positioning, and Targeting (hitting) attentions. What data are reported at the time of an attention is specified by the application at the server when the attention is enabled. Types of attentions were listed and also what additional optional information could be specified with each. Deactivating Inputs was discussed. It is possible for the application to explicitly deactivate an attention. When an attention is enabled it shall be possible to specify when it should be deactivated. Three modes were mentioned: Never turned off (until the application explicitly does so), turned off when it occurs (self-destruct), turned off when any attention occurs. The need for a synchronization message was agreed upon. It was agreed that the serving host - using host relationship would be one of master - slave. Among other things, the using host would never volunteer input information which the serving host (application) had not asked for. It was decided to meet the next morning at 0830 The meeting adjourned about 1830 [Page 6]⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -