RFC 965 (rfc965) - Page 2 of 51
Format for a graphical communication protocol
Alternative Format: Original Text Document
RFC 965 December 1985
A Format for a Graphical Communication Protocol
Most of the work reported in this paper was sponsored by the U.S.
Navy, Naval Electronic Systems Command, Washington D.C., under
Contract No. N00039-83-K-0623.
I. INTRODUCTION
A. Use of a Graphical Communication Protocol
In the field of computer communications, a protocol is a procedure
executed by two cooperating processes in order to attain a
meaningful exchange of information. A graphical communication
protocol is needed to exchange interactive vector graphics
information, possibly in conjunction with other information media
like voice, text, and video. Within this multi-media communication
environment, computer vector graphics plays a key role because it
takes full advantage of the processing capabilities of
communicating computers and human users, and thus it is far more
compact than digital images which are not generated from data
structures containing positional information. Vector graphical
communication trades intensive use of storage and processing, at
the communicating ends, in return for a low volume of exchanged
data, because workstations with graphical hardware exchange
graphics commands in conjunction with large data structures at the
transmitter and receivers. In this manner, the transmission of a
single command can produce extensive changes in the data displayed
at the sending and receiving ends.
It is helpful to situate the aforesaid protocol at one of the
functional levels of the ISO Open Systems Interconnection
Reference Model [1]. Within such a model, a graphical protocol
functionality belongs primarily in the application level, though
some of it fits in the presentation level. We can distinguish the
following components of a communication protocol:
a) a data format
b) rules to interpret transmitted data
c) state information tables
d) message exchange rules
A format for a graphical protocol should provide the layout of the
transmitted data, and indicate how the formated data are
associated with interpretation rules. The choice of format
influences the state tables to be maintained for the correct
processing of the transmitted data stream. The graphical format
has a minor influence on the exchange rules, which should provide
for the efficient use of transmission capacity to transport the
data under such a format. Besides the graphical format, there are
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