Decode Encode Language (DEL)
RFC 5

Document Type RFC - Unknown (June 1969; Errata)
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Network Working Group                                           4691
RFC-5                                                           Jeff Rulifson
                                                                June 2, l969

                                DEL

:DEL, 02/06/69 1010:58   JFR   ;   .DSN=1; .LSP=0; ['=] AND NOT SP ; ['?];
dual transmission?

ABSTRACT

   The Decode-Encode Language (DEL) is a machine independent language
   tailored to two specific computer network tasks:

      accepting input codes from interactive consoles, giving immediate
      feedback, and packing the resulting information into message 
      packets for network transmissin.

      and accepting message packets from another computer, unpacking
      them, building trees of display information, and sending other
      information to the user at his interactive station.

   This is a working document for the evolution of the DEL language.
   Comments should be made through Jeff Rulifson at SRI.

FORWARD

   The initial ARPA network working group met at SRI on October 25-26,
   1968.

      It was generally agreed beforehand that the runmning of interactive
      programs across the network was the first problem that would be
      faced.

      This group, already in agreement about the underlaying notions of
      a DEL-like approach, set down some terminology, expectations for
      DEL programs, and lists of proposed semantic capability.

      At the meeting were Andrews, Baray, Carr, Crocker, Rulifson, and
      Stoughton.

   A second round of meetings was then held in a piecemeal way.

      Crocker meet with Rulifson at SRI on November 18, 1968.  This
      resulted in the incorporation of formal co-routines.

      and Stoughton meet with Rulifson at SRI on Decembeer 12, 1968.  It
      was decided to meet again, as a group, probably at UTAH, in late
      January 1969.

   The first public release of this paper was at the BBN NET meeting in
   Cambridge on February 13, 1969.

NET STANDARD TRANSLATORS        

   NST   The NST library is the set of programs necessary to mesh
   efficiently with the code compiled at the user sites from the DEL
   programs it receives.  The NST-DEL approach to NET interactive system
   communication is intended to operate over a broad spectrum.

   The lowest level of NST-DEL usage is direct transmission to the
   server-host, information in the same format that user programs
   would receive at the user-host.

      In this mode, the NST defaults to inaction.  The DEL program
      does not receive universal hardware representation input but 
      input in the normal fashion for the user-host.

      And the DEL 1 program becomes merely a message builder and
      sender.

   A more intermediate use of NST-DEL is to have echo tables for a
   TTY at the user-host.

      In this mode, the DEL program would run a full duplex TTY for
      the user.

      It would echo characters, translate them to the character set 
      of the server-host, pack the translated characters in messages,
      and on appropriate break characters send the messages.

      When messages come from the server-host, the DEL program would
      translate them to the user-host character set and print them on
      his TTY.

   A more ambitious task for DEL is the operation of large,
   display-oriented systems from remote consoles over the NET.

      Large interactive systems usually offer a lot of feedback to
      the user.  The unusual nature of the feedback make it
      impossible to model with echo table, and thus a user program
      must be activated in a TSS each time a button state is changed.

         This puts an unnecessarily large load on a TSS, and if the
         system is being run through the NET it could easily load two
         systems.

         To avoid this double overloading of TSS, a DEL program will
         run on the user-host.  It will handle all the immediate
         feedback, much like a complicated echo table.  At appropriate
         button pushes, message will be sent to the server-host and
         display updates received in return.

      One of the more difficult, and often neglected, problems is the
      effective simulation of one nonstandard console on another non-
      standard console.

         We attempt to offer a means of solving this problem through
         the co-routine structure of DEL programs.  For the
         complicated interactive systems, part of the DEL programs
         will be constructed by the server-host programmers.
         Interfaces between this program and the input stream may
         easily be inserted by programmers at the user-host site.

UNIVERSAL HARDWARE REPRESENTATION

   To minimize the number of translators needed to map any facility's
   user codes to any other facility, there is a universal hardware
   representation.

   This is simply a way of talking, in general terms, about all the
   hardware devices at all the interactive display stations in the initial
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