Some historic moments in networking
RFC 89

Document Type RFC - Unknown (January 1971; Errata)
Last updated 2013-03-02
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Network Working Group                                        B. Metcalff
Request for Comments: 89                                           MITDG
NIC: 5697                                                19 January 1971


   While awaiting the completion of an interim network control program
   (INCP) for the MIT MAC Dynamic Modeling/Computer Graphics PDP-6/10
   System (MITDG), we were able to achieve a number of 'historic moments
   in networking' worthy of some comment.  First, we were able to
   connect an MITDG terminal to a Multics process making it a Multics
   terminal.  Second, we successfully attached an MITDG terminal to the
   Harvard PDP-10 System thereby enabling automatic remote use of the
   Harvard System for MIT.  Third, we developed primitive mechanisms
   through which remotely generated programs and data could be
   transmitted to our system, executed, and returned.  Using these
   mechanisms in close cooperation with Harvard, we received graphics
   programs and 3D data from Harvard's PDP-10, processed them repeatedly
   using our Evans & Sutherland Line Drawing System (the E&S), and
   transmitted 2D scope data to Harvard's PDP-1 for display.


   Our experiments were run on the MITDG PDP-6/10 using what we have
   affectionately called our 'interim interim NCP' (IINCP).  Under the
   IINCP the IMP Interface is treated as a single-user I/O device which
   deals in raw network messages.  The software supporting necessary
   system calls includes little more than the basic interrupt-handling
   and buffering schemes to be used later by the NCP.  In short, the
   user-level programs which brought us to our historic moments were
   written close to the hardware with full knowledge of IMP-HOST
   Protocol (BBN 1822).  When the INCP and NCP are completed, these
   programs can be pruned considerably (80%).  The exercise of writing
   programs which conform to IMP-HOST Protocol was not at all wasted.
   Only now can those of us who are not writing the NCP begin to grasp
   the full meaning of RFNM's and their use in flow control.  The
   penalties for ignoring an impatient IMP, for failing to send NOOPS
   (NO-OPS) when starting up, and for blasting data onto the Network
   without regard for RFNM's are now well understood.

The Multics Connection

   Our quest for historic moments began with the need to demonstrate
   that the complex hardware-software system separating MITDG and
   Multics was operative and understood.  A task force (Messrs. Bingham,

Metcalff                                                        [Page 1]
RFC 89            SOME HISTORIC MOMENTS IN NETWORKING    19 January 1971

   Brodie, Knight, Metcalfe, Meyer, Padlipsky and Skinner) was
   commissioned to establish a 'polite conversation' between a Multics
   terminal and an MITDG terminal.

   It was agreed that messages would be what we call 'network ASCII
   messages': 7-bit ASCII characters right-adjusted in 8-bit fields
   having the most significant bit set, marking, and padding.  In that
   Multics is presently predisposed toward line-oriented half-duplex
   terminals, it was decided that all transmissions would end with the
   Multics EOL character (ASCII <LINE FEED>).  To avoid duplicating much
   of the INCP in our experiment, the PDP-10 side of the connection was
   freed by convention from arbitrary bit-stream concatenation
   requirements and was permitted to associate logical message
   boundaries with network message boundaries (sic).  The 'polite
   conversation' was thus established and successful.

   Multics, then, connected the conversation to its command processor
   and the PDP-10 terminal suddenly became a Multics terminal.  But, not

   First, in the resulting MITDG-Multics connection there was no
   provision for a remote QUIT, which in Multics is not an ASCII
   character.  This is a problem for Multics.  It would seem that an
   ASCII character or the network's own interrupt control message could
   be given QUIT significance.

   Second, our initial driver program did not provide for RUBOUT.
   Because the Multics network input stream bypassed the typewriter
   device interface module (TTYDIM), line canonicalization was not
   performed.  In a more elegant implementation, line canonicalization
   could be done at Multics, providing the type-in editing conventions
   familiar to Multics users.  We fixed this problem hastily by having
   our driver program do local RUBOUT editing during line assembly, thus
   providing type-in editing conventions familiar to MITDG users.  It is
   clearly possible to do both local type-in editing and distant-host
   type-in editing.

   Third, we found that because of the manner in which our type-in
   entered the Multics system under the current network interface (i.e.
   not through TTYDIM), our remotely controlled processes were
   classified 'non-interactive' and thus fell to the bottom of Multics
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