SUPDUP Protocol
RFC 734

Document Type RFC - Historic (October 1977; No errata)
Last updated 2013-03-02
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NWG/RFC# 734                                    MRC 07-OCT-77 08:46  41953
SUPDUP Display Protocol                                             Page 1

Network Working Group                                         Mark Crispin
Request for Comments 734                                             SU-AI
NIC 41953                                                   7 October 1977

                          SUPDUP Protocol


This document describes  the SUPDUP protocol,  a highly efficient  display
telnet protocol.  It originally started as a private protocol between  the
ITS systems at MIT to allow a user at any one of these systems to use  one
of the others as a display.  At the current writing, SUPDUP user  programs
also exist  for  Data  Disc  and  Datamedia  displays  at  SU-AI  and  for
Datamedias at SRI-KL.  The author is not aware of any SUPDUP servers other
than at the four MIT ITS sites.

The advantage  of  the  SUPDUP  protocol  over  an  individual  terminal's
protocol is that SUPDUP defines a "virtual" or "software" display terminal
that implements relevant  cursor motion operations.   The protocol is  not
built on  any  particular  display  terminal but  rather  on  the  set  of
functions common to all display terminals; hence it is completely  device-
independent.  In addition, the protocol also provides for terminals  which
cannot handle certain operations, such as line or character insert/delete.
In fact,  it is  more than  this.   It provides  for terminals  which  are
missing any set of features, all the way down to model 33 Teletypes.

The advantage over the TELNET protocol  is that SUPDUP takes advantage  of
the full  capabilities of  display  terminals, although  it also  has  the
ability to run printing terminals.

It is to be  noted that SUPDUP operates  independently from TELNET; it  is
not an option to  the TELNET protocol.   In addition, certain  assumptions
are made about the  server and the user  programs and their  capabilities.
Specifically, it is  assumed that the  operating system on  a server  host
provides all the display-oriented features of ITS.  However, a server  may
elect not to do certain display operations available in SUPDUP; the SUPDUP
protocol is far-reaching enough so  that the protocol allows terminals  to
be handled  as well  as that  host can  handle terminals  in general.   Of
course, if a host does not  support display terminals in any special  way,
there is no point in bothering  to implement a SUPDUP server since  TELNET
will work just as well.

A more complete description  of the display facilities  of SUPDUP and  ITS
can be found by FTP'ing the  online file .INFO.;ITS TTY from ARPAnet  host
MIT-AI (host 206 octal, 134. decimal).  For more information, the  mailing
address for SUPDUP is "(BUG SUPDUP) at MIT-AI".  If your mail system won't
allow you to use parentheses, use Bug-SUPDUP@MIT-AI.

NWG/RFC# 734                                        MRC 07-OCT-77 08:46  41953
SUPDUP Display Protocol                                             Page 2


The SUPDUP protocol originated as the internal protocol used between parts
of ITS, and between ITS and "intelligent" terminals.  Over the network,  a
user host acts like an intelligent terminal programmed for ITS.

The way terminal  output works  in ITS is  as follows:   The user  program
tells the system to  do various operations,  such as printing  characters,
clearing the screen, moving the cursor, etc.  These operations are  formed
into 8-bit characters  (using the  %TD codes described  below) and  stored
into a  buffer.   At interrupt  level,  as the  terminal  demands  output,
characters are  removed  from  the buffer  and  translated  into  terminal
dependent codes.  At this time  padding and cursor motion optimization are
also done.

In some cases, the interrupt side does not run on the same machine as  the
user program.  SUPDUP terminals have their "interrupt side" running in the
user host.  When  SUPDUP is  run between two  ITS's, the  SUPDUP user  and
server programs and the network simply move characters from the buffer  in
the server machine to the buffer in the user machine.  The interrupt  side
then runs on the user machine just as if the characters had been generated

Due to the highly interactive characteristics of both the SUPDUP  protocol
and the ITS system, all transactions are strictly character at a time  and
all echoing  is  remote.  In  addition,  all padding  and  cursor  control
optimization must be done by the user.

Because this is also the internals of ITS, the right to change it any time
if necessary to provide new features  is reserved by MIT.  In  particular,
the initial  negotiation  is probably  going  to be  changed  to  transmit
additional variables, and additional %TD codes  may be added at any  time.
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