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
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.