Network Working Group C. Stephen Carr
Request for Comments: 15 UTAH
25 September 1969
Network Subsystem for Time Sharing Hosts
Introduction
A set of network primitives has been defined (Network Working Group
Note 11) for inclusion in the monitor systems of the respective
HOSTS. These primitives are at the level of system calls: SPOP's or
BRS's on the 940; UUO's on the PDP-10. Presumably these UUO's are
accessible to all user programs when executing for users whose status
bits allow network access.
In addition to user program access, a convenient means for direct
network access from the terminal is desirable. A sub-system called
"Telnet" is proposed which is a shell program around the network
system primitives, allowing a teletype or similar terminal at a
remote host to function as a teletype at the serving host.
System Primitives
G. Deloche of U.C.L.A. has documented a proposed set of basic network
primitives for inclusion in the operating systems of the respective
HOSTs (NWG Note: 11). The primitives are:
Open primary connection
Open auxiliary connection
Transmit over connection
Close connection.
The details and terminology are defined by Deloche and others in
previous memos. The primitives are system calls, available to
programmers, and are most likely a part of the resident monitor,
rather than the swappable executive.
Basic Terminal Access
In addition to user programming access, it is desirable to have a
subsystem program at each HOST which makes the network immediately
accessible from the teletype without special programming. Subsystems
are commonly used system components such as text editors, compilers
and interpreters. The first network-related subsystem should allow
Carr [Page 1]
RFC 15 Network Subsystem for Time Sharing Hosts September 1969
users at HOST A to connect to HOST B and appear as a regular terminal
user to HOST B. It is expected that more sophisticated subsystems
will be developed in time, but this basic one will render the early
net immediately useful.
Teletype
Terminal ______ ________
_________ | | ______ ______ | |
| | | USER | | | | | |SERVING |
| |-----| HOST |----| |---//---| |---| HOST |
|_________| | A | | | | | | B |
|______| |______| |______| |________|
University Stanford
of Utah Research
Institute
Figure 1: User accesses distant serving HOST via shunt
subsystem in his own Host computer.
Simple Dialogue -- PDP-10 to 940
A user at Utah is sitting at a teletype dialed into the University's
dual PDP-10's. He wishes to operate the CAL sub-system on the 940 at
SRI in Menlo Park, California.
.LOGIN<CR> PDP-10 login
---------
.R TELNET<CR> The PDP-10 run command
------------ is issued to call and start
the TELNET subsystem.
*ESCAPE CHARACTER IS #<CR> The user indicates an escape
------------------------- character which TELNET
will watch for in subsequent
input from the user.
*CONNECT TO SRI<CR> The TELNET subsystem will make
------------------ the appropriate system call
(UUO) to establish a primary
connection. The connection
will be established, provided:
1. SRI is willing to accept
another foreign user;
2. The UTAH user is cleared
for network access at UTAH.
This is determined by a
status word kept in the PDP-10
Carr [Page 2]
RFC 15 Network Subsystem for Time Sharing Hosts September 1969
monitor for each user.
@LOGIN CARR. The user logs in SRI.
-- -----
Characters typed on the user's teletype are transmitted unaltered
through the PDP-10 (user Host) and on to the 940 (serving HOST.)
(The exception to this is a possible one-for-one code conversion
required between the UCLA Sigma 7 and the PDP-10, for example).
@CAL. The PDP-10 TELNET subsystem
- - switches to full duplex,
character-by-character
transmission, since this is
required by 940's. Characters
typed by the user are
underlined. Full duplex
operation is allowed for by
the PDP-10, though not used
by most DEC subsystems.
The user wishes to load a CAL file into 940 CAL from the file system
on his local PDP-10.
CAL AT YOUR SERVICE
>READ FILE FROM NETWRK. 'NETWRK' is a predefined
---------------------- 940 name similar to PAPER
TAPE OR TELETYPE. The 940
file opening BRS is set to
expect an auxiliary connection
and the file from UTAH.
#NETWRK: <- DSK:MYFILE.CAL<CR> The user types the prescribed
----------------------------- escape character, followed by
the TELNET command, to send
the desired file to SRI on an
auxiliary connection. The
user's next statement is in
CAL again.
The Telnet Subsystem
The Telnet subsystem coding should fit easily into one core page, for
it does very little. It effectively establishes a shunt in the user
HOST between the remote user and the serving HOST. Telnet commands
are:
Carr [Page 3]
RFC 15 Network Subsystem for Time Sharing Hosts September 1969
ESCAPE CHAR IS ___________<CR> Declares a character which
Telnet will watch for.
Subsequent strings typed
between this character and
a carriage return are not
shunted through to the serving
host, but sent instead to the
Telnet program in the user's
local HOST.
This escape character is not the same as the user's host
rubout character.
CONNECT TO __________________<CR> The official site name of the
desired serving HOST is typed
(i.e.: SRI, UTAH, UCLA, UCSB).
Telnet attempts to establish a
connection. If the attempt is
successful, the following
characters are shunted through
the user's local machine. The
connection places the user in
the pre-logged in state at
the serving HOST.
LOGOUT<CR> Telnet issues the logout command
sequence to the serving HOST.
If the user simply rubs out and
kills his PDP-10 job, the
PDP-10 will indicate to the 940
that the connection is closed.
The 940 system primitives do
whatever they do when a normal
dataphone connection is
suddenly broken.
COPY FILE A file copying command is
available in TELNET to
move data along on auxiliary
connections from the
user's HOST file system
to the serving HOST.
Carr [Page 4]
RFC 15 Network Subsystem for Time Sharing Hosts September 1969
These TELNET commands are accepted when the TELNET subsystem is first
entered or following the declared escape character.
CONCLUSION
Given the basic system primitives, the TELNET subsystem at the user
host and a manual for the serving host, the network can be
profitably employed by a remote user. TELNET subsystem constitutes a
"level 0" network program which will quickly be surpassed. It is,
however, simple enough to be working fairly soon.
[Editor's note: <CR> has been used in this document to indicate end-
of-line, in place of the original handwritten arrows.]
[ This RFC was put into machine readable form for entry ]
[ into the online RFC archives by Sergio Kleiman 9/00 ]
