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Network Working Group C. Stephen Carr Request for Comments: 15 UTAH

                                                    25 September 1969
              Network Subsystem for Time Sharing Hosts


 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.
  Terminal        ______                                 ________
  _________      |      |     ______          ______    |        |
 |         |     | USER |    |      |        |      |   |SERVING |
 |         |-----| HOST |----|      |---//---|      |---| HOST   |
 |_________|     |  A   |    |      |        |      |   |  B     |
                 |______|    |______|        |______|   |________|
                University                               Stanford
                 of Utah                                 Research
 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
    1. —————– 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,
                                     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.
 >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

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

      On the 940 this is:
 COPY <file name> TO NETWRK.
 -                   -     -
      On the PDP-10:
 NETWRK <- DSK: <file name>
 These TELNET commands are accepted when the TELNET subsystem is first
 entered or following the declared escape character.


 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  ]

Carr [Page 5]

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