TELNET Command at Host LL
RFC 452

Document Type RFC - Unknown (February 1973; No errata)
Last updated 2013-03-02
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Network Working Group                                          J. Winett
Request for Comments: 452                                            JMW
NIC: 14136                                               8 February 1973

                       TELNET Command at Host LL

   The attached writeup documents the use of the TELNET command at Host
   LL for uses under the CP/CMS time-sharing system.  This command
   provides for use in a HALF DUPLEX or FULL DUPLEX mode and can be used
   with ASCII codes or with EBCDIC codes (i.e., transparent mode).  The
   keyboard conventions allow for entering all ASCII codes using a
   CONTROL character followed by another character for the codes not
   present on an IBM 2741 terminal.  In addition a number of local
   TELNET control commands have been defined which allows the mode of
   operation to be changed, the redefinition of special characters, the
   sending of TELNET control codes, as well as for obtaining input from
   a file instead of from the terminal.  These later features provide
   for a rudimentary file transfer facility.

   This material has not been reviewed for public release and is
   intended only for use with the ARPA network.  It should not be quoted
   or cited in any publication not related to the ARPA network.

   TELNET

   Purpose:

      To access another terminal oriented system on the ARPA network.

   Format:

      TELNET host <tag> RESUME     EBCDIC      HALFDUP
                    1    OPEN       ASCII      FULLDUP

      host - either the hexadecimal code for a foreign network service
              site or a standard mnemonic for a foreign site.  See
              Figure 1.

      tag - the identifier for the local connections to the network.
              The tag is used together with the address of the virtual
              machine descriptor table (UTABLE) to form local socket
              numbers which are used in the network protocol.

      RESUME - used to reactivate communications with a foreign site
              after having previously left the TELNET command leaving
              the connections open.

Winett                                                          [Page 1]
RFC 452                TELNET Command at Host LL           February 1973

      EBCDIC - to communicate with EBCDIC codes.  The default is network
              ASCII.

      HALFDUP - to operate under a half duplex protocol, i.e. with a
              locked keyboard.

              The EBCDIC HALFDUP the protocol assumes that the TELNET
              break code (circle C) will be received to indicate when
              the keyboard should be locked for input.

              In ASCII HALFDUP the keyboard will lock after a line of
              input and will unlock after one or more lines have been
              received for output.  An external interrupt will also
              unlock a locked keyboard.

              The default is full duplex where the keyboard is always
              unlocked for input.  A null line is required to
              temporarily lock the keyboard in order to receive output.

   Usage:

      A number of hosts on the ARPA network provide TELNET service.  A
      Network Virtual Terminal (NVT) has been specified so that using
      sites can write one TELNET program which maps a local terminal
      into the NVT to access any serving site on the network.  Once
      communication has been established between a using site and a
      serving site, keyed input is sent to the serving system and output
      from the serving site, when received, is typed on the local
      terminal.

      The NVT protocol requires that the keyboard be capable of entering
      all of the 128 ASCII codes together with a number of the TELNET
      control codes.  To support an NVT with an IBM 2741 terminal, it is
      necessary to adapt a control convention for entering codes which
      are not associated with single keys on the keyboard.  In addition,
      since CP/CMS processes input from a 2741 on a line at a time
      terminated with a newline, a means must be establish for entering
      a sequence of characters for transmission which is not terminated
      with a newline code.

      When TELNET is initiated the message

                           ENTER CONTROL CHARACTER

      is typed.  A non-blank character should then be entered which
      defines the character which, in combination with another
      character, will be used to enter codes not associated with single

Winett                                                          [Page 2]
RFC 452                TELNET Command at Host LL           February 1973

      keys.  The control character is also used for other special
      control functions as described below.

   Codes:

      The NVT usually requires that characters be transmitted in an
      eight bit ASCII code.  Since the TELNET command is written to
      process EBCDIC codes ASCII codes received are translated into
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