Network Working Group                                        W. Hathaway
Request for Comments: 135                                           AMES
NIC: 6712                                                  29 April 1971
Updates: 110


                        Response to NWG/RFC #110
   (Conventions for Using an IBM 2741 Terminal as a User Console for
                    Access to Network Server Hosts)
	
   I would like to propose the following conventions to replace the ones
   proposed in RFC #110.  The original conventions suffer from lack of
   consideration of the correspondence 2741 and what I feel are
   inconsistencies and considerable difficulty of use.  (The 2741
   terminal with correspondence keyboard does not have all of the
   standard characters, notably:

      less than       <
      greater than    >
      logical not    [1]
      vertical bar    |

   Thus we must not use any of these characters in our conventions if we
   wish to support the correspondence 2741.)

   The dedication of certain characters to special functions involves a
   trade-off: the convenience of having the function as a single key
   versus the inconvenience of having to use two keys to enter the
   character as data.  I believe that only two of the special functions
   listed in RFC #110 justify the dedication of a key: the "character
   escape" function and the "character delete" function.  For the
   "character escape" function I recommend the cent sign [2], as this
   character is on both the regular and correspondence 2741 terminals
   and is not in the ASCII character set.  For the "character delete"
   function I recommend the backspace key for obvious reasons.  While
   there is some need to be able to enter the character "backspace" (as
   for underscoring output etc.,) I feel that the trade-off mentioned
   above clearly indicates a single key "character delete" would be much
   more valuable than a single key "backspace" and a two key "character
   delete."

   For the other special functions I recommend two key combinations,
   consisting of "character escape" [2] and a key to define the
   function.  These are summarized below:

      character escape        [2]
      character delete        backspace
      system delete           [2]$
      line delete             [2]# or [2]#NL
      logical line end        [2];
      line continuation       [2]NL
      ASCII control           [2]@

   The option in "line delete" is to allow the user to enter a new line
   (NL) immediately after the "line delete" to line up margins without
   entering a null line; to enter a null line after a "line delete"
   would require two NL characters.

   The two new functions defined above, "line continuation" and "ASCII
   control," are used as follows.  The "line continuation" is used to
   enter a line which is longer than the 2741 carriage (or the margin
   placement) will permit.  It can be looked on as the complement of the
   "logical line end" in that is allows you to enter one logical line on
   several physical lines.

   The use of the "ASCII control" function requires some background.
   There are of course many characters in ASCII which are keyed as
   combinations of "control" and another key.  The "character escape"
   function may be used to handle these control characters as follows: a
   "character escape" followed by a letter will be the equivalent of the
   ASCII "control" "letter", written as Xc (where X is the letter).
   This will greatly simplify the conventions for users, as they will
   simply key "[2]A" where they are used to using Ac and so forth.  For
   completeness, however, there needs to be a way to key the additional
   control characters which require both "control" and "shift" in
   addition to a letter (such as ESC, which is SHIFT Mc).  Further it is
   desirable that a more mnemonic system be provided for the non-
   Teletype user, who knows he wants a LF but does not know that it is a
   Jc.  To satisfy both of these needs I recommend the "ASCII control"
   special function, which is used to enter any of the ASCII control
   character as "[2]@" followed by the standard two or three character
   abbreviation.  Thus "escape" would be [2]@ESC, "line feed" would be
   [2]@LF, and so forth.  The use of the variable length abbreviation
   does not introduce any ambiguity, although from an implementation
   standpoint it may be advantageous to use the two character
   abbreviation proposed in RFC #110.

   Finally we must be able to enter the eight ASCII graphics which do
   not appear on either 2741 terminal, as well as the "cent sign" and
   "backspace" themselves (without their special functions).  For these
   I recommend the following:

      [2](            for     [
      [2])            for     ]
      [2]6            for     {
      [2]9            for     }
      [2]/            for     \
      [2]'            for     '
      [2]"            for     ^
      [2]-            for     ~
      [2][2]          for     [2]
      [2]backspace    for     backspace

   Note that the characters "<" and ">" do not appear on the
   correspondence 2741 and hence should not be used.

Endnotes

   [1] logical not

   [2] cent sign


          [This RFC was put into machine readable form for entry]
          [into the online RFC archives by Lorrie Shiota, 10/02]