RFC 357 (rfc357) - Page 2 of 13

Echoing strategy for satellite links

RFC 357         An Echoing Strategy For Satellite Links        June 1972


   knows the syntax of the string it expects, it can specify to the
   Terminal Handler those characters which delimit completed parameters.
   Such characters are called 'Wakeup Characters' since the user process
   is awakened as they are echoed.

   Certain commands keyed by the user will require an output response
   from the process.  In order that the typed commands be followed by
   its response and be separated from succeeding commands, the Terminal
   Handler must suspend echoing of user type-ahead.  It can resume
   echoing (starting for type-ahead - with the unechoed characters in
   the buffer) as soon as the process has stated (implicitly or
   explicitly) that it has completed the output response.

   Characters which cause the Terminal Handler to suspend echoing are
   called 'break characters' They are specified by the user process
   based upon the syntax of the expected input.  Normally break
   characters are also wakeup characters.  As examples:

      1. A text editor may gobble up typed English sentences every time
         a period or question mark is echoed.  The two characters are
         wakeup characters only.  There is no need to suspend echoing.

      2. In some systems, an ESC character is used to invoke command
         recognition.  The user who types

               CO [ESC] ABC [ESC] XYZ

         should see as output

            COPY (FROM FILE) ABC (TO FILE) XYZ

         The ESC is both a break and a wakeup.  The printout should be
         the same no matter how fast the user types.

   The server must provide a means for each user process to communicate
   the following to the Terminal Handler:

      1. the set of wakeup characters,
      2. the set of break characters,
      3. which break characters should and which should not be echoed,
         (Some break characters - such as ESC in example 2 - should not
         be echoed).
      4. completion of an output response,
      5. whether or not to echo characters. (Not echoing is useful in
         "hide your input" applications.)






Davidson