The recipient should delete the last preceding undeleted
         character or "print position" from the data stream.

      Erase Line (EL)

         The recipient should delete characters from the data stream
         back to, but not including, the last "CR LF" sequence sent over
         the TELNET connection.

      The spirit of these "extra" keys, and also the printer format
      effectors, is that they should represent a natural extension of
      the mapping that already must be done from "NVT" into "local".
      Just as the NVT data byte 68 (104 octal) should be mapped into
      whatever the local code for "uppercase D" is, so the EC character
      should be mapped into whatever the local "Erase Character"
      function is.  Further, just as the mapping for 124 (174 octal) is
      somewhat arbitrary in an environment that has no "vertical bar"
      character, the EL character may have a somewhat arbitrary mapping
      (or none at all) if there is no local "Erase Line" facility.
      Similarly for format effectors:  if the terminal actually does
      have a "Vertical Tab", then the mapping for VT is obvious, and
      only when the terminal does not have a vertical tab should the
      effect of VT be unpredictable.

TELNET COMMAND STRUCTURE

   All TELNET commands consist of at least a two byte sequence:  the
   "Interpret as Command" (IAC) escape character followed by the code
   for the command.  The commands dealing with option negotiation are
   three byte sequences, the third byte being the code for the option
   referenced.  This format was chosen so that as more comprehensive use
   of the "data space" is made -- by negotiations from the basic NVT, of
   course -- collisions of data bytes with reserved command values will
   be minimized, all such collisions requiring the inconvenience, and




 


RFC 854                                                         May 1983


   inefficiency, of "escaping" the data bytes into the stream.  With the
   current set-up, only the IAC need be doubled to be sent as data, and
   the other 255 codes may be passed transparently.

   The following are the defined TELNET commands.  Note that these codes
   and code sequences have the indicated meaning only when immediately
   preceded by an IAC.

      NAME               CODE              MEANING

      SE                  240    End of subnegotiation parameters.
      NOP                 241    No operation.
      Data Mark           242    The data stream portion of a Synch.
                                 This should always be accompanied
                                 by a TCP Urgent notification.
      Break               243    NVT character BRK.
      Interrupt Process   244    The function IP.
      Abort output        245    The function AO.
      Are You There       246    The function AYT.
      Erase character     247    The function EC.
      Erase Line          248    The function EL.
      Go ahead            249    The GA signal.
      SB                  250    Indicates that what follows is
                                 subnegotiation of the indicated
                                 option.
      WILL (option code)  251    Indicates the desire to begin
                                 performing, or confirmation that
                                 you are now performing, the
                                 indicated option.
      WON'T (option code) 252    Indicates the refusal to perform,
                                 or continue performing, the
                                 indicated option.
      DO (option code)    253    Indicates the request that the
                                 other party perform, or
                                 confirmation that you are expecting
                                 the other party to perform, the
                                 indicated option.
      DON'T (option code) 254    Indicates the demand that the
                                 other party stop performing,
                                 or confirmation that you are no
                                 longer expecting the other party
                                 to perform, the indicated option.
      IAC                 255    Data Byte 255.








 


RFC 854                                                         May 1983