For example, if a user at a terminal causes an AO to be
      transmitted, the server which receives the AO (if it provides that
      function at all) should return a Synch to the user.

      Finally, just as the TCP Urgent notification is needed at the
      TELNET level as an out-of-band signal, so other protocols which
      make use of TELNET may require a TELNET command which can be
      viewed as an out-of-band signal at a different level.



 


RFC 854                                                         May 1983


      By convention the sequence [IP, Synch] is to be used as such a
      signal.  For example, suppose that some other protocol, which uses
      TELNET, defines the character string STOP analogously to the
      TELNET command AO.  Imagine that a user of this protocol wishes a
      server to process the STOP string, but the connection is blocked
      because the server is processing other commands.  The user should
      instruct his system to:

         1. Send the TELNET IP character;

         2. Send the TELNET SYNC sequence, that is:

            Send the Data Mark (DM) as the only character
            in a TCP urgent mode send operation.

         3. Send the character string STOP; and

         4. Send the other protocol's analog of the TELNET DM, if any.

      The user (or process acting on his behalf) must transmit the
      TELNET SYNCH sequence of step 2 above to ensure that the TELNET IP
      gets through to the server's TELNET interpreter.

         The Urgent should wake up the TELNET process; the IP should
         wake up the next higher level process.

   THE NVT PRINTER AND KEYBOARD

      The NVT printer has an unspecified carriage width and page length
      and can produce representations of all 95 USASCII graphics (codes
      32 through 126).  Of the 33 USASCII control codes (0 through 31
      and 127), and the 128 uncovered codes (128 through 255), the
      following have specified meaning to the NVT printer:

         NAME                  CODE         MEANING

         NULL (NUL)              0      No Operation
         Line Feed (LF)         10      Moves the printer to the
                                        next print line, keeping the
                                        same horizontal position.
         Carriage Return (CR)   13      Moves the printer to the left
                                        margin of the current line.









 


RFC 854                                                         May 1983


         In addition, the following codes shall have defined, but not
         required, effects on the NVT printer.  Neither end of a TELNET
         connection may assume that the other party will take, or will
         have taken, any particular action upon receipt or transmission
         of these:

         BELL (BEL)              7      Produces an audible or
                                        visible signal (which does
                                        NOT move the print head).
         Back Space (BS)         8      Moves the print head one
                                        character position towards
                                        the left margin.
         Horizontal Tab (HT)     9      Moves the printer to the
                                        next horizontal tab stop.
                                        It remains unspecified how
                                        either party determines or
                                        establishes where such tab
                                        stops are located.
         Vertical Tab (VT)       11     Moves the printer to the
                                        next vertical tab stop.  It
                                        remains unspecified how
                                        either party determines or
                                        establishes where such tab
                                        stops are located.
         Form Feed (FF)          12     Moves the printer to the top
                                        of the next page, keeping