    D. Crocker (UCLA-NMC)
    RFC 657, NIC 31160 (Oct. 25, 1974)
    Online file: [ISI]<DCROCKER>NAOVTD.TXT

                TELNET OUTPUT VERTICAL TAB DISPOSITION OPTION

    1. Command name and code
       NAOVTD 15
          (Negotiate About Output Vertcial Tab Disposition)

    2. Command meanings
       In the following, we are discussing a simplex connection, as
       described in the NAOL and NAOP Telnet Options specifications.
          IAC DO NAOVTD
             The data sender requests or agrees to negotiate about output
             vertical tab character disposition with the data receiver.
             In the case where agreement has been reached and in the
             absence of further subnegotiations, the data receiver is
             assumed to be handling output vertical tab character considerations.
          IAC DON'T NAOVTD
             The data sender refuses to negotiate about output vertical tab
             character disposition with the data receiver, or demands a
             return to the unnegotiated default mode.
          IAC WILL NAOVTD
             The data receiver requests or agrees to negotiate about output
             vertical tab character disposition with the sender.  In the
             case where agreement has been reached and in the absence of further
             subnegotiations, the data receiver alone is assumed to be
             handling output vertical tab character considerations.
          IAC WON'T NAOVTD
             The data receiver refuses to negotiate about output vertical
             tab character disposition, or demands a return to the unnegotiated
             default mode.
          IAC SB NAOVTD DS <8-bit value> IAC SE
             The data sender specifies, with the 8-bit value, which party
             should handle output vertical tab characters and what their
             disposition should be.  The code for DS is 1.
          IAC SB NAOVTD DR <8-bit value> IAC SE
             The data receiver specifies, with the 8-bit value, which party
             should handle output vertical tab characters and what their
             disposition should be.  The code for DR is 0.

    3. Default
       DON'T NAOVTD/WON'T NAOVTD
          In the default absence of negotiations concerning which party,
          data sender or data receiver, is handling output vertical tab character
          considerations, neither party is required to handle vertical tab
          characters and neither party is prohibited from handling them; but
          it is appropriate if at least the data receiver handles vertical tab
          character considerations, albeit primitively.

    4. Motivation for the Option
       Please refer to section 4 of the NAOL and of the NAOVTD Telnet option
       descriptions.

    5. Description of the Option
       The data sender and the data receiver use the 8-bit value along with
       the DS and DR SB commands as follows:

          8 bit value   Meaning

          0             Command sender suggests that he alone will handle
                        vertical tab characters, for the connection.
          1 to 250      Command sender suggests that the other party alone
                        should handle tab characters, but suggests that a
                        delay of the indicated value be used. The value is
                        the number of character-times to wait or number of
                        NULs to insert in the data stream before sending the
                        next data character.
          251           Command sender suggests that the other party alone
                        handle vertical tabs, but suggests that each
                        occurrence of the character be replaced by
                        carriage-return/linefeed.
          252           Command sender suggests that the other party alone
                        handle vertical tabs, but suggests that they be discarded.
          253           Command sender suggests that the other party alone
                        should handle tab characters, but suggests that
                        tabbing be simulated.
          254           Command sender suggests that the other party alone
                        should handle the output disposition but suggests
                        waiting for a character to be transmitted (on the
                        other simplex connection) before sending more data.
                        Note that, due to the assynchrony of the two
                        simplex connections, phase problems can occur with
                        this option.
          255           Command sender suggests that the other party alone
                        should handle the output disposition and suggests
                        nothing about how it should be done.

       The guiding rules are that:

          1. if neither data receiver nor data sender wants to handle the
          output vertical tab characters, the data receiver must do it, and
          2. if both data receiver and data sender want to handle the output
          vertical tab characters, the data sender gets to do it.

       The reasoning for the former rule is that if neither want to do it, then
       the default in the NAOVTD option dominates.  If both want to do it, the
       sender, who is presumed to have special knowledge about the data, should
       be allowed to do it, taking into account any suggestions the receiver may
       make.  Simulation is defined as the replacement of the character by
       enough line-feeds (only) to advance the paper (or line-pointer) to the
       next vertical tab stop.
       Note that delays, controlled by the data sender, must consist of NUL
       characters, inserted immediately after the line-feed character.  This is
       necessary due to the assynchrony of network transmissions.  As with all
       option negotiations, neither party should suggest a state already in
       effect except to refuse to negotiate; changes should be acknowledged; and
       once refused, an option should not be resuggested until "something
       changes" (e.g., another process starts).  At any time, either party can
       disable further negotiation by giving the appropriate WON'T NAOVTD or
       DON'T NAOVTD command.