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