RFC 656 (rfc656) - Page 1 of 1

Telnet output vertical tabstops option

TELNET OUTPUT VERTICAL TABSTOPS OPTION
RFC 656, NIC 31159 (Oct. 25, 1974)"
D. Crocker (UCLA-NMC)
Online file: [ISI]NAOVTS.TXT

                TELNET OUTPUT VERTICAL TABSTOPS OPTION

1. Command name and code
   NAOVTS 14
      (Negotiate About Vertcial Tabstops)

2. Command meanings
   In the following, we are discussing a simplex connection, as described in 
   the NAOL and NAOP Telnet Options specifications.
      IAC DO NAOVTS 
         The data sender requests or agrees to negotiate about output
         vertical tabstops 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 tabstop considerations.
      IAC DON'T NAOVTS 
         The data sender refuses to negotiate about output vertical tabstops 
         with the data receiver, or demands a return to the unnegotiated 
         default mode.
      IAC WILL NAOVTS 
         The data receiver requests or agrees to negotiate about output 
         vertical tabstops 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 tabstop 
         considerations.
      IAC WON'T NAOVTS 
         The data receiver refuses to negotiate about output vertical
         tabstops, or demands a return to the unnegotiated default mode.
      IAC SB NAOVTS DS  ...  IAC SE
         The data sender specifies, with the 8-bit value(s), which party
         should handle output vertical tabstop considerations and what the
         stops should be.  The code for DS is 1.
      IAC SB NAOVTS DR  ...  IAC SE
         The data receiver specifies, with the 8-bit value(s), which party 
         should handle output vertical tabstop considerations and what the 
         stops should be.  The code for DR is 0.

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

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

5. Description of the Option
   The data sender and the data receiver use the 8-bit value(s) along with
   the DS and DR SB commands as follows (multiple 8-bit values are allowed
   only if each is greater than zero and less than 251):

      8-bit value                      Meaning                      

      0            Command sender suggests that he alone will handle  
                   the vertical tabstops, for the connection.         
      1 to 250     Command sender suggests that the other party alone 
                   should handle the stops, but suggests that the     
                   indicated value(s) be used.  Each value is the line 
                   number, relative to the top of the printer page or 
                   terminal screen, that is to be set as a vertical   
                   tabstop.                                           
      251 to 254   Not allowed, in order to be compatible with        
                   related Telnet options.                            
      255          Command sender suggests that the other party alone 
                   should handle output vertical tabstops 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 output 
      vertical tabstops, the data receiver must do it, and
      2) if both data receiver and data sender want to handle output vertical 
      tabstops, the data sender gets to do it.

The reasoning for the former rule is that if neither wants to do it, then 
the default in the NAOVTS 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.
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 NAOVTS or DON'T NAOVTS command.