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TELNET OUTPUT HORIZONTAL TAB DISPOSITION OPTION RFC 654, NIC 31157 (Oct. 25, 1974) D. Crocker (UCLA-NMC) Online file: [ISI]<DCROCKER>NAOHTD.TXT

         TELNET OUTPUT HORIZONTAL TAB DISPOSITION OPTION

1. Command name and code

 NAOHTD 12
    (Negotiate About Output Horizontal Tab Disposition)

2. Command meanings

 In the following, we are discussing a simplex connection, as described in 
 the NAOL and NAOP Telnet options.
    IAC DO NAOHTD
       The data sender requests or agrees to negotiate about output 
       horizontal 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 
       horizontal tab character considerations.
    IAC DON'T NAOHTD
       The data sender refuses to negotiate about output horizontal tab 
       characters with the data receiver, or demands a return to the 
       unnegotiated default mode.
    IAC WILL NAOHTD
       The data receiver requests or agrees to negotiate about output
       horizontal tab characters 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 horizontal tab character considerations.
    IAC WON'T NAOHTD
       The data receiver refuses to negotiate about output horizontal tab 
       characters, or demands a return to the unnegotiated default mode. 
    IAC SB NAOHTD DS <8-bit value> IAC SE
       The data sender specifies, with the 8-bit value, which party should
       handle output horizontal tab characters and what their disposition
       should be.  The code for DS is 1.
    IAC SB NAOHTD DR <8-bit value> IAC SE
       The data receiver specifies, with the 8-bit value, which party
       should handle output horizontal tab characters and what their
       disposition should be.  The code for DR is 0.

3. Default

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

4. Motivation for the Option

 Please refer to section 4 of the NAOL and of the NAOP 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  
                 horizontal tab characters, for the connection.     
    1 to 250     Command sender suggests that the other party alone 
                 should handle horizontal 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 horizontal tabs, but suggests that each     
                 occurrence of the character be replaced by a space. 
    252          Command sender suggests that the other party alone 
                 handle horizontal tabs, but suggests that they be  
                 discarded.                                         
    253          Command sender suggests that the other party alone 
                 should handle horizontal tab characters, but       
                 suggests that tabbing be simulated.                
    254          Command sender suggests that the other party alone 
                 should handle horizontal tab characters, but       
                 suggests that 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 output horizontal tabs 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 
    horizontal tab characters, the data receiver must do it, and
    2) if both data receiver and data sender wants to handle output 
    horizontal tab characters, 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 NAOHTD 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 horizontal tab
 character by enough spaces to move the printer head (or line-pointer) to
 the next horizontal tab stop.
 Note that delays, controlled by the data sender, must consist of NUL
 characters inserted immediately after the horizontal tab 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 NAOHTD or
 DON'T NAOHTD command.