Telnet output horizontal tab disposition option
RFC 654

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.