Telnet output vertical tab disposition option

　　D. Crocker (UCLA-NMC)

　　RFC657, NIC 31160 (Oct. 25, 1974)

　　Online file: [ISI]NAOVTD.TXT

　　TELNETOUTPUT 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.