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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.