Request for Comments: 698 Jul 1975
TELNET EXTENDED ASCII OPTION
1. Command Name and Code.
2. Command Meanings.
IAC WILL EXTEND-ASCII
The sender of this command requests Permission to begin
transmitting, or confirms that it may now begin transmitting extended ASCII, where additional 'control' bits are added to
normal ASCII, which are treated sPecially by certain programs on
the host computer.
IAC WON'T EXTEND-ASCII
If the connection is already being operated in extended ASCII
mode, the sender of this command demands that the receiver begin transmitting data characters in standard NVT ASCII. If the
connection is not already being operated in extended ASCII mode, The sender of this command refuses to begin transmitting extended
IAC DO EXTEND-ASCII
The sender of this command requests that the receiver begin
transmitting,or confirms that the receiver of this command is
allowed to begin transmitting extended ASCII.
IAC DON'T EXTEND-ASCII
The sender of this command demands that the receiver of this
command stop or not start transmitting data in extended ASCII
IAC SB EXTASC
<high order bits (bits 15-8)><low order bits (bits 7-0)> IAC SE
This command transmits an extended ASCII character in the form of
two 8-bit bytes. Each 8-bit byte contains 8 data bits.
i.e., only use standard NVT ASCII
Several sites on the net, for example, SU-AI and MIT-AI, use
keyboards which use almost all 128 characters as printable
characters, and use one or more additional bits as "control' bits as command modifiers or to separate textual input from command input to programs. Without these additional bits, several characters cannot be entered as text because they are used for control purposes, such
as the greek letter "beta' which on a TELNET connection is CONTROL-C and is used for stopping ones job. In addition there are several commonly used programs at these sites which require these additional bits to be run effectively. Hence it is necessary to provide some
means of sending characters larger than 8 bits wide.
5. Description of the option.
This option is to allow the transmission of extended ASCII.
Experience has shown that most of the time, 7-bit ASCII is typed,
with an occasional "control' character used. Hence, it is expected normal NVT ASCII would be used for 7-bit ASCII and that
extended-ASCII be sent as an escape character sequence.
The exact meaning of these additional bits depends on the user
program. At SU-AI and at MIT-AI, the first two bits beyond the normal 7-bit ASCII are passed on to the user program and are denoted as follows.
Bit 8 (or 200 octal) is the CONTROL bit
Bit 9 (or 400 octal) is the META bit
(NOTE: "CONTROL' is used in a non-standard way here; that is, it
usually refers to codes 0-37 in NVT ASCII. CONTROL and META are
echoed by prefixing the normal character with 013 (integral symbol) for CONTROL and 014 (plus-minus) for META. If both are present, it is known as CONTROL-META and echoed as 013 014 7-bit character.)
6. Description of Stanford Extended ASCII Characters
In this section, the extended graphic character set used at SU-AI is
described for reference, although this specific character set is not
required as part of the extended ASCII Telnet option. Characters
described as "hidden" are alternate graphic interpretations of codes
normally used as format effectors, used by certain typesetting
Code Graphic represented
000 null (hidden vertically centered dot)
001 downward arrow
002 alpha (all Greek letters are lowercase)
004 logical and (caret)
005 logical not (dash with downward extension)
011 tab (hidden gamma)
012 linefeed (hidden delta)
013 vertical tab (hidden integral)
014 formfeed (hidden plus-minus)
015 carriage return (hidden circled-plus)
017 del (partial differential)
020 proper subset (right-opening horseshoe)
021 proper superset (left-opening horseshoe)
022 intersection (down-opening horseshoe)
023 union (up-opening horseshoe)
024 universal quantifier (upside-down A)
025 existential quantifier (backwards E)
027 left-right double headed arrow
031 right pointing arrow
036 equivalence (column of 3 horizontal bars)
037 logical or (V shape)
040-135 as in standard ASCII
136 upward pointing arrow
137 left pointing arrow
140-174 as in standard ASCII
175 altmode (prints as lozenge)
176 right brace
177 rubout (hidden circumflex)