Telnet extended ASCII option

　　Request for Comments: 698 Jul 1975

　　NIC #32964

　　TELNETEXTENDED ASCII OPTION

　　1. Command Name and Code.

　　EXTEND-ASCII 17

　　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　ASCII.

　　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　mode.

　　IAC SB EXTASC

　　 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.

　　-1-

　　TELNET EXTENDED ASCII OPTION　RFC698, NIC 32964 (July 23 1975)

　　3. Default

　　DON'T EXTEND-ASCII

　　WON'T EXTEND-ASCII

　　i.e., only use standard NVT ASCII

　　4. Motivation.

　　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.)

　　-2-

　　TELNET EXTENDED ASCII OPTION

　　RFC698, NIC 32964 (July 23, 1975)

　　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　programs.

　　Code Graphic represented

　　000 null (hidden vertically centered dot)

　　001 downward arrow

　　002 alpha (all Greek letters are lowercase)

　　003 beta

　　004 logical and (caret)

　　005 logical not (dash with downward extension)

　　006 epsilon

　　007 pi

　　010 lambda

　　011 tab (hidden gamma)

　　012 linefeed (hidden delta)

　　013 vertical tab (hidden integral)

　　014 formfeed (hidden plus-minus)

　　015 carriage return (hidden circled-plus)

　　016 infinity

　　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)

　　026 circled-times

　　027 left-right double headed arrow

　　030 underbar

　　031 right pointing arrow

　　032 tilde

　　033 not-equal

　　034 less-than-or-equal

　　035 greater-than-or-equal

　　036 equivalence (column of 3 horizontal bars)

　　037 logical or (V shape)

　　040-135 as in standard ASCII

　　-3-

　　TELNET EXTENDED ASCII OPTION

　　RFC698, NIC 32964 (July 23, 1975)

　　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)