Telnet Protocols(2)

　　TELNET CONTROL SIGNALS

　　NAME CODE MEANING

　　DATA MARK 128 Used to mark a point in the data stream.

　　Used in conjunction with INS. See SYNCH.

　　BREAK 129 User-to-Server: Has the same meaning to　the server as the "Break," "Interrupt," or　"Attention" button found on many terminals.

　　Server-to-User: Has the same meaning to　to use as the "reverse break" used with　some terminals.

　　NOP 130 No Operation.

　　NO ECHO 131 User-to-Server: Asks the server not to　return Echos of the transmitted data.

　　Server-to-User: States that the server is　not sending echos of the transmitted data.　　

      Sent only as a reply to ECHO or NO ECHO,　or to end the hide your input.

　　ECHO 132 User-to-Server: Asks the server to send　Echos of the transmitted data.

　　Server-to User: States that the server is　sending echos of the transmitted data.

　　Sent only as a reply to ECHO or NO ECHO.

　　Hide your input 133 The intention is that a server will send　this signal to a user system which is　echoing locally (to the user) when the user　is about to type something secret (e.g. a　password). In this case, the user system　is to suppress local echoing or overprint　the input (or something) until the server　sends a NOECHO signal. In situations where　the user system is not echoing locally,　this signal must not be sent by the server.

　　INS --- This is the "Interrupt on Send" signal,　defined by the Host-to-Host protocol and　implemented by the Network Control Program

　　(NCP). See SYNCH.

　　SYNCH --- This is a condition indicated by the　combination of the DATA MARK and the INS.

　　User-to-Server: The Server is to examine　the input data stream looking for a DATA　MARK signal; if a DATA MARK is found, the　server must not process further until an　INS is received. If the server receives an　INS, it is required to examine the data　stream at once, taking any appropriate　action on "break type" characters (e.g.　etx, sub, BREAK), up to a DATA MARK signal　and thereupon continue its normal processing.

　　The passed over characters may be discarded.

　　Server-to-User: If the user finds a DATA　MARK in the data stream, it must wait for　an INS. If the user receives an INS, it　must examine and discard characters up to　and including a DATA MARK.

　　DATA TYPES

　　Telnet normally deals in ASCII characters, but there are provisions　for escaping to other code sets. If one of these escapes is used, it　is undefined (here) whether or not the Telnet signals still have　meaning or even how to return to the ASCII set: The Telnet signals　used to indicate a change of code set are:

　　CODE MEANING

　　160 ASCII - Standard Telnet

　　161 Transparent

　　162 EBCDIC

　　USER TELNET SIGNALS

　　The following signals are to be available to the human user to cause　the user Telnet to take the indicated action.

　　Transmit Now - Transmit all data entered and locally　buffered now. Intended to be used with line　mode.

　　Suppress end-of-line - Transmit all data entered and locally　buffered now, and do not transmit the　end-of-line immediately following this signal.

　　STANDARD TELNET IMPLEMENTATION

　　Using Site

　　1) User is able to enter and transmit all ASCII codes

　　2) User is able to cause the Telnet signals BREAK, SYNCH, ECHO and　NOECHO to be transmitted.

　　3) Provides for the User Telnet signals, (e.g. Transmit Now).

　　4) Implements the CR LF end-of-line convention.

　　5) Provides local echo for local user terminals.

　　6) Correctly processes the Telnet signals BREAK, SYNCH, NOP, ECHO,　NOECHO, and Hide Your Input received from the server.

　　Serving Site:

　　1) Provides a mapping between ASCII and the local character set.

　　2) Correctly processes the Telnet signals BREAK, SYNCH, NOP, NOECHO,　and ECHO.

　　3) Implements the CR LF end-of-line convention.

　　4) Assumes the using site provides echoing. May provide a server　echo mode.

　　MINIMUM TELNET IMPLEMENTATION

　　Using Site:

　　1) User must be able to enter and transmit all ASCII codes.

　　2) Ignore and delete all Telnet signals from the serving site.

　　3) Provide local echo for local user terminals.

　　4) Implements CR LF end-of-line convention.

　　5) Provide for the User Telnet signals.

　　Serving Site:

　　1) Provide a mapping between ASCII and the local character set.

　　2) Ignore and Delete all Telnet signals from the using site.

　　3) Assume the using site provides echoing.

　　4) Implements the CR LF end-of-line convention.

　　III. DISCUSSION OF TELNET PROTOCOL