Telnet Timing Mark Option(1)

　　Network Working Group J. Postel

　　Request for Comments: 860 J. Reynolds

　　ISI

　　Obsoletes: NIC 16238 May 1983

　　TELNETTIMING MARK OPTION

　　This RFCspecifies a standard for the ARPA community. Hosts on the ARPA　Internet are expected to adopt and implement this standard.

　　1. Command Name and Code

　　TIMING-MARK 6

　　2. Command Meanings

　　IAC DO TIMING-MARK

　　The sender of this command REQUESTS that the receiver of this　command return a WILL TIMING-MARK in the data stream at the　"appropriate place" as defined in section 4 below.

　　IAC WILL TIMING-MARK

　　The sender of this command ASSURES the receiver of this command　that it is inserted in the data stream at the "appropriate place"　to insure synchronization with a DO TIMING-MARK transmitted by the　receiver of this command.

　　IAC WON'T TIMING-MARK

　　The sender of this command REFUSES to insure that this command is　inserted in the data stream at the "appropriate place" to insure　synchronization.

　　IAC DON'T TIMING-MARK

　　The sender of this command notifies the receiver of this command　that a WILL TIMING-MARK (previously transmitted by the receiver of　this command) has been IGNORED.

　　3. Default

　　WON'T TIMING-MARK, DON'T TIMING-MARK

　　i.e., No explicit attempt is made to synchronize the activities at　the two ends of the TELNET connection.

　　4. Motivation for the Option

　　RFC860May 1983

　　It is sometimes useful for a user or process at one end of a TELNET　connection to be sure that previously transmitted data has been　completely processed, printed, discarded, or otherwise disposed of.

　　This option provides a mechanism for doing this. In addition, even　if the option request (DO TIMING-MARK) is refused (by WON'T　TIMING-MARK) the requester is at least assured that the refuser has　received (if not processed) all previous data.

　　As an example of a particular application, imagine a TELNET　connection between a physically full duplex terminal and a "full　duplex" server system which permits the user to "type ahead" while　the server is processing previous user input. Suppose that both　sides have agreed to Suppress Go Ahead and that the server has agreed　to provide echoes. The server now discovers a command which it　cannot parse, perhaps because of a user typing error. It would like　to throw away all of the user's "type-ahead" (since failure of the　parsing of one command is likely to lead to incorrect results if　subsequent commands are executed), send the user an error message,　and resume interpretation of commands which the user typed after　seeing the error message. If the user were local, the system would　be able to discard the buffered input; but input may be buffered in　the user's host or elsewhere. Therefore, the server might send a DO　TIMING-MARK and hope to receive a WILL TIMING-MARK from the user at　the "appropriate place" in the data stream.

　　The "appropriate place", therefore (in absence of other information)　is clearly just before the first character which the user typed after　seeing the error message. That is, it should appear that the timing　mark was "printed" on the user's terminal and that, in response, the　user typed an answering timing mark.

　　Next, suppose that the user in the example above realized that he had　misspelled a command, realized that the server would send a DO　TIMING-MARK, and wanted to start "typing ahead" again without waiting　for this to occur. He might then instruct his own system to send a　WILL TIMING-MARK to the server and then begin "typing ahead" again.