Telnet SUPDUP-Output option(1)

　　NWG/RFC749 BSG 26-Sep-78 13:13 45499

　　Network Working Group Bernard Greenberg

　　Request for Comments 749 MIT-Multics

　　NIC 45499 18 September 1978

　　TelnetSUPDUP-OUTPUT Option

　　1. Command name and code.

　　SUPDUP-OUTPUT 22

　　2. Command meanings.

　　IAC WILL SUPDUP-OUTPUT

　　The sender of this command REQUESTS permission to transmit　SUPDUP-OUTPUT format messages over the TELNET connection.

　　IAC WON'T SUPDUP-OUTPUT

　　The sender of this command STATES that he will no longer send　SUPDUP-OUTPUT format messages over the TELNET connection.

　　IAC DO SUPDUP-OUTPUT

　　The sender of this command grants the receiver permission to send　SUPDUP-OUTPUT format messages over the TELNET connection.

　　IAC DON'T SUPDUP-OUTPUT

　　The sender of this command DEMANDS that the receiver not send　SUPDUP-OUTPUT format messages over the TELNET connection.

　　IAC SB SUPDUP-OUTPUT 1 IAC SE

　　The sender of this command (which must be the TELNET user process) is　supplying information describing the capabilities of the user　process' terminal.

　　IAC SB SUPDUP-OUTPUT 2 n TD1 TD2 .. TDn SCx SCy IAC SE

　　The sender of this command, which must be the TELNET server process,　is sending explicit screen control information to be carried out by　the user TELNET process.

　　3. Default.

　　WON'T SUPDUP-OUTPUT

　　DON'T SUPDUP-OUTPUT

　　i.e., the SUPDUP-OUTPUT format messages may not be transmitted.

　　4. Motivation for the option.

　　The SUPDUP-OUTPUT protocol provides a means to accessthe virtual　display support provided by the SUPDUP protocol (see RFC734) within　the context of a standard TELNET connection. This allows occasional　display-oriented programs at non-display-oriented servers to take　advantage of the standardized display support provided by SUPDUP.

　　This cannot be done with the standard SUPDUP protocol or the TELNET　SUPDUP option (RFC736), for they both require that all communication　after the negotiation to use SUPDUP has been completed proceed　according to the protocol of RFC734. This places upon the server　total responsibility for screen management for the duration of the　connection, which, by hypothesis, the non-display oriented server is　not willing to accept.

　　User TELNET programs at display-oriented user hosts provide local　screen management by mapping the NVT commands of TELNET into local　screen management commands; often, this involves scrolling,　end-of-page processing, line clearing etc. The SUPDUP-OUTPUT option　allows a display-oriented application program at the server side to　take over screen management explicitly, via the SUPDUP display　control repertoire. TELNET remains in effect throughout. The IAC IP　and other TELNET commands are still valid.

　　By means of the SUPDUP-OUTPUT option, display-oriented programs can　run on the server host, and control the user host's screen　explicitly. The user TELNET process sends a description of the user　terminal (as specified in RFC734) to the server TELNET process as a　subnegiotiation block when the SUPDUP-OUTPUT negotiation has been　successfully completed. The server TELNET process sends explicit　screen control commands via subnegotiation blocks to the user TELNET　process.

　　5. Description of the option.

　　The SUPDUP-OUTPUT protocol may only be initiated by the server TELNET　process. A server TELNET process wishing to take advantage of the　SUPDUP-OUTPUT protocol will initiate a negotiation for it by sending　IAC WILL SUPDUP-OUTPUT. The user TELNET process must accept or　refuse the offer by sending IAC DO SUPDUP-OUTPUT or IAC DON'T　SUPDUP-OUTPUT.