Telnet SUPDUP option

　　NWG/RFC# 736 MRC 31-OCT-77 23:28 42213

　　Telnet SUPDUP Option

　　Network Working Group Mark Crispin

　　Request for Comments 736 SU-AI

　　NIC 42213 31 October 1977

　　TELNET SUPDUP Option

　　1. Command name and code.

　　SUPDUP 21

　　2. Command meanings.

　　IAC WILL SUPDUP

　　The sender of this command REQUESTS permission to, or confirms　that it will, use the SUPDUP display protocol

　　IAC WON'T SUPDUP

　　The sender of this command REFUSES to use the SUPDUP protocol.

　　IAC DO SUPDUP

　　The sender of this command REQUESTS that the receiver use, or　grants the receiver permission to use, the SUPDUP protocol.

　　IAC DON'T

　　The sender of this command DEMANDS that the receiver not use the　SUPDUP protocol.

　　3. Default.

　　WON'T SUPDUP

　　DON'T SUPDUP

　　i.e., the SUPDUP display protocol is not in use.

　　NWG/RFC# 736 MRC 31-OCT-77 23:28 42213

　　Telnet SUPDUP Option

　　4. Motivation for the option.

　　Since the publication of RFC734, I have been requested to design　an option to the TELNET protocol to provide for SUPDUP service.

　　This option allows a host to provide SUPDUP service on the normal　TELNET socket (27 octal) instead of 137 (octal) which is the normal　SUPDUP ICP socket.

　　5. Description of the option.

　　A user TELNET program which wishes to use the SUPDUP display　protocol instead of the NVT terminal service should send an IAC DO　SUPDUP. If the server is willing to use the SUPDUP display　protocol, it should respond with IAC WILL SUPDUP; otherwise it　should refuse with IAC WONT SUPDUP.

　　For hosts which normally provide SUPDUP terminal services, the　server can send IAC WILL SUPDUP upon ICP which the user may then　accept or refuse.

　　If the SUPDUP option is in effect, no further TELNET negotiations　are allowed. They are meaningless, since SUPDUP has its own　facilities to perform the functions that are needed. Hence, octal　377 will become an ordinary transmitted character (in this case an　invalid %TD code) instead of an IAC.

　　Following the mutual acceptance of the SUPDUP option, the SUPDUP　negotiation proceeds as described in RFC734.