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.
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.
