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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.
Mark Crispin [page 1]
NWG/RFC# 736 MRC 31-OCT-77 23:28 42213
Telnet SUPDUP Option
4. Motivation for the option.
Since the publication of RFC 734, 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 RFC 734.
Mark Crispin [page 2]