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]