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.

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.