    NWG/RFC  749                                  BSG 26-Sep-78 13:13  45499
    Network Working Group                                  Bernard Greenberg
    Request for Comments 749                                     MIT-Multics
    NIC 45499                                              18 September 1978

                          Telnet SUPDUP-OUTPUT Option

    1.  Command name and code.

       SUPDUP-OUTPUT   22

    2.  Command meanings.

       IAC WILL SUPDUP-OUTPUT

       The  sender   of  this  command   REQUESTS   permission  to  transmit
       SUPDUP-OUTPUT format messages over the TELNET connection.

       IAC WON'T SUPDUP-OUTPUT

       The sender  of this command  STATES  that  he  will  no  longer  send
       SUPDUP-OUTPUT format messages over the TELNET connection.

       IAC DO SUPDUP-OUTPUT

       The sender  of this command  grants  the receiver  permission to send
       SUPDUP-OUTPUT format messages over the TELNET connection.

       IAC DON'T SUPDUP-OUTPUT

       The sender  of this  command  DEMANDS  that  the  receiver  not  send
       SUPDUP-OUTPUT format messages over the TELNET connection.

       IAC SB SUPDUP-OUTPUT 1 <terminal-parameters> IAC SE

       The sender of this command (which must be the TELNET user process) is
       supplying   information  describing  the  capabilities  of  the  user
       process' terminal.

       IAC SB SUPDUP-OUTPUT 2 n TD1 TD2 ..  TDn SCx SCy IAC SE

       The sender  of this command, which must be the TELNET server process,
       is sending  explicit  screen control information to be carried out by
       the user TELNET process.

    3.  Default.

       WON'T SUPDUP-OUTPUT

       DON'T SUPDUP-OUTPUT

       i.e., the SUPDUP-OUTPUT format messages may not be transmitted.

    Greenberg                                                       [page 1]

    NWG/RFC  749                                  BSG 26-Sep-78 13:13  45499
    Telnet SUPDUP-OUTPUT Option

    4.  Motivation for the option.

       The SUPDUP-OUTPUT  protocol  provides  a means to access  the virtual
       display  support provided by the SUPDUP protocol (see RFC 734) within
       the context  of a standard  TELNET connection. This allows occasional
       display-oriented  programs  at non-display-oriented  servers  to take
       advantage  of the standardized  display  support  provided by SUPDUP.
       This cannot  be done with the standard  SUPDUP protocol or the TELNET
       SUPDUP option (RFC 736), for they both require that all communication
       after the negotiation  to  use  SUPDUP  has  been  completed  proceed
       according  to the protocol  of RFC 734.   This places upon the server
       total responsibility  for screen  management  for the duration of the
       connection,  which, by hypothesis, the non-display oriented server is
       not willing to accept.

       User TELNET  programs  at display-oriented  user hosts provide  local
       screen  management  by mapping  the NVT commands of TELNET into local
       screen   management   commands;   often,   this  involves  scrolling,
       end-of-page  processing, line clearing etc.  The SUPDUP-OUTPUT option
       allows  a display-oriented  application program at the server side to
       take over  screen  management  explicitly,  via  the  SUPDUP  display
       control repertoire.  TELNET remains in effect throughout.  The IAC IP
       and other TELNET commands are still valid.

       By means of the SUPDUP-OUTPUT  option,  display-oriented programs can
       run  on  the  server   host,  and  control  the  user  host's  screen
       explicitly.   The user TELNET process sends a description of the user
       terminal  (as specified in RFC 734) to the server TELNET process as a
       subnegiotiation  block when the SUPDUP-OUTPUT  negotiation  has  been
       successfully  completed.   The server  TELNET  process sends explicit
       screen  control commands via subnegotiation blocks to the user TELNET
       process.

    5.  Description of the option.

       The SUPDUP-OUTPUT protocol may only be initiated by the server TELNET
       process.   A server  TELNET  process wishing to take advantage of the
       SUPDUP-OUTPUT  protocol will initiate a negotiation for it by sending
       IAC WILL SUPDUP-OUTPUT.   The user  TELNET  process  must  accept  or
       refuse  the offer by  sending  IAC  DO  SUPDUP-OUTPUT  or  IAC  DON'T
       SUPDUP-OUTPUT.

       If the user  TELNET  process  agrees  to  support  the  SUPDUP-OUTPUT
       option,   it  must  follow   the  sending  of  IAC  DO  SUPDUP-OUTPUT
       immediately   with  a  description  of  the  user's  terminal.   This
       information  is described in RFC 734 as the "terminal parameters." It
       is to be sent as a series  of six-bit  bytes,  one byte per eight-bit

    Greenberg                                                       [page 2]

    NWG/RFC  749                                  BSG 26-Sep-78 13:13  45499
    Telnet SUPDUP-OUTPUT Option

       TELNET  data byte.   These  words may or may not contain the optional
       line speed and graphics capabilities parameters described by RFC 747;
       the first  six bytes  specify  the count of 36-bit words to follow as
       described by RFC 734.

       The terminal  parameter block will be sent as a subnegotiation of the
       SUPDUP-OUTPUT option:

       IAC SB SUPDUP-OUTPUT 1 byte1 byte2 ... byten IAC SE

       The byte of "1"  is a command  code,  for compatibility  with  future
       extensions.   Upon receipt  of the terminal  parameter block from the
       user TELNET process, the server TELNET process may send SUPDUP-OUTPUT
       blocks as described below.

       The server  TELNET  process  can specify explicit control of the user
       host's  screen  by  the  sending  of  subnegotiation  blocks  of  the
       SUPDUP-OUTPUT  option.   The format  of such  a  block,  as  seen  in
       eight-bit TELNET data bytes, is:

       IAC SB SUPDUP-OUTPUT 2 N TD1 TD2 TD3 ... TDn SCx SCy IAC SE

       The byte of "2"  is a command  code,  for compatibility  with  future
       extensions.  The TDm bytes are the "%TDCODEs" and printing characters
       of SUPDUP  output  of RFC 734.  N is a byte containing a count of the
       number  of TDm's in this transmission.  N may be zero, and may not be
       greater than 254 (decimal).  SCx and SCy are two bytes specifying the
       anticipated horizontal and vertical (respectively) coordinates of the
       cursor of the user host's screen after the latter has interpreted all
       the %TDCODEs in this transmission.

       The motivation  for the SCx SCy screen  position  specification is to
       allow hosts running the ITS operating system, which will transmit the
       TDCODEs  directly  into the local output  system, to assert the "main
       program  level"  screen  position  without  any interpretation of the
       transmitted TDCODE sequence by the user TELNET program.

       The user TELNET  process must manage the position of the local cursor
       with respect  to standard  TELNET NVT commands and output, and SUPDUP
       OUTPUT  transmissions.   The user TELNET  process may assume that the
       server  TELNET  process is managing both NVT and SUPDUP-OUTPUT output
       in an integrated way.

       The SUPDUP-OUTPUT  option makes no statement about how input is sent;
       this may be negotiated via other options.  By default, NVT input will
       be used.   The user-to-server  screen  management commands of RFC 734
       are NOT implicitly handled by IAC WILL SUPDUP-OUTPUT.

    Greenberg                                                       [page 3]

    NWG/RFC  749                                  BSG 26-Sep-78 13:13  45499
    Telnet SUPDUP-OUTPUT Option

       In the absence  of the transmission  of SUPDUP-OUTPUT  subnegotiation
       blocks,  a TELNET  connection operating with the SUPDUP-OUTPUT option
       in effect is indistinguishable from a normal TELNET connection.  Thus
       IAC WON'T SUPDUP-OUTPUT  is highly  optional,  and if received by the
       user TELNET  process,  should  only be used to cause  a diagnostic if
       SUPDUP-OUTPUT  subnegotiation  blocks  are subsequently received.  If
       received,  the user TELNET  process  should  respond  with IAC  DON'T
       SUPDUP OUTPUT.

       Because  of the optional  nature of IAC WON'T SUPDUP-OUTPUT, the user
       TELNET  process  should  be prepared  to send the terminal  parameter
       subnegotiation  block each time IAC WILL SUPDUP-OUTPUT  is  received,
       i.e., even if the user TELNET process believes SUPDUP-OUTPUT to be in
       effect.

       The %TDORS  (output  reset)  code may not be sent in a  SUPDUP-OUTPUT
       transmission.   The user TELNET  program may assume that no byte in a
       subnegotiation block will be 255 (decimal).

       No multi-byte  TDCODE  sequence  (e.g.,  %TDMOV, %TDILP) may be split
       across SUPDUP-OUTPUT subnegotiation blocks.

    References:

       Crispin, Mark:

          "SUPDUP Display Protocol", RFC 734, 7 October 1977, NIC 44213.

       Crispin, Mark:

          "TELNET SUPDUP Option", RFC 736, 31 October 1977, NIC 44213.

       Crispin, Mark:

          "Recent  Extensions  to the SUPDUP  Protocol",  RFC 747,  21 March
          1978, NIC 44015.

    Greenberg                                                       [page 4]