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RFC 0749

Proposed STD
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Telnet SUPDUP-Output option


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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.


2.  Command meanings.


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


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


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


   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.


   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.



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

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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

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

   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

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   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:


   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.

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   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

   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

   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.


   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.