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+Network Working Group                                          B. Miller
+Request for Comments: 1097                                    CMU-NetDev
+                                                            1 April 1989
+
+                    TELNET SUBLIMINAL-MESSAGE Option
+
+Status of this Memo
+
+   This RFC specifies a standard for the Internet community.  Hosts on
+   the Internet that display subliminal messages within the Telnet
+   protocol are expected to adopt and implement this standard.
+   Distribution of this memo is unlimited.
+
+1.  Command name and code.
+
+   SUBLIMINAL-MESSAGE        257
+
+2.  Command meanings.
+
+   IAC WILL SUBLIMINAL-MESSAGE
+
+      The sender of this command REQUESTS permission to, or confirms
+      that it will, display subliminal messages.
+
+   IAC WONT SUBLIMINAL-MESSAGE
+
+      The sender of this command REFUSES to display subliminal messages.
+
+   IAC DO SUBLIMINAL-MESSAGE
+
+      The sender of this command REQUESTS that the receiver, or grants
+      the receiver permission to, display subliminal messages.
+
+   IAC DONT SUBLIMINAL-MESSAGE
+
+      The sender of this command DEMANDS that the receiver not display
+      subliminal messages.
+
+   IAC SB SUBLIMINAL-MESSAGE <16-bit value> <16-bit value> <string> IAC
+      SE
+
+      The sender specifies a message to be subliminaly displayed by the
+      remote host.  If the client has agreed (via the standard WILL WONT
+      DO DONT mechanism) to display subliminal messages, it must accept
+      this subnegotiation and attempt to display the message string on
+      the users console for the specified duration and continue to do so
+      at fixed intervals until another SUBLIMINAL-MESSAGE subnegotiation
+      is received.  The position and rendering of the message of
+
+
+
+Miller                                                          [Page 1]
+
+RFC 1097                       SUBLIMINAL                   1 April 1989
+
+
+      implementation dependent.
+
+      The first 16-bit value specifies the duration of the message in
+      milliseconds.  It is sent MSB first.  The second 16-bit value
+      specifies the frequency with which the message is displayed.  It
+      represents the number of seconds between displays and is also sent
+      MSB first.  The final parameter is the message itself.
+
+      The syntax for this subnegotiation is:
+
+                IAC SB SUBLIMINAL-MESSAGE
+                    DURATION[1] DURATION[0]
+                    FREQUENCY[1] FREQUENCY[0]
+                    MESSAGE_STRING
+                IAC SE
+
+      As required by the Telnet protocol, any occurence of 255 in the
+      subnegotiation must be doubled to destinguish it from the IAC
+      character (which has a value of 255).
+
+3.  Default.
+
+   WONT SUBLIMINAL-MESSAGE
+
+   DONT SUBLIMINAL-MESSAGE
+
+   i.e., subliminal messages will not be displayed.
+
+4.  Motivation for the option
+
+   Frequently the use of "Message of the day" banners and newsletters is
+   insufficient to convince stubborn users to upgrade to the latest
+   version of telnet.  Some users will use the same outdated version for
+   years.  I ran across this problem trying to convince people to use
+   the REMOTE-FLOW-CONTROL Telnet option.  These users need to be gently
+   "persuaded".
+
+5.  Description and implementation notes.
+
+   The quality of the client implementation will depend on it's ability
+   to display and erase text strings in a small amount of time.  The
+   current implementation at CMU takes into acount terminal line speed,
+   advanced video capabilities, and screen phospher persistance when
+   calculating how long to wait before erasing a message.
+
+   While it is permitted for the client to display the message text
+   "in-line", best results at obtained by printing the message at the
+   top or side of console screen where it will just catch the corner of
+
+
+
+Miller                                                          [Page 2]
+
+RFC 1097                       SUBLIMINAL                   1 April 1989
+
+
+   the user's visual field.
+
+   A version is currently under development at CMU to display the
+   message using morse-code over the keyboard caps-lock LED.
+
+6.  Examples
+
+   In the following example all numbers are in decimal notation.
+
+   1.  Server suggests and client agrees to use SUBLIMINAL-MESSAGE.
+
+      (Server sends) IAC DO SUBLIMINAL-MESSAGE
+      (Client sends) IAC WILL SUBLIMINAL-MESSAGE
+      (Server sends) IAC SB SUBLIMINAL-MESSAGE 0 5 0 20 "Use VMS" IAC SE
+
+         [The server is "suggesting" that the user employ a stable
+         operating system, not an unreasonable request...]
+
+      The client should immediately begin displaying the message and
+      should continue to do so at regular intervals.
+
+   2.  Server preempts previous subliminal message.
+
+      (Server sends) IAC SB SUBLIMINAL-MESSAGE 0 5 0 20 "Go home" IAC SE
+
+      The client should now no longer display the previous message and
+      should immediately begin displaying the new one.
+
+   3.  Server has messed with user enough for one day.
+
+      (Server sends) IAC SB SUBLIMINAL-MESSAGE 0 0 0 0 "" IAC SE
+
+      The client must cease display of any subliminal messages.
+
+7.  Acknowledgements.
+
+   We do things just a little sneakier here at CMU.
+
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+Miller                                                          [Page 3]
+
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