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Network Working Group                                       S. SilvermanRequest for Comments: 933                               MITRE-Washington                                                            January 1985OUTPUT MARKING TELNET OPTIONStatus of this Memo   This RFC proposes a new option for Telnet for the ARPA-Internet   community, and requests discussion and suggestions for improvements.   Distribution of this memo is unlimited.Overview   This proposed option would allow a Server-Telnet to send a banner to   a User-Telnet so that this banner would be displayed on the   workstation screen independently of the application software running   in the Server-Telnet.1.  Command Name and Code   OUTMRK    272.  Command Meanings   IAC WILL OUTMRK      Sender is willing to send output marking information in a      subsequent sub-negotiation.   IAC WON'T OUTMRK      Sender refuses to send output marking information.   IAC DO OUTMRK      Sender is willing to receive output marking information in a      subsequent sub-negotiation.   IAC DON'T OUTMRK      Sender refuses to accept output marking information.   IAC SB OUTMRK CNTL data IAC SE      The sender requests receiver to use the data in this      subnegotiation as a marking for the normally transmitted Telnet      data until further notice.  The CNTL octet indicates the position      of the marking (see below).Silverman                                                       [Page 1]

RFC 933                                                     January 1985Output Marking Telnet Option   IAC SB OUTMRK ACK IAC SE      The sender acknowledges the data and agrees to use it to perform      output marking (see below).   IAC SB OUTMRK NAK IAC SE      The sender objects to using the data to perform output marking      (see below).3.  Default   WON'T OUTMRK      Output marking information will not be exchanged.   DON'T OUTMRK      Output marking information will not be exchanged.4.  Motivation for the Option   The security architecture of some military systems identifies a   security level with each Telnet connection.  There is a corresponding   need to display a security banner on visual display devices.   (Reference: Department of Defense Trusted Computer System Evaluation   Criteria,Section 3.1.1.3.2.3, Labeling Human-Readable Output.)   The output marking is currently done by transmitting the banner as   data within each screen of data.  It would be more efficient to   transmit the data once with instructions and have User-Telnet   maintain the banner automatically without any additional   Server-Telnet action.  This frees Server-Telnet from needing to know   the output device page size.   Under this proposal Server-Telnet would send an option sequence with   the command, a control flag, and the banner to be used.  While   current systems use the top of the screen, it is conceivable other   systems would want to put the banner at the bottom or perhaps even   the side of the screen.  This is the reason for the control flag.5.  Description of the Option   Either side of the session can initiate the option; however, normally   it will be the server side that initiates the request to perform   output marking.  Either the Server-Telnet sends "WILL OUTMRK" or the   User-Telnet sends a "DO OUTMRK".  The party receiving the initialSilverman                                                       [Page 2]

RFC 933                                                     January 1985Output Marking Telnet Option   "WILL" (or "DO") would respond with "DO" (or "WILL") to accept the   option.  Then Server-Telnet responds with the marking data.  The   format of this is:      "IAC SB OUTMRK CNTL data IAC SE"         CNTL is the Control Flag described below,         the data is in ASCII.   If this is satisfactory, User-Telnet responds:      "IAC SB OUTMRK ACK IAC SE"         ACK is the ASCII ACK (6).   From this point, User-Telnet will have to translate any command which   uses cursor controls so that the application data is mapped to the   application part of the screen.   If the data passed in the subnegotiation field is unacceptable to   User-Telnet, then it responds with:      "IAC SB OUTMRK NAK IAC SE"         NAK is the ASCII NAK (21).   It is now up to Server-Telnet to start the sequence over again and   use "more acceptable" data (or possibly take other action such as   connection termination).   To terminate output marking, Server-Telnet transmits "WON'T OUTMRK".   If necessary, User-Telnet would notify Server-Telnet about the new   effective page size.  User-Telnet would then map the output data to   the allowed usable space on the screen.   User-Telnet may request OUTMRK data or initiate setup of this   convention at anytime by transmitting "DO OUTMRK".  If a WILL, DO   OUTMRK exchange is not followed by the OUTMRK subnegotiation of the   marking data, the User-Telnet may terminate the output marking option   by sending a "DON'T OUTMRK".Silverman                                                       [Page 3]

RFC 933                                                     January 1985Output Marking Telnet Option   Control Flag      The CNTL flag is defined as:         D = Default, the placement of the markings is up to             User-Telnet.  This is the expected mode for most             interactions.         T = Top, this banner is to be used as the top of the screen.             If multiple output markings are desired, then T and B (or R             & L ) are to be used.         B = Bottom, this banner is to be used at the bottom of the             screen.         L = Left, markings on the left.  (The precise meaning of this             is to be defined.)         R = Right, marking on right.  (The precise meaning of this is             to be defined.)   Banner Data      The use of Carriage Return and Line Feed (CRLF) will be      interpreted as a end of line in the marking banner text.  If the      user wants a multiline banner, CRLF will be used between each      line.  No CRLF is needed at the end of the marking data.      To use multiple banners, all of the banners will be included in      one subnegotiation command of the form:         "IAC SB OUTMRK CNTL data GS CNTL data IAC SE"            where GS is the ASCII Group Separator (29) character.      User-Telnet will be responsible for positioning the marking banner      data on the screen.Silverman                                                       [Page 4]