Output marking Telnet option

　　Network Working Group S. Silverman

　　Request for Comments: 933 MITRE-Washington

　　January 1985

　　OUTPUT MARKING TELNETOPTION

　　Status of this Memo

　　This RFCproposes 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 27

　　2. 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).

　　RFC933January 1985

　　Output 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 initial　RFC933January 1985

　　Output 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".

　　RFC933January 1985

　　Output 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.