RFC1097 - Telnet subliminal-message option

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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 RFCspecifies 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

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

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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