Telnet terminal speed option

The option is explicitly modelled on RFC 930 (Telnet Terminal Type Option), reusing its negotiation structure and much of its text to maintain consistency across Telnet option specifications.

The option is motivated by the fact that most operating systems track terminal bit rates for timing-dependent processes such as padding and speed-tuned user interfaces; the option extends this capability to Telnet connections where the speed is not directly known.

Many systems allow only certain discrete terminal speeds. When a received speed does not match an allowed value, implementations should pick the nearest allowed speed, rounding in the safe direction (e.g., rounding up when speed is used for padding, since too much padding is better than too little).

IAC DO TERMINAL-SPEED indicates the sender is willing to receive terminal speed information in a subsequent sub-negotiation.

IAC DON'T TERMINAL-SPEED indicates the sender refuses to accept terminal speed information.

IAC WILL TERMINAL-SPEED indicates the sender is willing to send terminal speed information in a subsequent sub-negotiation.

IAC WON'T TERMINAL-SPEED indicates the sender refuses to send terminal speed information.

Only the sender of DO TERMINAL-SPEED may send SEND requests (IAC SB TERMINAL-SPEED SEND IAC SE), and only the sender of WILL TERMINAL-SPEED may transmit actual speed information (IAC SB TERMINAL-SPEED IS ... IAC SE).

Terminal speed information may not be sent spontaneously; it may only be transmitted in response to an explicit SEND request.

The default state is WON'T TERMINAL-SPEED and DON'T TERMINAL-SPEED, meaning terminal speed information will not be exchanged unless both sides negotiate otherwise.

WILL and DO are used only to obtain and grant permission for future sub-negotiation discussion; actual speed exchange occurs within option subcommands.

The IS subcommand (code 0) is sent as IAC SB TERMINAL-SPEED IS ... IAC SE to convey the sender's terminal speed in NVT ASCII.

The SEND subcommand (code 1) is sent as IAC SB TERMINAL-SPEED SEND IAC SE to request the receiver to transmit its terminal speed.

The TERMINAL-SPEED Telnet option is assigned option code 32. It allows two Telnet hosts to negotiate and exchange the terminal speed (bit rate) of the connection.

Terminal speed is encoded as an NVT ASCII string containing the decimal transmit speed, a comma, and the decimal receive speed, e.g., "9600,100". No leading zeros and no extraneous characters such as spaces are permitted.