Supress Go-Ahead (SGA)
Option code: 3
See also: RFC 858
Old telnet implementations assumed operating a half-duplex connection. As a consequence once a party finished transmitting, it sent a telnet GA (Go Ahead) command, to inform the other party that it now can send data.
Nowadays half-duplex isn't used anymore and therefore the usage of Go Ahead messages not necessary. With this telnet option, both parties could agree on not using GA messages.
In the context of MUDs the Go Ahead (GA, byte value 249) is sometimes used to indicate the end of a prompt.
| Tokens | Bytes | Meaning |
|---|---|---|
| IAC WILL SUPPRESS-GO-AHEAD | 255 251 3 | The party expresses its wish to not send GA messages. |
| IAC WON'T SUPPRESS-GO-AHEAD | 255 252 3 | The party expresses its wish to start sending GA messages. |
| IAC DO SUPPRESS-GO-AHEAD | 255 253 3 | The party expresses its wish that the other party stops sending GAs. |
| IAC DON'T SUPPRESS-GO-AHEAD | 255 254 3 | The party expresses its wish that the other party starts sending GAs. |
Interworking with ECHO
When the (remote) ECHO is enabled and the SGA telnet option is enabled too, some MUD clients interprete this setup as the request not even to do local line buffering and send every keystroke via telnet. This character-a-time-mode. is some kind of best practice, but not supported by all clients