Telnet Suppress Go Ahead Option
also
- std-29
Extracted elements (13)
Although it is probable that both parties will suppress GO AHEAD in both directions if suppression is used at all, the protocol nonetheless requires independent negotiation per direction to preserve generality.
The option exists because the NVT's half-duplex GO AHEAD signal is unnecessary overhead for a full-duplex connection between a full-duplex terminal and a host optimized for full-duplex operation.
In many Telnet implementations it is desirable to couple SUPPRESS-GO-AHEAD with the Echo option; both options typically must be simultaneously in effect to achieve character-at-a-time echoing by the remote host.
A data sender suppressing GO AHEADs should attempt to actually transmit characters as soon as possible with minimal buffering, consistent with any other active agreements.
GA suppression must be negotiated and applied independently in each direction of the Telnet connection; suppression in one direction does not imply suppression in the other.
The default state is WON'T SUPPRESS-GO-AHEAD / DON'T SUPPRESS-GO-AHEAD, meaning go aheads are transmitted unless the option is explicitly negotiated.
When the SUPPRESS-GO-AHEAD option is in effect between a sender and receiver, the sender need not transmit GAs.
With SUPPRESS-GO-AHEAD in effect, an IAC GA command that is received should be treated as a NOP, although IAC GA should not normally be sent in this mode.
The Suppress Go Ahead option is assigned option code 3. It is negotiated using the standard Telnet WILL/WON'T/DO/DON'T option negotiation mechanism.
IAC DO SUPPRESS-GO-AHEAD: sent requesting that the sender of data start suppressing GA when transmitting, or confirming that the data sender is expected to suppress GA.
IAC DON'T SUPPRESS-GO-AHEAD: sent demanding that the receiver start or continue transmitting GAs when transmitting data.
IAC WILL SUPPRESS-GO-AHEAD: sent by a party requesting permission to suppress transmission of the Telnet GA character, or confirming it will begin suppressing GA with transmitted data characters.
IAC WON'T SUPPRESS-GO-AHEAD: sent by a party demanding to begin or continue transmitting the GA character when transmitting data characters.