RFC 1372 (rfc1372) - Page 2 of 6
Telnet Remote Flow Control Option
Alternative Format: Original Text Document
RFC 1372 Telnet Remote Flow Control Option October 1992
IAC DONT TOGGLE-FLOW-CONTROL
Sender refuses to send command to enable and disable flow control.
IAC SB TOGGLE-FLOW-CONTROL OFF IAC SE
Sender requests receiver to disable flow control.
IAC SB TOGGLE-FLOW-CONTROL ON IAC SE
Sender requests receiver to enable flow control.
IAC SB TOGGLE-FLOW-CONTROL RESTART-ANY IAC SE
Sender requests that when flow control is enabled, the receiver
allow any character (except another XOFF) to restart output.
IAC SB TOGGLE-FLOW-CONTROL RESTART-XON IAC SE
Sender requests that when flow control is enabled, the receiver
allows only the XON character to restart output.
3. Default Specification
The default specification for this option is
WONT TOGGLE-FLOW-CONTROL DONT TOGGLE-FLOW-CONTROL
meaning flow control information will not be exchanged in either
direction.
4. Motivation
This memo describes a method of remotely toggling flow control
between a user telnet process and the attached terminal. Only flow
control of data being transmitted from the telnet process to the
terminal is considered. Many systems will also allow flow control of
data from the terminal to the telnet process, however there is seldom
need to change this behavior repeatedly during the session.
There are two common ways of doing flow control: hardware and
software. Hardware flow control uses signals on wires dedicated for
this purpose. Software flow control uses one or two specific
characters sent along the same path as normal input data. Most
commonly, XOFF (control-S) and XON (control-Q) are used to stop and
start output, respectively. The option described herein is useful
primarily where software flow control is being used. (Since hardware
flow control does not preempt any characters, there is normally no
Hedrick & Borman