RFC 1372 (rfc1372) - Page 2 of 6

Telnet Remote Flow Control Option

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