RFC 1080 (rfc1080) - Page 1 of 4

Telnet remote flow control option

Network Working Group                                         C. Hedrick
Request for Comments: 1080                            Rutgers University
                                                           November 1988


                   Telnet Remote Flow Control Option

Status of This Memo

   This RFC specifies a standard for the Internet community.  Hosts on
   the Internet that do remote flow control within the Telnet protocol
   are expected to adopt and implement this standard.  Distribution of
   this memo is unlimited.

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
   need to disable it.)

   The primary difficulty with software flow control is that it preempts
   one or two characters.  Host software often requires the user to be
   able to input every possible ASCII character.  (Certain editors are
   notorious for having XOFF and XON as commonly-used commands.)  For
   this reason, operating systems often allow programs to disable flow
   control.  While it is disabled, the characters that normally signal
   flow control may be read as normal input.  In a telnet environment,
   flow control is normally done by the user telnet process, not by the
   host computer.  Thus this RFC defines a way to propagate flow control
   status from the host computer to the user telnet process.








Hedrick