Xon/Xoff State Control for Telnet Com Port Control Option
draft-edwards-telnet-xon-xoff-state-control-00

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Internet Draft                                             Grant Edwards
<draft-edwards-telnet-xon-xoff-state-control-00.txt>        Comtrol Corp
Intended status: Experimental                             March 23, 2010
Expires September 23, 2010

       Xon/Xoff State Control for Telnet Com Port Control Option
          <draft-edwards-telnet-xon-xoff-state-control-00.txt>

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Edwards                Expires September 23, 2010               [Page 1]
Internet Draft     Telnet Xon/Xoff Flow State Control     March 23, 2010

Abstract

   This document defines new values for use with the telnet com port
   control option's SET-CONTROL sub-command defined in RFC2217.  These
   new values provide a mechanism for the telnet client to control and
   query the outbound Xon/Xoff flow control state of the telnet server's
   physical serial port.  This capability is exposed in the serial port
   API on some operating systems and is needed by telnet clients that
   implement a port-redirector service which provides applications local
   to the redirector/telnet-client with transparent access to the remote
   serial port on the telnet server.

1.  Introduction

   When a telnet server acting as a serial device server (as shown in
   the figure below and also described in [RFC2217]) is configured to
   use Xon/Xoff outbound flow control, it maintains an internal state
   variable that reflects whether or not it is currently allowed to
   transmit data via the physical serial port.  When the telnet server
   receives an XOFF character via the physical serial port, the server
   will stop transmitting data via the physical serial port until an XON
   character is received via the physical serial port.

        +-----------+   telnet/RFC2217
        |  telnet   |   connection          physical
        |  client   +----+                / serial port
        |           |    |               /
        +-----------+    |              /
                         |             /
                    +----+----------+ /
                    |               |/    RS-232      +----------+
                    |   telnet     ++      with       |  serial  |
                    |   server     |+-----------------+  device  |
                    |              ++    Xon/Xoff     |          |
                    |               |      flow       +----------+
                    +---------------+     control

   This memo extends that behavior by defining new telnet com port
   control option [RFC2217] SET-CONTROL subcommand values that allow the
   telnet client to force the server to behave as if an XOFF or XON
   character has been received via the physical serial port.

   This extension is needed by telnet clients that implement a port-
   redirection service in order to provide other local applications
   access to the remote serial port (physically located on the telnet
   server) via the same serial port API that is used to access local
   serial ports.  Since some operating systems provide in the serial
   port API a mechanism to control the state of the outbound Xon/Xoff
   flow control, the telnet com port control option is extended to

Edwards                Expires September 23, 2010               [Page 2]
Internet Draft     Telnet Xon/Xoff Flow State Control     March 23, 2010

   provide a corresponding mechanism.

   This ability to control the internal state of the Xon/Xoff flow
   control feature is not provided by [RFC1372] "Telnet Remote Flow
   Control Option" which provides a way to enable and disable the