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
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