From: utzoo!henry
Newsgroups: net.unix-wizards
Title: Re: Re:  Padding on Ann Arbor Ambassadors &c 
Article-I.D.: utzoo.2850
Posted: Wed Mar  2 22:45:08 1983
Received: Wed Mar  2 22:45:08 1983

The flow-control-with-XON/XOFF issue has been beaten to death on
at least one other mailing list in the past.  The basic points
that emerged were three:

	1. The DC1 and DC3 characters used in XON/XOFF flow control
	are ASCII ***control*** characters.  Said control characters
	were never intended for use by the user at all, much less to be
	under his "complete control".  The folks who used DC1 and DC3
	(also known as XON and XOFF) for flow control were entirely
	within their rights.  Any software which assumes that control
	characters allocated to device or transmission-link control
	can be send and received as data characters is wrong.  It is
	only an accident that many transmission links pass them intact.
	Note that there is no requirement that ^Q and ^S send DC1 and DC3
	respectively;  they could easily send escape sequences which
	*are* legitimate data and *would* be passed through intact.
	Complain to your terminal manufacturer.

	2. RTS and CTS are not really intended for this job either.
	Nor are they workable for this purpose across networks.

	3. In fact, *none* of the common flow-control protocols are
	practical for network use, because they all rely on "stop, I
	can't take any more" signals which don't work properly when
	transmission delays become substantial.

					Henry Spencer
					U of Toronto