unexpected tty behavior

[utzoo!decvax!ucbvax!unix-wizards]

>From saks at LL-XN Wed Sep  2 13:11:07 1981
	Has anybody seen the following phenomenon and, if so, are there
any known solutions?

	On our PDP-11's running UNIX V7 we have several computers hanging off
DZ-11 9600 baud TTY lines.  Communication with these computers is by programs
which specify TANDEM (and CBREAK) for the lines in order to have XON/XOFF
flow control in effect when the downline computer is sending characters to
the UNIX computer.

	We encounter a sporadic output of spurious characters other than 
DC3 (to stop the downline computer from squirting characters at UNIX)
and DC1 (to tell the downline computer to resume sending).
Most of the time these characters are ^T (octal 24) but others have
been observed.  Sometimes the DC1 seems to get lost (clobbered?) causing
transmission from the downline computer to come to a screeching halt.
While this is going on the user program running in UNIX is absorbing the
input characters and is not outputting anything;  this makes it easy to
put a scope on the line and watch output from UNIX.  When we do this we
see a string of DC3's, followed some time later by a DC1.  But, occasionally
we see the strange characters.

	Thank you.
		Francis (fb at ll-xn)