Path: utzoo!attcan!uunet!husc6!think!ames!pasteur!ucbvax!VENUS.YCC.YALE.EDU!LEICHTER
From: LEICHTER@VENUS.YCC.YALE.EDU ("Jerry Leichter ", LEICHTER-JERRY@CS.YALE.EDU)
Newsgroups: comp.os.vms
Subject: re: set host /dte
Message-ID: <8805240455.AA02395@ucbvax.Berkeley.EDU>
Date: 21 May 88 01:11:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 60


	I am trying to hook an X.25 PAD up to an outgoing port on a VAX
	11/785.  I've got the two basically talking using set host/dte, but
	flow control doesn't seem to be working.  What modes do I need to have
	set for the term port in order that CTS/RTS handshaking will work
	correctly?

There is no such setting; the VMS terminal driver does not support CTS/RTS
handshaking.

		    So far I've determined that I need the modem bit set so
	that the connection is correctly terminated when either end
	disconnects (using DTR/DSR).  I would really love to get CTS/RTS going
	instead of XON/XOFF, so that the connections can be as invisible as
	possible.

The only DEC equipment I know of that supports CTS/RTS handshaking is some
recent terminal servers.  You'd have to check the specs to determine which
ones.
		   Also, instead of flow control, is there anything I can do
	to ensure that characters don't get lost, such as a higher process
	priority, larger buffers (in sysgen, and what parameter?), etc?  Oh
	ya, all at 9600 baud.

Nothing except flow control will ENSURE that this will work - any buffers,
any increase in priority, will be overrun by SOME bursts of characters.  The
best you can do is minimize it.  Unless your system is very heavily loaded,
increased priority probably won't make much difference; but a larger terminal
buffer may help.  The SYSGEN parameter TTY_TYPAHDSZ controls the size of the
typeahead buffer.  I would not, however, recommend increasing this:  EVERY
terminal will use that many bytes of physical - not virtual - memory for
typeahead.  On a large system, this can add up.  Rather, set the SYSGEN
parameter TTY_ALTYPAHD, the "alternate" typeahead buffer size; then set the
terminal you will be using with SET HOST/DTE to /ALTYPEAHD/PERMANENT.  This
will cause that terminal line to use ALTYPAHD, rather than TYPAHDSZ, for the
size of it's typeahead buffer.  Note that once set, /ALTYPAHD cannot be
cleared short or rebooting the system.

	(In desperation, I figured I'd try XON/XOFF to see if at least that
	worked, and of course, it didn't seem to.  I must be off in left field
	on this...)

How did you "try XON/XOFF"?  Note that there are TWO setting of significance
here:  /TTSYNC is the parameter you usually think of; setting it says that
an XOFF received by VMS causes it to suspend output, and an XON causes it to
resume output.  The converse is /HOSTSYNC, which says that VMS is to set XOFF
when the typeahead buffer is (almost) full, XON when it empties out.  Almost
certainly, you are seeing problems when characters arrive from the PAD too
quickly; so it is /HOSTSYNC you need.  Further. THE PAD MUST RESPOND TO THE
XOFF!  This isn't a VMS issue - it's a question of whether your PAD responds
to XON/XOFF from the async line it is connected to.  It may not support this
at all; or you may have to turn it on.  It may also respond, but too slowly -
at 9600 baud, a character arrives about every millisecond.  If the PAD takes
100 ms to respond to XOFF, it may overrun VMS's buffer.  (Things get even
worse if there is a long "pipe" down which the characters must travel.)  If
it is slow response from the PAD that is the problem, an appropriate setting
of TTY_ALTAHD, plus TTY_ALTALARM (which controls the point at which the
terminal driver will generate an XOFF), should allow you to fix the problem.

							-- Jerry