From:	SMTP%"raspuzzi@mrlat.enet.dec.com" 13-MAY-1994 09:11:55.75
To:	EVERHART
CC:	
Subj:	Re: Async DecNET via LAT port

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From: raspuzzi@mrlat.enet.dec.com (Michael Raspuzzi)
Subject: Re: Async DecNET via LAT port
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Reply-To: raspuzzi@mrlat.enet.dec.com (Michael Raspuzzi)
Organization: Digital Equipment Corporation
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Date: Wed, 11 May 1994 13:21:14 GMT
To: Info-VAX@CRVAX.SRI.COM
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In article <14283.9405101129@cs3.brookes.ac.uk>, s5802362@cs3.oxford-brookes.ac.uk (featherstone pg) writes:
|>Hi All,
|>
|>Is it possible to have asynchronous DECNet via a LAT port.  I know the Pathworks
|>manual says that it is not possible, but I have read somewhere that it is (BUT
|>it does say DEC doesn't support it !!).
|>
|>If it is possible, how ?
|>

In OpenVMS VAX V5.4 or lower, it was possible to jury-rig async DECnet over
LAT.  In OpenVMS VAX V5.5 or higher, it will not work.  Attempting to set
up a LAT device for async DECnet will result in an SS$_UNSUPPORTED error
code.

In OpenVMS VAX V5.5 LAT software, a whole bunch of programming functions
were added so that a systems programmer can change LAT parameters via
a program with $QIO LAT SETMODEs and read them back with $QIO LAT
SENSEMODE operations.  These new $QIO functions were designed as buffered
I/O functions.  When setting a terminal UCB up for async DECnet, certain
operations require the ability to do direct I/O.  If a direct I/O request
is handed to LTDRIVER through an LTA device, bad things happen in I/O
post processing (like system crashes).

For the most part, async DECnet would work but this would leave a system
open to a crash at some point (and the worst part about it, the crash could
be caused by a clever non-privileged user).  For now, we choose to disallow
the conditions that can cause the system crash.  There have been thoughts
tossed around for possibly allowing async DECnet over LAT in a future
OpenVMS release.  If we decided to open up support for it, the system
crash will be taken care of and we will document what can and can't be
done (not all of the various methods for setting up async DECnet will
work with LAT).

-- 
Mike Raspuzzi (raspuzzi@mrlat.enet.dec.com)
Digital Equipment Corporation