From:	MERC::"uunet!CRVAX.SRI.COM!RELAY-INFO-VAX"  8-FEB-1993 01:21:26.65
To:	info-vax@kl.sri.com
CC:	
Subj:	Re: How does a program know when it's being stopped?

In article <1993Feb5.154202.4436@iscnvx.lmsc.lockheed.com>,
 burkhardt@SKYNET.SSD.LMSC.LOCKHEED.COM (Spike Burkhardt) writes:
> In article <C1xrL1.8M0@nmrdc1.nmrdc.nnmc.navy.mil>,
> dsc3pzp@nmrdc1.nmrdc.nnmc.navy.mil (Philip Perucci) writes:
>>Is it possible to run Async DECNET through a terminal server, rather than
>>RS-232 lines directly connected to BI/XMI bus?

Terminology nitpick:  What you're asking about is "asynchronous DDCMP", not
"asynchronous DECnet". 

That aside... it is not possible to run async DDCMP through a LAT terminal
server port and guarantee that it will work in all cases.  The reason, as I
understand it, is that the async DDCMP terminal class driver (NODRIVER) has
time constraints that *will* sometimes be violated when the characters being
sent and received are moving via LAT over Ethernet to a terminal server.

For this reason, async DDCMP over LAT has always been unsupported.  Which is
not to say that it will never work:  A few people try it and get great results;
some people try it and end up with a low level of errors (which the DDCMP
protocol corrects, at some cost in throughput); and of course some have tried
it and failed miserably (when the traffic to correct the errors introduced by
the timing problems exceeds the original traffic). 

DEC has gotten so tired of dealing with support calls from the latter group
that in Version 5.5 they put in a change so that SET TERMINAL /PROTOCOL=DDCMP
won't work at all on LAT devices.  I understand, though, that you can get a
patch from CSC to enable it (presumably after swearing up and down that you
won't call for support if it doesn't work for you). 

All in all this wouldn't be my choice of a communication link for any sort of
mission-critical application.  Perhaps the worst scenario of all: you may try
it and find that it works now, but later on when your network, the LAT box, 
and the host VAX all have more work to do, your async DDCMP link (upon which
you may have come to depend) starts having problems. 

But, if you want to try it anyway -- if you are running on VMS 5.4 or earlier,
go ahead and try it; it might work, but don't complain to DEC if it doesn't. 
If you're running 5.5[-n], and you have CSC support, ask for the "async DDCMP
over LAT" patch -- but again, if it doesn't work, don't complain to DEC; it
isn't guaranteed to.  

What is the application for the DECnet connection?  If it's just file transfers
to or from another VMS system, or even a Unix, MS-DOS, Mac, or any of several
other types of systems, you might look at using Kermit or DECUS uucp. :-) 
Those WILL run over LAT ports, and they're free. 

	--- Jamie Hanrahan, Kernel Mode Systems, San Diego CA
drivers, internals, networks, applications, and training for VMS and Windows NT
uucp 'g' protocol guru and release coordinator, VMSnet (DECUS uucp) W.G., and 
Chair, Programming and Internals Working Group, U.S. DECUS VMS Systems SIG 
Internet:  jeh@cmkrnl.com, or hanrahan@eisner.decus.org  Uucp: uunet!cmkrnl!jeh