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From: tedcrane@batcomputer.UUCP
Newsgroups: comp.os.vms
Subject: Re: DEMPR and H4000-AB
Message-ID: <684@batcomputer.tn.cornell.edu>
Date: Tue, 14-Apr-87 14:48:29 EST
Article-I.D.: batcompu.684
Posted: Tue Apr 14 14:48:29 1987
Date-Received: Fri, 17-Apr-87 00:30:31 EST
References: <8704140550.AA29379@ucbvax.Berkeley.EDU>
Reply-To: tedcrane@tcgould.tn.cornell.edu.UUCP (Ted Crane)
Distribution: world
Organization: Program of Computer Graphics, Cornell University
Lines: 37

In article <8704140550.AA29379@ucbvax.Berkeley.EDU> BMW6957@TAMCHEM.BITNET (Brad Wilson) writes:
>I'm a planning to install a thin-wire ethernet to extend our existing
>baseband ethernet.  
>....
>I will not be using any DELNI and I'm a little confused.  Does the
>DEMPR also require the special H4000-BA, ...
>If not, why does a DELNI require the special transceiver only if it's
>connected to a DEMPR?  What have I misread?  Anything?  Any help will
>be greatly appreciated.
>

Well, you're about to do what we did several weeks ago.

We used to have a backbone around our lab with several DELNI's hung off
of H4000's.  Old H4000's, at that.  We took one wing of the backbone and
changed it to a single DEMPR with several thinwire segments.  The DEMPR
is hooked to one of the old H4000's.  This works fine.  We were worried
about the same thing, and just crossed our fingers.

There is also another DEMPR hung off our thickwire backbone.  This one is
also off of an old H4000 and works well.  This particular DEMPR came from
DEC but has been jury rigged for some special effects.  I just mention it
to point out that multiple DEMPR's and DELNI's work just fine.

One interesting note:
During the transition, we hooked the DEMPR up to a DELNI instead of directly
to the H4000.  It "sort-of-didn't" work.  Some of the combinations of
thick-to-thin and thin-to-thin couldn't talk to each other, and other
combinations worked ok.  We could not pin the problem down to any specific
"thick"ness of wire, protocol (we have DECnet, TCP/IP, and LAT on the wire),
or hardware (we have DEC, HP, and PROnet stuff on the wire).
However, since we had several DELNI's, we though to swap the one which the
DEMPR was hooked up to with another.  Lo, and behold.  Everything worked OK!
The two DELNI's were listed as the same model, rev, etc.

Would anyone care to comment on this wierdness, or shell we chalk it up to
causes beyond the other side of nowhere?