10Base5/Thicknet (was Re: SUN networking problems)

From: Bill Gunshannon <bill_at_cs.scranton.edu>
Date: Sat Mar 24 08:44:41 2001

On Sat, 24 Mar 2001, Pete Turnbull wrote:

> On Mar 23, 17:42, Bill Gunshannon wrote:
> >
> > Two points.
> >
> > First, "a piece" of yellow cable won't work. The lengths were part of
> the
> > spec and very important. Having to do with reflections and such (anybody
> > here still have a TDR??)
> I've not seen anything about lengths, except of course for the maximum
> length and multiple-of-2.5m tap separation. I'm told the standard
> specifically allows for lengths to be joined at intervals which are *not*
> multiples of 2.5m, and the overall length does not have to be an exact
> multiple either.

Well, I could be wrong, but back in the days when I actually did this
stuff for real I know I never saw yellow cable sold in bulk. Only in
fixed lengths. One would hardly expect they did this if there was no
reason for it. I doubt I still have any catalogs from those days to
look at. In any case, I doubt anyone is going to do a real network today
with an really long sections of yellow cable.

> > Second, The cable is marked with black stripes. The taps must go on
> these
> > stripes. While I have known people who put the transcievers with the N
> > type connectors between yellow segments and on the ends of yellow
> segments,
> > I have never known seen it recommended that you could/should cut the
> cable
> > to insert one of these. I fear that after one or two of them, you would
> > move the spacing between tap locations enough to adversely effect your
> > network.
> I've never been aware of a problem with that. Our old Departmental network
> (installed by my predecessors) consisted of several segments, many of which
> had lots of N-series transceivers in them. I suppose, though, that when
> using N-series transceivers, it might make some sense to chop out a small
> piece of coax rather than just cutting it.

Boy, that sounds scary. But then, what you see in practice does not
always reflect good practice. In the early days of ethernet, all kinds
of strange (and even dangerous) things were done. Like grounding both
ends of the yellow cable (no, you are not supposed to do that!!)
Or thin-net installations with a length of RG58 between the T-connector
and the transciever.

> Unless someone can correct my assumptions, of course!

It has really been a long time since I did my last yellow cable installation.
It was long enough to be close to the maximum and neither fun to install or
maintain. It had dozens of vampire tap transcievers and was aloso connected
a repeater that supported thin-net segments. Before it went away, it had
numerous twisted-pair (not 10BaseT, this was before the standard caem into
being, Synoptics Lattisnet) segments as well. Somehow, I don't miss that
work much.

> > This is, of course, assuming a production network and not two machines.
> > But then. if all you had were two or three machines, a couple hundred
> > feet of yellow cable seems pretty silly.
> Unless they're a long way apart, or you're doing it for
> demonstration/nostalgic/"because it's there" purposes :-)
I can see doing for demonstration purposes, but I would bet people would
be more impressed if it was fiber. That's what I use small demos.

By the way, while I am serious about taking any PDP donations, this
ethernet stuff I have is really free to anyone who want's to pick it
up. And I may be able to find stuff (like vampire taps) at work as
although it is all inactive, I doubt that the yellow cable has been
removed from the ceiling and wiring closets. Who knows, maybe they
would even be glad to have the yellow cable pulled out too. It's a
pretty long run (the length and height of the building) in two sections.

Anybody interested??


Bill Gunshannon          |  de-moc-ra-cy (di mok' ra see) n.  Three wolves
bill_at_cs.scranton.edu     |  and a sheep voting on what's for dinner.
University of Scranton   |
Scranton, Pennsylvania   |         #include <std.disclaimer.h>   
Received on Sat Mar 24 2001 - 08:44:41 GMT

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