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

From: Pete Turnbull <pete_at_dunnington.u-net.com>
Date: Sat Mar 24 16:32:01 2001

On Mar 24, 9:44, Bill Gunshannon wrote:
> On Sat, 24 Mar 2001, Pete Turnbull wrote:

> > 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
> > 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.

As far as I've seen, it's always been available in 100m and 500m drums --
which of course happen to be multiples of 2.5m -- but I'm sure that's just
because they're nice round numbers. Most cable is sold in those
One of my catalogues does list 10,20,30, and 40m lengths fitted with
N-connectors, but again I'm sure that's just because they're round numbers.

> 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.

> > I've never been aware of a problem with that. Our old Departmental
> > (installed by my predecessors) consisted of several segments, many of
> > had lots of N-series transceivers in them. I suppose, though, that
> > using N-series transceivers, it might make some sense to chop out a
> > 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.

Agreed, but that was *common* 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!!)

Yup, I know! I saw what hapenned when someone tried that :-) It did *not*
do anything any good at all! I also know what can happen when the unwary
(in this case, me) touch the screen while holding on to a locally-earthed
cabinet :-)

> Or thin-net installations with a length of RG58 between the T-connector
> and the transciever.

I know someone who tried that, too. It worked for a couple of short tees,
but after that everything fell apart. I know of a few installations which
use Safernet and EAD cable to prevent people trying it.

> > 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.

I have a pair of FOIRL transceivers and some fibre for exactly that, but
people still are interested to see real Ethernet.

> 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.

I'd like to get a vampire tap for my collection -- all of ours were
N-series, at least all the ones I've found.

Pete						Peter Turnbull
						Network Manager
						Dept. of Computer Science
						University of York
Received on Sat Mar 24 2001 - 16:32:01 GMT

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