ArcNet and the Pursuit of Multiple Topologies

From: Chris <>
Date: Tue Oct 16 21:39:41 2001

>When I installed PhoneNet stuff into my mother's all-Mac shop, it
>specifically uses the yellow-black pair of standard (US) phone
>wiring and the documentation explicitly shows it as such. They
>even had a sort-of passive hub for your wiring closet to collate
>all the black-yellow pairs for a larger (floor-sized as opposed to
>room-sized) network. We had six Macs and one LaserWriter on the same
>floor of a smallish retail establishment, so it wasn't a problem.
>I can see networks near the edge of their physical spec falling off
>a cliff, though.

Yeah, phone net was designed with the idea that you would piggy back it
over your existing phone wiring... the theory being that a standard
house/business would be wired either all serial (one jack to the next) or
in a star (all jacks coming back to a central punch block). Following
this assumption, it was specifically designed to work over the unused
pair (being yellow/black in standard station wiring).

All PhoneNet REALLY cares about is having two wires from one box to
either the next box, or to a central hub. It need not be twisted pair,
and it need not be the yellow/black pair. Although, if you choose to use
a different pair, either you need to make sure you wire it to the correct
pins on the jack (and thus fake a y/b) or you will have to cut a custom
wired flat cord as the boxes all expect the wires to be the outer two
wires in an RJ-11. But there is nothing stopping you from using unused
pairs in Ethernet and just use a custom flat cord (or break them out into
their own jack).

The single biggest problem with Phone net that I ran into was it was VERY
picky over the wiring being correct. Unlike phones, you could not safely
reverse pairs in a serial setup. Also, the fact that it expects there to
be either serial wiring, or star wiring falls thru in most phone lines.
And even depending on the unused pairs wasn't a surefire idea. In every
Phone net system I installed, I was forced to do some degree of rewiring,
or correcting the wiring. POTS phones are very forgiving to poor wiring,
and many telco installers use that as an excuse to be lazy. In almost all
POTS phone setups you will find some degree of "non spec", things like
unused pairs not being connected, reversing pairs, mixing star and serial
wiring, tapping mid line into a drop to extend for a new jack. Tapping
was DEATH to phone net, it was the single worst thing you could do, as it
caused things like ghosting (items showing up after they have been
removed, or showing up more than once on the network), and random
dropouts of networked devices. It also proved hard to track, as you
almost had to physically trace every wire, looking for a tap.

But all things considered, phone net was a much more econimical way of
wiring a localtalk network. True localtalk cables were very expensive
compared to cheap 2 pair phone cable, so even with rewiring, it still
worked out to be the less expensive way to go.

Even today, phone net works as a nice quick and dirty network when all
you want is printer sharing. I keep a 25ft retractable cord and phonenet
connectors connected to a Localtalk to Ethernet bridge. It lets me
connect old Macs to the network (or my Newton) on the fly, and I can set
it up anywhere in my office. When I am done, I just unhook the phonenet
box, and let go, the retractable cord rewinds and pulls the box back to
my hub shelf, where it hangs waiting for my next use.


Received on Tue Oct 16 2001 - 21:39:41 BST

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