ArcNet and the Pursuit of Multiple Topologies

From: Ethan Dicks <>
Date: Mon Oct 15 13:18:10 2001

--- "Eric J. Korpela" <> wrote:
> > On the Ethernet side, I'd not worry about specific 10bT and ThickNet
> > segments.
> Just wired the house with Cat-5 this week. 10bT has the advantage that
> it's also 100bT with a change of equipment.

I know you probably know what you meant, but to me, that statement is
misleading, or rather, to someone who knows little about networking,
taking the second sentence out of context could lead trouble.

phone wire - 2 pair or more, good for analog telephones
CAT-3 - will pass 10mbps traffic (or analog telephone traffic)
CAT-4 - good for token ring
CAT-5 - good for most inexpensive networking technologies
CAT-5e - needed for transmission technologies that put > 100mbps on
             a single pair.

10BaseT can use CAT-3 or better. 16mbps Token Ring needs CAT-5 or
better. 100Base-TX needs CAT-5 (including CAT-5 jacks!) Don't recall
what 100Base-T4 needs (uses more than 2 pairs in the cable to lower the
required per-pair-bandwidth).

I mention jacks because I have a pile of punchdown blocks, etc., that
came from a sheet of plywood at a former employer's access point when
we ripped out the Token Thing hardware and installed CAT-5 (and new
wires). I would not expect to be able to use these blocks in a 100mbps
environment. I did get a nifty Nevada Western 19" rack-mountable RJ-11-
to-RJ-21 (Telco 50) patch panel that the baluns hung off of, if I ever
decided to do IBMish things at home.

Yes, you can untwist things past 1cm and still ring out as CAT-5 from end
to end, but the further you deviate from the published spec, the shorter
haul you can expect true CAT-5 performance out of your network. Same
with using video coax cable (RJ-62) for Ethernet (RG-58) - 75 ohms
impedance vs. 50 ohms. In small enough doses, it appears to work; but
as the network grows, the little analog effect do have an impact.

Lotsa little fiddly details about the physical layer are covered up by
robust layer 2 and layer 3 protocols. Without expensive sniffer hardware
(Time Domain Reflectometer, anyone?), a lot of this stuff gets swept under
the rug until you are having fits when it doesn't work.


> (ISTR that you can use the
> unused pair in the cable for LocalTalk, but I haven't yet tried it).

Should be able to.

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Received on Mon Oct 15 2001 - 13:18:10 BST

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