ArcNet and the Pursuit of Multiple Topologies

From: Pete Turnbull <>
Date: Sat Oct 13 16:37:54 2001

On Oct 13, 13:10, Eric J. Korpela wrote:
> > 100baseTX uses the same pairs as 10baseT.
> >
> I thought that 100bTX uses 3 pairs for full duplex (at least my
> wiring instructions say it uses 1+2 3+6 and 4+5.) Have I gotten some
> misinformation?

Yes, I'm afraid you have! 100baseTX uses the same pairs as 10baseT, no
more, no less. 4+5 are definitely not used. However, they are used
(along with 7+8) for 100baseT4, which uses a different encoding and
modulation scheme to permit 100Mb/s operation over lower-grade cable, using
all 4 pairs, and similarly 1000baseTX uses all four pairs. Nothing I know
of (certainly no standard Ethernet technique) uses three pairs.

In 100baseTX full-duplex (and 10baseT full-duplex which is an extension of
the older standard, not always supported) the same pairs are used for
transmit and receive as in half-duplex. The only difference is that both
pairs are allowed to be active at the same time (which would be counted as
a collision otherwise).

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Sat Oct 13 2001 - 16:37:54 BST

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