AIUI, the lan cabling base rates are UTP (or STP) ethernet 10BaseT, 100BaseT or
1000BaseT. This means that the "data transfer rate" is either 10Mb/s, 100mb/s or
1000Mb/s.

There is no MHz transmission bandwidth involvement at all.

I get boggled between MB's and Mb's so I tend to think in Mhz or Ghz.
To me, a bit is a transition from 0 V to max +ve (maybe 5V or 15V)
then back to 0. IMHO, the only time to worry is when a constant stream
of 1's and 0's is being sent. Then the voltage is being switched on
and off regularly with a 0 between 1's. That to me is a full cycle
which can be expressed as 1 hz, with the negative cycle missing.

I realize it's not technically correct but we're not concerned with
the number of bits as much as we're concerned about the bandwidth,
frequency-wise. In other words, what would be the difference between a
100 Mhz analog square wave transmission and a 100 Mb/s transmission of
alternating 1's and 0's?

With respect to what you said about the data transfer rate, you have
to be a lot more careful. Data is not necessarily 1's and 0's, it
could be ASCII throughput which is measured in bytes per second. Data
has to be meaningful and you have to specify whether it's being sent
on a carrier. In fact, the modulation protocol determines a lot about
the transmission, and that's why the MMC code, etc., was developed.

Schemes like that get higher throughput by manipulating the data. When
several 1's appear in a sequence, or several 0's, they have a way of
transmitting that information at a lower throughput.

When they measure CAT 5 throughput, they are talking bandwidth, which
is the number of 'bits' you can transfer in 1 second. There is no such
thing in CAT5 or 6 technology as a 1 Gb/s throughput on a single
pair. It is simply not possible. I was questioning their claims for an
actual 100 Mb/s throughput since that kind of frequency is generally
not seen in practice. I'm sure it has been done in the lab and that it
can be reproduced, but at 100 Mh/z you have a lot more to worry about
in a big system such as overall radiation from the wiring system.

Like I said, many systems are regulated by governments that limit them
to a throughput of 30 Mhz. Even if CAT 5 can pass 100 Mhz on a single
pair in a lab, where is that ever used in practice? DSL is being
passed on cable with bandwidths that can't exceed 10 Mhz. How is that
done? It's done with modulation tricks that pass more information on a
lower bandwidth line.