In article <6kbq14dcktl70q0h6i9dtt0h6c9u7f5kch@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

> I once calculated the maximum cable length at about 1,200ft for
> 10baseT-HDX before timing becomes an issue. Why 2,000ft worked is
> still a mystery to me. It shouldn't have unless the timing on the
> ethernet devices is more relaxed than required.

The propagation velocity of UTP is about 5.1 ns/meter, or roughly
1.5 ns/foot. Your 2,000 foot run has a round-trip delay of around 6 us,
which is far less than the 48 us allowance in half-duplex 10 Mb/s
Ethernet (i.e., 51.2 us less the 3.2 us "jam" time). As long as the
*signal characteristics* were still acceptable to the line receiver, it
should work, as there are no protocol timing violations in this
arrangement.

Much of the timing allowance in ordinary networks is allocated to the
repeaters; I suspect that your setup was a two-station back-to-back
connection, which has LOTS of timing margin.

> Also, note that I was
> using 10baseT-HDX (half-duplex). Full duplex and/or 100baseT will not
> work due to collision domain issues and cable near end crosstalk.

Backwards. The collision domain (timing) issues are related only to
*half* duplex Ethernet, not full duplex. You can (and we often do) run
full-duplex Ethernet over tens or hundreds of kilometers (using fiber)
with no timing concerns.

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