Thicknet/10base5 Test Segment: The Cable is In!

[Eric Smith]

On Wed, Jun 27, 2018 at 10:59 AM, Paul Koning <paulkoning at comcast.net>
wrote:

> > On Jun 27, 2018, at 12:36 PM, Eric Smith via cctalk <
> cctalk at classiccmp.org> wrote:
> > Collision detection was the reason (or at least _a_ reason) why the
> spacing
> > of taps on the 10BASE-5 "thick" Ethernet cable was required to be an
> exact
> > multiple of 2.5m. It was never clear to me why this was not also a
> > requirement for 10BASE-2 "thin" Ethernet.
>
> Yes, to avoid false alarms.  The purpose of the spacing rule is to ensure
> that there is enough signal integrity that you do not get spurious
> collision indications due to reflections off the impedance variations along
> the cable.  On a segment with few transceivers, there is enough margin that
> the rule doesn't matter.  This is why 10Base-2 doesn't have that rule: the
> station count limit is low enough that it isn't needed.
>

Interesting! I won't disagree with what you're saying, since I'm ignorant
of these details, but in my experience 10BASE-2 networks usually had far
_more_ nodes on a network than any 10BASE-5 network I saw. I routinely saw
over 100 nodes on a 10BASE-2, but I never saw more than 20 or so on a
10BASE-5. (There certainly may have been larger 10BASE-5 networks; I only
ever saw about a dozen 10BASE-5 networks.)