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Q19: What is Thicknet?
A19:Thicknet is the 50-ohm "thick" (10mm) coaxial cable used
with Ethernet 10Base5 networks.10Base5 is the original Ethernet system
that supports a 10 Mb/s transmission rate over a 500 meter maximum supported
segment length.
Thick Ethernet coaxial cabling includes a "mark" every 2.5 meters
to indicate proper placement of the 10Base5 transceivers (or MAUs) used
to connect stations to the network. Transceivers may be placed at any
multiple of 2.5 meter intervals. This minimizes signal reflections that
may degrade the transmission quality of the cable segment. The outer jacket
of Thick Ethernet cables is typically a bright color (often yellow) with
black bands at 2.5 meter intervals to mark valid transceiver placement
points.
10Base5 transceivers are attached through a clamp that makes physical
and electrical contact with the cable. They are also called "transceiver
taps" because they are connected through a process known as "tapping"
that drills a hole in the cable to allow electrical contact to be made.
The transceivers are called "non-intrusive" taps because the
connection can be made on an active network without disrupting traffic
flow.
The standard allows a 10Base5 coaxial cable segment to be up to 500 meters
in length. Up to 100 transceivers may be connected to a single segment
at any multiple of 2.5 meters apart. A 10Base5 segment may consist of
a single continuous section of cable, or be assembled from multiple cable
sections that are attached end to end. If multiple cable sections are
used, it can result in "impedance mismatches" that are caused
by slight differences in the impedance of each cable section. When excessive,
these mismatches can cause signal reflections that result in bit errors
and discarded frames. Segments with multiple sections are often built
with cable that comes from a single spool. This ensures each section of
the cable segment will have consistent impedance since it was built by.
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