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This module describes cable network construction
using coaxial cable. Coaxial cable is basically a copper wire
with some outer layers of insulation and an outer conductor.
This enables the cable to be used to carry data and information.
"Coax" as it is usually referred to, can carry more
information than twisted pair ethernet cable, at a higher
rate, and with less signal loss (attenuation) and distortion.
Coaxial cable is available in various sizes (3/4", 5/8",
1/2"), which allow it to carry different amounts of data
over greater or lesser distances before another device, such
as an in-line signal amplifier needs to be installed. As an
example, 1/2" coax can carry a signal approximately 1350
feet before another device is required.
Coaxial cable installation is described
in detail in this module, to show what a community will need
to do in order to network their members using coaxial cable
technology (commonly referred to as "cable"). This
is the same technology that is used to deliver cable television
and radio signals, however this module discusses this technology
as a means of exchanging computer data.
Cable television began to be used as a
method of distribution as it was more efficient to send signals
directly through copper wire than to send them through the
open air as wireless signals. Additionally, this allowed the
cable companies to be selective about what channels they deliver,
and to deliver a larger number of channels. Now, this system
is used as a fast and efficient means to deliver computer
data.
In the past, cable companies would place
a signal splitter or an amplifier on a line anywhere one was
needed, in order to bring service to additional customers
(shown below). The more devices and the more distance of cable
in a system meant that larger amounts of signal were being
lost.
When this happened, the company would install
a signal amplifier, however this meant that the poor signal
(which had already lost both strength and quality) would be
amplified. This resulted in a poor quality system that was
difficult to troubleshoot, and where there was no control
from a central location over the final signal quality throughout
the system. Additionally, it meant that if a part of the system
went down, generally the entire system would fail.
Use of cable systems for data requires
a much better quality and much more consistent signal. This
is because the data is running essentially "on top"
of a cable TV signal, and requires a larger volume of information
to pass through the system unchanged in order for it to work
properly. In order to provide consistent data service, the
system needs to be clean, with no leakage.
For this reason, a new system for cable
plants was developed. This system is now the most common type
of cable system, and is referred to as a "trunk-bridger"
system. Using this system, signal quality can be controlled
from one location, and maintained throughout the distribution
area with very little loss of signal strength or quality.
Trunk-bridger systems work by running one
main line or "trunk", from the head end, which then
feeds bridges (branches off of the system) which run to different
service areas from the main line. Lines are then taken off
of the bridge systems to feed individual users. This system
makes it easier to locate problems, and enables the entire
system to stay functional when there is a problem with one
or more bridges. Individual branches that are experiencing
problems within this system are much easier to locate and
fix, unlike the old "random" system, where it was
virtually impossible to locate and troubleshoot a problem
in the system.
When planning a trunk-bridger system, the
idea is to create a main line in which there is no degradation
or loss of the original signal through an area. This "clean"
signal is then used as the basis for delivering services through
an area, and can be maintained at a higher quality through
proper installation techniques.
The multiple phases required in creating
the required cable infrastructure to deliver broadband internet
data service will be described in detail in this module, including:
licensing requirements, putting up a cable "plant,"
and bringing in and delivering a signal to the users.
Creativity and resourcefulness when planning
the cable plant are crucial, and can save communities a great
deal of money. Before deciding to purchase an entirely new
system, check to see if there is an abandoned cable plant
in the area. It may be possible to utilize some of the old
cable, and choose equipment to make the existing plant useable
for current and future needs. It may also be possible to modify
an existing "dark" (i.e. not being used or abandoned)
cable plant, to make it into a useful trunk-bridger system.
If there is an opportunity for taking over
an abandoned cable plant, review the local regulations, as
well as any cable or hydro regulations. Licenses are still
required to distribute a signal, however it may be possible
to simply claim an abandoned plant. Further to this, cable
companies often upgrade their systems. Old equipment can still
be very useful, and can sometimes be purchased at much cheaper
prices than purchasing new equipment. This is an excellent
inexpensive way for a community to begin cable plant installation,
but probably requires some creative thinking and resourceful
searching to become reality.
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