In the coax portion of the plant, the cable
is split at each branch using a passive device known as a tap. This plant topology was
originally designed to handle one way communications from a Community Antenna
Television (CATV) operator??™s head-end to subscriber residences, and for that purpose,
it is an efficient and high-performance topology. Return signals, however, are not handled
as efficiently, nor with as high a performance level. In particular, the branching
structure of the cable network offers many points for noise and interference to enter
the plant and be carried to the head-end. Each unterminated connector in a subscriber
location is an opportunity for the ingress of noise and interference that affects all customers
served by the same fiber node. This property has been termed noise funneling
and results in a significantly lower signal-to-noise ratio in the return path relative to
the forward path.
Spectrum Allocations A modern cable system is capable of fully bidirectional communication.
The optical fibers between the head-end and the fiber nodes carry downstream
(from the head-end to the customer) and upstream (from the customer to the head-end)
signals on separate fibers, whereas the two signals are intermixed on the coax portion
of the plant.
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