Typically,
CATV networks are built as hybrid fiber-coax (HFC) structures with fiber spanning
between a video head-end or a hub to a curb optical node, with the final drop section
deployed using standard coaxial cable technology and repeaters (amplifiers) and tap
couplers to split the signal among many subscribers. Faced with the growing competition
from telecom operators in providing Internet services, cable television companies
responded by integrating data services over their HFC cable networks, which, in turn,
required replacing single direction (downstream) signal amplifiers with bidirectional amplifiers,
in order to enable the upstream data path. An updated medium access protocol
was also required to allow access of multiple subscribers to the same shared transmission
channel, while avoiding collisions between individual data transmissions. However,
since most of the usable transmission spectrum is tieddown with TV signal delivery, both
downstream and upstream channels in such systems are very limited in bandwidth, thus
providing decent access rates for only a limited number of subscribers.
It is interesting to note that, while the highly asymmetric nature of the traffic is
observed in DSL and CATV systems, new and emerging applications tend to drive the
bandwidth ratio toward unity.
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