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446 BROADBAND NETWORK INFRASTRUCTURE
Local TV
Stations
Figure 9.9
National TV
Networks
Head End
• •
Coax Trunk
Traditional analog CATV network, with tree - and - branch architecture.
analog, coax - based, one - way networks for the downstream delivery of analog entertainment
TV. Few changes occurred in CATV networks until the 1990s.
Beginning in the mid - 1990s, a few large CATV providers began to upgrade their
aging coaxial cable systems. As many of those networks were installed in the late
1960s and early 1970s, they were in awful shape. Further, those networks were
strained for capacity as the CATV providers sought to increase revenues and profi ts
through the introduction of premium movie channels and Pay - Per - View (PPV). The
upgrades, in some cases, went beyond simple coax upgrade and replacement to
include optical fi ber in the trunk facilities from the head end to the neighborhood,
where they terminated in an optoelectric conversion box that interfaced with the
existing coax for ultimate termination at the premises.
As the telecommunications domain in the United States was deregulated with
the Telecommunications Act of 1996, the CATV providers began to consider operating
as CLECs. The technology existed to upgrade the coaxial cable system to support
two - way communications through frequency splitting and advanced signal modulation
techniques, much as is done over twisted pair in xDSL technologies. The coax
amplifi ers and set - top boxes could be upgraded as well. Further, the system could
be converted to digital by replacing the amplifi ers with repeaters, and TDM channels
could run inside the FDM channels, much like xDSL. The coax cable certainly offers
much more in the way of bandwidth and distance than does twisted pair, and with
an upgrade, error performance could be improved to levels that would make twisted
pair pale by comparison. With optical fi ber in the long - haul portion of the network
(i.e., from the head end to the neighborhood), it became clear that CATV systems
could compete very effectively with the ILEC local loop. Further, the largely unregulated
CATV providers could not be forced to wholesale their local loops to com-
Coax
Bridge
Distribution
Tap