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cable TVThe transmission of TV programs into the home and office via coaxial cable. The first cable TV dates back to the late 1940s, when antennas were located at the highest point in a community to deliver TV to areas that had difficulty receiving over-the-air broadcasts (see CATV).
From TV to Internet to Telephony
Since the cable companies were already wired into millions of homes, they had great success selling Internet access to its subscribers, starting in the late 1990s. Unlike the telephone company's DSL service, Internet access via the cable infrastructure does not have distance limitations. Cable TV companies later added telephone service to offer the "triple play" (data, voice and video service). See cable Internet.
Many Analog and Digital Channels
Cable TV typically transmits 125 6 MHz channels using frequency division multiplexing (FDM) to its subscribers. Each channel can hold one analog TV program, three high-definition (HD) digital programs or 10 standard definition (SD) digital programs. The digital channels provide 40 Mbps of digital bandwidth, 38 of which is the actual payload.
The channels are also used for video-on-demand, Internet access and voice over IP (VoIP) telephone service. Upstream channels use from 0 to 50 MHz, while downstream channels use 50 MHz to 750 MHz. See FDM, CMTS and digital TV transition.