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Cable modem

A cable television system (CATV) distributes broadcast signals from a headend, which is a center of a CATV provider, to subscribers via trunk lines and branch lines, which are configured in a tree structure or in a star structure. The trunk lines and branch lines are used for transmission of broadband broadcast signals, and are implemented by using a coaxial cable or an optical fiber cable. With the explosive growth of the Internet, many customers have desired to use the larger bandwidth of a cable television network to connect to the Internet and other computer networks. In response to the bandwidth limitations of general modem connections, the industry is now turning to alternative methods of connecting to the Internet. A popular alternative to the general modem-type connection is the cable modem (CM) technology which utilizes the cable television infrastructure to transmit and receive Internet related data from a home-computing source. As an alternative to using telephone lines, the Internet can be accessed through coaxial cables using a cable modem. Coaxial cables provide greater bandwidth than home telephone lines and are widely available to existing cable television subscribers. The greater bandwidth also enables new applications such as telephony-over-cable that are not necessarily associated with the Internet. Cable modems can achieve data-transfer rates of up to 40 Mbits/s by connecting directly to coaxial lines as opposed to dial-in modems, that use twisted-pair copper telephone lines. A cable modem receives and transmits data in the form of digitally encoded radio frequency transmissions, which typically travel to and from the cable modem on coaxial cable. In a typical configuration, a personal computer is equipped with a cable modem that interfaces with an existing coaxial cable used to provide cable television service to the home. This coaxial cable is then used to transmit both Internet and television signals to the home. Cable modem systems typically include one or more head ends or cable modem termination system (CMTS) devices that engage in bidirectional communication with the various subscribers' cable modems. Both the cable modems and the CMTS devices include modulators to transmit data, as well as demodulators to receive and demodulate the incoming data. A cable modem network consists of a number of cable modems in subscriber homes, a cable modem headend system, and a coaxial or hybrid-fiber/coax communication link between the headend and the subscriber modems. Unlike traditional dial modems, cable modems transmit and receive digital signals at radio frequencies. A cable modem is equipped on its back with a radio-frequency (RF) coaxial connector for connection to a CATV trunk line, an Ethernet connector or jack for connection to a PC or the like, a universal serial bus (USB) connector or jack, a reset switch to return the modem to its initial state, and a power supply connector to receive electric power.

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