Cable Modem Definition

A cable modem is a type of modem that can be used to connect a computer to a cable television network in order to take advantage of the unused capacity in such network and thereby provide a broadband (i.e., high speed) connection to the Internet.

A modem is an electronic device that encodes digital data on to an analog carrier signal (a process referred to as modulation), and also decodes modulated signals (demodulation). This enables computers' digital data to be carried over analog networks, such as cable TV lines and the conventional telephone network (sometimes referred to as the public switched telephone network or PSTN).

Whereas the typical cable television system only allows TV signals to be broadcast in one direction (i.e., to the home, office, etc.), cable modems allow information to be transmitted in both directions. Cable modems connect to coaxial cable, which features a much greater bandwidth (i.e., frequency range and thus data carrying capacity) and is used to transport television signals. This contrasts with dial-up modems, which connect to the same twisted pair copper wire cable that is used to connect telephones.

Cable modems thus make possible data transfer rates of at least 6Mbps (million bits per second) downstream (i.e., reception) and 768Kbps (thousand bits per second) upstream (i.e., transmission) under optimal conditions (e.g., low network congestion). The maximum for conventional dial-up connections to the PSTN is a mere 56Kbps.

As is the case with dial-up modems, both internal and external cable modems are available, each with their own advantages and disadvantages. External cable modems can be connected to the user's choice of Ethernet and USB (universal serial bus) connectors.

Created December 3, 2005.
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