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cable modem - technical definition

A modem designed to support high speed data communications over hybrid fiber/coax (HFC) CATV networks. Cable modems are positioned at the customers' premises and in a cable modem termination system (CMTS) at the service provider's headend. The initial Data over Cable Service Interface Specification (DOCSIS), released in 1997, standardized cable modems. Continuing research and development efforts directed at cable modems and related CATV network standards are largely the responsibility of CableLabs. See also CableLabs, CATV, CMTS, DOCSIS, HFC, and modem.

See cable modem in Webster''s New World Hacker Dictionary

A technology for connecting users to the Internet through the TV-cable network and has the advantage of high-speed bandwidth 10Â–50 times as high (up to 5 megabits per second) as dial-up modems, which have 56 kilobits per second and use the telephone networks. TV-cable providers have to upgrade their network infrastructure to offer the service, whereas the dial-up modems need just a telephone line for connectivity. An alternative to the usage of cable-modems is DSL (Digital Subscription Line). DSL makes use of existing telephony lines and achieves approximately the same transmission speeds as cable modems.

See Also: DSL Modem; Network.

See cable modem in Computer

A device used to connect a computer to a cable TV service for Internet access. Compared to analog dial-up, cable Internet dramatically increases the bandwidth between the user's computer and the Internet. Download speeds have reached 16 Mbps and beyond, but the connection is asynchronous. In order to prevent users with lower-cost cable access from hosting high-traffic Web servers, the upload speed is approximately 10 times slower. Cable operators also routinely change IP addresses assigned to users to prevent Web hosting (see DDNS).

Connect Via Ethernet
Cable modems connect to the computer via an Ethernet port, which is an always-on connection. Ethernet is a shared medium, and the individual user's speed will vary depending on how many customers are sending or receiving data on that cable segment at the same time. For example, when the kids come home from school around 3pm, many cable users experience a corresponding slowdown. See DOCSIS, cable Internet, Internet appliance and MSN TV.

A Cable Modem System

Internet packets are combined with standard TV programming in a cable modem system. The cable modem termination system (CMTS) is responsible for packet to RF conversion, routing, bridging, filtering and traffic shaping (see CMTS).

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