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Definition: cable modem


A device used to connect one or more computers to a cable company's Internet service. The same coaxial cable coming into the house or office also provides TV and voice over IP (VoIP) service.

Compared to analog dial-up, cable Internet dramatically increased the bandwidth between the user's computer and the Internet (see broadband). In order to prevent residential customers from hosting high-traffic Web servers, the cable's upload speed is generally much slower than the download speed, and the cable company may routinely change the IP address assigned to the modem to prevent Web hosting (see DDNS).

Connect Via Ethernet or USB
Cable modems typically connect to a computer or router via Ethernet; however, some cable modems connect to one computer via USB. In addition, the cable modem is often combined with the router (see cable/DSL gateway).

A Shared Service
Cable Internet speeds vary depending on how many customers are sending and receiving data on that cable segment at the same time. For example, when kids come home from school in the afternoon, users in the neighborhood may experience slower speeds. See DOCSIS and Internet appliance.




A Cable Modem System
At the cable company plant, Internet packets are combined with standard TV programming. See CMTS.