A cable modem is a type of modem used to allow computer systems and networks to communicate over cable television infrastructure networks. These networks use coaxial cable media currently defined by the rg6 cable standard in the United States. RG6 cable is usually triple or quadruple shielded, is generally available in 500 or 1000 foot lengths, and has a sweep test range of 1Ghz (1000Mhz). Belden makes specialized and high end coaxial cable that far surpasses the normal standards, including cables that sweep test to 3Ghz or even 4.5Ghz.
Cable modems are generally used for broadband based Internet access, and has downlink speeds of up to 8Mbit, and commonly uses uplink speeds of 768Kbits or more.
Cable modems are an "always-on" technology that does not require dialing, or the use of phone lines or the telephone system.
Most cable companies providing Internet access use DOCSIS or the Data Over Cable Service Interface Specification as their overlaying protocol for communication.