Cable modem

Cable Modems are devices used to transfer data, typically internet services, generally over cable television infrastructure. The overall system where an internet service provider uses these devices is referred to as cable internet or simply cable. The modem part of a cable modem device is used to transfer digital information over an analogue network. Many cable modems have additional advanced functions such as a routing, virtual private networking and firewalling.

Cable modems were primarily developed to bring high speed internet access to consumers. They can take advantage of the existing high bandwidth available of the cable television network that has been rolled out to the majority of urban/city dwelling people in many developed countries. Prior to this, relatively slow dial-up access to the internet via the public switched telephone network was the norm.

Users in one locality share the available bandwidth provided by the single coaxial cable in the neighborhood. Therefore depending on the usage of the service, known as contention, internet connection speeds can vary from blistering fast to dead slow. Note, however that any measurements of internet speed are fraught with uncertainty as bottlenecks can occur anywhere outside a users or ISPs control. In any case, along with ADSL, cable internet is known as broadband because of the higher speeds.

The most common standard used is DOCSIS[?] (Data Over Cable Service Interface Specification).

There has been a number of cable modem manufacturers such as Nortel, Ericcson, 3Com, Cisco etc.