Internet Access Guide : Cable Modem

Picture: Internet access over Cable TV network
A cable modem communicates with the corresponding modem at the cable operator site (Headend).

In Internet access using cable modem, data (Internet) signal is delivered through HFC infrastructure which consists of fiber optic cables from a cable TV operator site or Head End down to a neighborhood hub and a coaxial cable from the hub to each subscriber house. At a subscriber house, a coax splitter is used to split the drop coaxial cable into several coaxial cables, typically one is allocated for Internet connection and the rest for cable TV delivery. Internet signal occupies a separate channel in the coaxial cable spectrum so it doesn't disturb the cable TV channels.

A cable modem at a subscriber site communicates with the corresponding modem at the CMTS over CATV network during an Internet connection. The communication follows DOCSIS (Data over Cable Modem Service Interface Specification) standard. Cable Modem Termination System (CMTS) at the Head End contains all modems that terminate connections from all subscribers' cable modems.

Internet access over cable TV network is delivered through a medium (coax) which is  shared by all subscribers within the coverage of a neighborhood hub. The maximum shared data rate is 38 Mbps downstream and 30 Mbps upstream. Real world performance depends on how many people within a neighborhood connect to the Internet at the same time, the connection to backbone network, and Internet traffic load. However most operators offer minimum downstream and upstream rates during peak hours.