Cable broadband is internet that reaches homes over the coaxial cable of a cable TV network, the same thick round wire that carries TV channels. In India, some local cable operators, the small businesses that run cable TV in a neighbourhood, sell broadband this way. The standard that carries the data is called DOCSIS.
A cable TV wire can carry a wide range of frequencies. The cable operator divides this range into channels, each a few megahertz wide. Most of these channels carry television channels, which the operator receives and compresses with video encoders before sending them out. Cable broadband uses some of the remaining channels to carry internet data instead of TV.
At the operator's main building, called the head end, a machine called the CMTS, or cable modem termination system, connects the cable network to the internet. Older CMTS machines were large boxes. Today, a CMTS often runs as software on ordinary servers. In each home, a cable modem turns the signal on the wire back into data. The modem is often combined with a Wi-Fi router, as a home gateway.
Usually, fibre runs from the head end to a node in each neighbourhood, and coaxial cable runs from the node to each home. This mixed design is called hybrid fibre-coaxial, or HFC. All the homes on one node share its capacity, as homes on a fibre splitter do.
Take, for example, a local cable operator in Madurai that serves 1,800 homes with TV. It wants to sell broadband without laying new cable to every door. It installs a CMTS at its head end and connects it to the internet through a larger provider. It then gives each new broadband customer a cable modem. A customer who pays for a 50 megabits-a-second plan gets internet over the same wire that brings their TV channels. The operator bills TV and broadband together, often through telecom billing software.
Cable broadband matters less in India than in some other countries. Here, many cable operators now lay fibre for broadband instead, using a passive optical network (PON), and use the coaxial cable only for TV. Cable broadband uses the existing wire, so it costs less to start. Fibre gives more speed and needs less maintenance. Some cable operators also sell addressable TV advertising over the same network, showing different ads to different homes. The other ways of reaching a home are described in fixed broadband access.