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How Cable
Internet Works
Historically Internet access was made
possible using Telephone line as the
medium of transfer, using a dial-up
modem. As the demand for faster Internet
access grew, newer technologies evolved
such as Internet access via the Cable
Television network.
For Cable Internet access on PC, a
Cable Modem is required at user's end. A
cable modem is an external device that
connects to the computer to provide
high-speed data access via cable TV
networks. A Cable Modem sends and
receives data to and from the Internet
by using the existing coaxial cable
network.
The modem translates cable signals
the same way a telephone modem
translates signals from a telephone
line. Cable modems translate radio
frequency (RF) signals to and from the
cable plant into Internet Protocol (IP),
the communications protocol spoken by
all computers connected to the Internet.
A cable modem connects to a computer
through a device called an Ethernet card
(Network Interface Card). This card
provides connectivity between the cable
and the computer and interprets the
signaling from the cable modem so that
the computer's software can display it
correctly.
Cable TV Networks are high band-with
networks i.e. 550 to 750 MHz by their
very nature of design. These networks
were traditionally built as one way
networks carrying 60-100 Cable TV
channels downstream i.e. from Headend to
the Subscriber. Internet delivery over
Cable TV however requires a two-way
network since information of selected
website, etc. has to be transmitted to
the Headend, from where it would be
directed to the website of interest.
Higher frequencies flow toward the
subscriber and the lower frequencies go
in the other direction.
Hence setting up of a robust two-way
Cable TV network is the first requisite
before deploying Cable Modems on a Cable
TV network.This is done by upgrades to
the amplifiers in the cable distribution
network etc.
The Internet signals are in the
digital domain and these need to be
interfaced to the Analog CATV world.
This interface is termed Cable Modem
Termination System (CMTS) and typically
serves 2000 - 3000 Cable Modems and is
connected to a high-speed data link. A
typical CMTS consists of an Input
interface, Router, Cable Modem card and
a powerful Microprocessor.
The CMTS resides at the ISP POP,
which receives high bandwidth data from
the ISP network center as well as Cable
TV signal from the Cable TV Head-end.
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