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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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