Overview; How Does A Cable Modem Work; How Does A Cable Modem Connect To A Computer - Toshiba PCX1000 Owner's Manual

Docsis cable modem
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Overview

The modem provides you with high-speed data communications over the television
cable network by following the widely accepted DOCSIS/MCNS standards being
developed by the Multimedia Cable Network System (MCNS) consortium. Those
standards offer a combination of high performance and interoperability among many of
the cable system operators in North America.

How does a cable modem work?

As you know, digital signals are represented by high and low electrical voltage levels.
And how fast these levels can switch and still be transmitted is determined by the
"bandwidth" of the transmission system. The pair of wires used in a telephone
connection have greatly limited bandwidth, because of their electrical characteristics.
So what we do is connect a device called a modem between the computer output and
the phone line. The modem generates an electrical wave whose strength and phase
change in step with the highs and lows of the computer's digital output. It's because of
the "smoothness" of the resultant signal that a higher data rate can be transmitted.
A cable modem MOdulates and DEModulates electrical signals in the same sense that
the telephone modem does. However, since coaxial cable can carry much higher wave
frequencies, cable modems are far more sophisticated. Their internals can include a
tuner, a bridge, a router, an encryption/decryption device, an SNMP agent and an
Ethernet hub. Furthermore, none of the activity caused by these circuits and codes
disturbs your regular cable TV reception.

How does a cable modem connect to a computer?

The 10BASE-T Ethernet connection used in this Cable Modem is emerging as the most
popular. This connection has been used for years to allow business computers to talk
to each other in a LAN (Local Area Network).
The new DOCSIS standard may change this in the future. But for now, an Ethernet
card must be installed in your computer for the Cable Modem to work.
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