Toshiba PCX1100U - Manual (Page 8)

6
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, high and low electrical voltage levels represent digital signals. 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 has 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, an encryption/decryption device, an SNMP agent, an
Ethernet hub and USB interface. 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 and USB connection used in this Cable
Modem
are emerging as the most popular means of connecting a cable modem.
The new DOCSIS standard may change this in the future. But for now, a
10BASE-T Ethernet or USB must be ready in your computer for the Cable Modem
to work.