User's Manual

TurboComm EC110 User’ s Manual
Page 5
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 10BaseT Ethernet connection used by TurboComm 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 TurboComm Cable Modem to work.
What is DOCSIS?
Data Over Cable Service Interface Specifications. DOCSIS defines interface
requirements for cable modems involved in high-speed data distribution over a cable television
network.
On November 17, 1997, Cable Television Laboratories, Inc. (Cable Labs) and its
members established a formal path of certification for cable modem equipment
suppliers to obtain an "interoperability seal" for their products based on the DOCSIS specification. This
certification process provides cable modem equipment suppliers with a fast, market-oriented method
for attaining cable industry acknowledgment of compliance with DOCSIS.
The seal is meant to provide the purchaser with a way to be confident that the modem equipment to be