Ericsson HM200c/HM201c User Manual

The cable that provides service to your PipeRider cable modem is connected to the same cable network system

that brings cable TV service to your home.  A simplified version of the cable system is depicted below.  Click on

the diagram for a description of each of the main system components.

 

The Headend can be thought of as the control center of the system. The Cable TV (CATV) equipment receives

signals from sources such as satellite and broadcast transmissions. These signals are processed --- amplified,

converted, combined --- and then transmitted to your home. In addition to receiving TV signals, the Headend

equipment includes a computer, known as the Headend Router, that controls operations between the Headend

equipment and the Internet.
The Cable Modem Termination System (CMTS) is a major component of the Headend. The CMTS interfaces to the

cable network, the backbone data network, and several support systems. It controls the configuration,

registration, and media access of all the PipeRider cable modems under its control, and determines who gets to

transmit when and for how long. The CMTS can talk to all the cable modems, but the cable modems can only talk

to the CMTS. Therefore, if two cable modems need to talk to each other, the CMTS will relay the messages.

A main "trunk" cable carries the signals out from the service provider building. The trunk cable then branches into

smaller diameter "feeder" cables, which lead out into the different geographic areas serviced by the provider. An

even smaller "drop" cable connects the feeder cable to the customer's home, where it is then split into two cables:

one that goes to the TV (if the customer subscribes to cable TV), and another that connects directly into the

PipeRider cable modem.
Many cable networks are Hybrid Fiber-Coax. This means that signals run in fiber-optical cables from the Headend

through the trunk cable, and as the cable branches out, the signal is transferred to coaxial cables. This branching

architecture is the most efficient method of transmitting the video and data signals from a Headend to multiple

customers.

The PipeRider cable modem performs many functions.  It operates as a modem, a duplex tuner, an

encryption/decryption device, a server, a bridge, a router, and more.
An important component of the cable modem is the Media Access Control (MAC) mechanism. The MAC runs the

protocol and is positioned between the receive and transmit paths. In coordination with the CMTS, the MAC plays

a major role in controlling the sharing of media. For example, the MAC controls ranging, assigns frequencies, and

allocates time slots.
The PipeRider cable modem tunes to the channel that has been dedicated for data transfer. It receives the data

from the service provider in the form of radio frequency (RF) signals, and translates the data to USB or Ethernet

signals that can be understood by your computer. The cable modem exchanges data in two slightly different

manners, depending upon whether the modem is transmitting or receiving data. One spectrum of signal

frequencies is assigned for the signals that move from the Headend towards the user (downstream), and another

spectrum of signal frequencies is assigned for the signals that move from the user towards the Headend

(upstream). Typically, higher frequencies flow downstream and lower frequencies flow upstream.