Figure 3-1 shows a schematic of a cable system that is not upgraded with fiber. Video programming for cable systems is obtained by satellite or microwave at places called head ends. Head ends have facilities to do the following:
Receive programming (for example, from NBC, CBS, and cable networks such as MTV and ESPN)
Convert each channel to the channel frequency desired, scramble channels as needed (for the premium channels)
Combine all the frequencies onto a single, broadband analog channel (frequency division multiplexing)
Broadcast the combined analog stream downstream to subscribers
Downstream traffic is also referred to as forwardtraffic. As of December 1996, there were 11,660 cable head ends in the United States.