Frequency division multiplexing is used to put several channels on the same cable simultaneously. To understand frequency division multiplexing, think of the cable as a highway. It is the difference between a higher and a lower frequency- the greater the spread between the upper and lower frequency, the more information can be transported. Just as cars travelling in different lanes of a highway do not collide, information occupying one frequency band or channel on a cable does not interfere with information on another band. Thus, frequency division multiplexing sends its different types of information at unique frequencies.
Digital signals are discrete-one or zero.
Analog is continuous, like a wave. To reconcile this difference, digital computer data must be converted into analog form for transmission over a broadband cable. The conversion device is called a broadband modem. The root of the tree is the headend, or central retransmission facility. The trunk cable is attached to this root.