Let’s focus on Plain Old Telephone Service (POTS) applications. The telephone analog frequency uses only a small proportion of the bandwidth on a line, i.e. up to 4 kilohertz (KHz). The maximum amount of data that any basic dial-up modem can transmit through a POTS system is 56 kilobytes per second (Kbps), therefore using this system to send data creates an absolute bottleneck.

The analog telephone frequency range has a limited bandwidth, so if data communication equipment is networked, only very small amounts of information can be transmitted and received over the phone line at any one time. A wide band of frequencies is necessary if this system is to operate efficiently to transmit information, whether it is voice, data or video, in a given amount of time.