A category of communications where bandwidth is equivalent to that of a telephone line obtained through the public telephone network. The maximum potential bandwidth of a voice-grade channel is approximately 20 kilohertz; however, most voice grade channels in a transmission facility are usually spaced 4,000 hertz apart, and not all of that bandwidth is generally available to a user due to the presence of noise-limiting loading coils. The telephone network itself is usually defined in terms of channels, with frequencies from 300 to 3,400 hertz.