What is the difference between ISDN and regular analog modem services?

All modems transmitting at 2,400 baud through the "fast" 56.7 kilo-bits per second (Kbs) are analog modems. These modems take the digital information coming from your computer and translate it into an analog signal before sending it out over a standard telephone line. At the other end, another analog modem has to translate the analog signal back into a digital stream of information. This method allows only one data stream at a time to pass over the telephone line. As a result, the line cannot hold a telephone conversation and an online modem connection at the same time.

Moving to ISDN phone service is kind of like switching from vinyl records to CDs. Even at its most basic, ISDN allows your telecom connection to carry as many as three different "conversations" at the same time with the same copper wires you currently use for a standard telephone connection. This is accomplished by using multiple channels of information, increasing the available bandwidth from the 4 kHz provided by standard telephone lines (voice lines) to two channels carrying 64,000 bits per second and a third data and control channel handling 16Kbs.

ISDN has become less common in recent years with the advent of affordable broadband internet connections, such ADSL and cable modem connections, which are significantly faster than ISDN while remaining comparable in price in many areas.