Integrated Services Digital Network is a set of digital transmission protocols defined by the international standards body for telecommunications, the ITU-T (formerly called the CCITT). These protocols are accepted as standards by virtually every telecommunications carrier all over the world.

ISDN complements the traditional telephone system so that a single pair of telephone wires is capable of carrying voice and data simultaneously. It is a fully digital network where all devices and applications present themselves in a digital form.

The essential difference between ISDN and the conventional telephone system is that it is digital not analogue (Click here to understand more about analogue.). Information travels as bits rather than as waves. In addition, it also allows multiple streams of these bits to occupy the same connection, providing the user with greater versatility of services.

What are the applications for ISDN?

The Integrated Services Digital Network uses the twisted-pair copper telephone line that would traditionally carry only one voice connection. ISDN can carry more than one connection over this wire at the same time, and at greater speed. Applications include telecommuting; simultaneous voice, fax, data and e-mail; inexpensive videoconferencing; remote broadcasting and high quality audio transmission.