Integrated Services Digital Network (ISDN)

Integrated Services Digital Network or Isolated Subscriber Digital Network (ISDN), originally "Integriertes Sprach- und Datennetz" (German for "Integrated Speech and Data Net"), is a circuit-switched telephone network system, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in better voice quality than an analog phone.

It offers circuit-switched connections (for either voice or data) in increments of 64 kbit/s. Another major use case is Internet access, where ISDN typically provides a maximum of 128 kbit/s (which can be considered to be broadband speed, since it exceeds the narrow band speeds of 56k telephone lines). More broadly, ISDN is a set of protocols for establishing and breaking circuit switched connections, and for advanced call features for the user. It was introduced in the late 1980s.

In a video conference, ISDN provides simultaneous voice, video, and text transmission between individual desktop videoconferencing systems and group (room) videoconferencing systems.