ISDN (Integrated Services Digital Network) is a digital telecommunications network that allows for the simultaneous transmission of voice, data, and video over a single line. ISDN uses a circuit-switched network, which means that a dedicated connection is established between the two communicating devices for the duration of the call.
ISDN offers a number of benefits over traditional analog phone lines, including higher quality voice transmission, faster data speeds, and the ability to support multiple devices on a single line. ISDN was first developed in the 1980s, and it has been widely adopted by businesses and governments around the world. However, the advent of VoIP (Voice over IP) technology has led to a decline in the use of ISDN in recent years.