ISDN telephony, short for Integrated Services Digital Network, is a digital telecommunications technology that enables the transmission of voice, data, and video over digital circuits.
ISDN offers several advantages over analog telephony, including higher quality, more reliability, and increased bandwidth. It was first introduced in the early 1980s and was widely used for business communications. However, with the advent of Voice over IP (VoIP) and other digital technologies, ISDN has become less common.