ISDN, or Integrated Services Digital Network, is a digital telecommunications technology that allows for the simultaneous transmission of voice, data, and video over a single digital line. ISDN was developed in the 1980s as a replacement for analog telephone lines, and it offers a number of advantages over analog, including higher quality voice and data transmission, faster speeds, and the ability to support a wider range of services.
ISDN is still used in some areas today, but it has been largely replaced by newer technologies such as broadband and fiber optics. However, it remains an important technology for businesses and organizations that require high-quality and reliable voice and data communications.