ISDN Telefonanschluss (Integrated Services Digital Network Telephone Connection) is a digital telephony service that allows for the transmission of voice, data, and video over a single telephone line. It was developed in the 1980s as a replacement for the analog telephone system and was widely used in businesses and homes before the advent of broadband internet.
ISDN offers a number of advantages over analog telephone lines, including higher data transmission speeds, better voice quality, and the ability to support multiple devices on a single line. It is also more reliable and secure than analog lines, making it a good choice for businesses that need to transmit sensitive data.