Integrated Services Digital Network (ISDN) is a set of communication standards for the simultaneous digital transmission of voice, video, data, and other network services over the digitalized circuits of the public switched telephone network .

• Developed at Bell Labs starting in 1980
• By the time the standard was released faster networking systems were available
• Never was widely adopted
• ISDN was largely replaced by digital subscriber line (DSL)

Source: https://en.wikipedia.org/wiki/Integrated_Services_Digital_Network