What is ISDN?

ISDN (Integrated Services Digital Network) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network (PSTN). It was commonly used for faster internet access compared to dial-up, as well as for videoconferencing and PBX systems, but has largely been replaced by broadband technologies like DSL, cable internet, and fiber optics.