ISDN (short for Integrated Service Digital Network) is a circuit-switched telephone network system that allows both voice and data services to be delivered over digital lines simultaneously. It was launched by BT in 1986 as a means to migrate outdated landline technology to digital.
When it launched, businesses got excited about ISDN because it could support both an analogue phone line and early video-conferencing systems. At the time, it also offered the fastest internet access available (128 kbps).
The faster speeds and better connections that ISDN allowed meant data could be sent quicker and with little to no distortion, providing a better overall experience than previous antiquated systems.
With the introduction of new broadband internet access connections like DSL, WAN and Cable Modems, ISDN itself is now pretty much an outdated legacy system. Despite this, it’s often used as a backup phone system in the event a main line fails.