A worldwide digital communications network evolving from existing telephone services. Its goal is to replace current telephone lines that require DA conversions with totally digital switching and transmission facilities capable of carrying a variety of data—from voice to computer transmissions, music, and video.

The ISDN is built on two main types of communications channels: a B channel, which carries data at 64 Kb/s, and a D channel, which carries control information at either 16 or 64 Kb/s. Computers and other devices connect ISDN lines through simple, standardised interfaces. When fully implemented (possibly around the year 2000), the ISDN is expected to provide users with faster, more extensive communications services.