Integrated Services Digital Network - A digital transport and signaling system that conveys both user traffic and control signaling across the same physical channel. This type of technology is classified as a physical in-band/logical out-of-band system. In it's most typical configuration (called 'BRI' or 'Basic Rate Interface') it has two channels capable of 64 Kbit/s data traffic. Each of these can be configured for normal data or digitized voice as a phone line. There is also one signalling channel that carries call progress information at 16 Kbit/s. ISDN is flesible and can be configured in many other ways, but most people think of it as having the capabilities described. ISDN is loosing popularity to DSL services.