Broadband Integrated Services Digital Network
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In the 1970s the telecommunications industry conceived that digital services would follow much the same pattern as voice services, and conceived a grandiose vision of end-to-end circuit switched services, known as the Broadband Integrated Services Digital Network (B-ISDN). This was conceived as a logical extension of the end-to-end circuit switched data service, ISDN.
The technology for B-ISDN was going to be Asynchronous Transfer Mode (ATM), which was intended to carry both synchronous voice and asynchronous data services on the same transport.
The B-ISDN vision has been overtaken by the disruptive technology of the Internet. The ATM technology survives as a low-level layer in most DSL technologies.
Over fibre optic lines, the maximum Data bandwidth is 1.5 Megabits and point-to-point protocol is typically used to carry data over the B channels.