Integrated Services Digital Network - ISDN
An integrated services digital network (ISDN) is a structured all digital telephone network system that was developed to replace (upgrade) existing analog telephone networks. The ISDN network supports advanced telecommunications services and defined universal standard interfaces that are used in wireless and wired communications systems. ISDN provides several communication channels to customers via local loop lines through a standardized digital transmission line. ISDN is provided in two interface formats: basic rate (primarily for consumers) and high-speed rate (primarily for businesses). The basic rate interface (BRI) is 144 kbps and is divided into three digital channels called 2B + D. The primary rate interface (PRI) is 1.54 Mbps and is divided into 23B + D for North America and 2.048 Mbps and is divided into 30B + 2D for the rest of the world. The digital channels for the BRI are carried over a single, unshielded, twisted pair of copper wires and the PRI is normally carried on (2) twisted pairs of copper wire.