ISDN is a standard in telecommunications. It has replaced the analogue telephone network in Germany. ISDN integrates not just telephone and fax but also video telephony and data transfer. ISDN can be used to transfer speech, text, graphics and other data, irrespective of the end device.
ISDN uses the S0 interface of a base connection to provide two base channels (B-channels), each with 64 kBit/s, plus a control channel (D-channel) with 16 kBit/s. All together the digital subscriber connection has a maximum communication speed of 144 kBit/s (2B + D). In both B-channels, two different utilities can be serviced simultaneously through a single line, at the transmission rate of 64 kBit/s.