5.5 ISDN

5.5 ISDN

ISDN, the Integrated Services Digital Network, is an extension of the digital telephone network to the consumer, providing two 64 Kb/s digital channels that can be connected to ISDN terminals anywhere in the world by dialling. Since the total usable capacity of an ISDN ˜B' connection is only 128 Kb/s it is not possible to carry linear PCM data at normal audio resolutions over such a link, but it is possible to carry moderately high quality stereo audio at this rate using a data reduction system such as MPEG Layer 3 ⁸ , or to achieve higher rates by combining more than one ISDN link to obtain data rates of, say, 256 or 384Kb/s ⁹ . ˜Broadband ISDN', on the other hand, is capable of much higher data rates than a simple ˜B' channel connection and is in fact another name for ATM networking, described in the previous section.