ISDN (Integrated Services Digital Network)

This is an evolution of the traditional telephone line in which the signal is already in digital form and so requires no modulation and demodulation. In order to connect up over such a line the user needs a special expansion card (ISDN adapter, improperly called an ISDN modem). Such a line, which may be requested from the telephone service provider and requires installation of a special device on the traditional telephone line, permits obtaining a bandwidth of 128 kbps subdivided into two 64 kbps channels. The dual channel and the wider bandwidth make it possible to manage a greater flow of information (e.g., audio / video) simultaneously with normal telephone services (voice and fax).

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