The Integrated Services Digital Network (ISDN)

Abstract

In 1972, the plenary assembly of the International Telegraph and Telephone Consultative Committee (CCITT) approved Recommendation G.711 for Pulse Code Modulation (PCM) of Voice Frequencies. This provided for a sampling rate of 8000 per second and 8-bit encoding/decoding with either A-law or μ-law companding (see Chapter 3). In 1980, the plenary assembly approved Recommendation G.705 which recognized that substantial agreement had been reached in studies of integrated digital networks (IDN) for telephony and that studies leading to an Integrated Services Digital Network (ISDN) were needed. Some conceptual principles to guide the studies provided for: the ISDN to be based upon and evolve from the telephony IDN by adding functions and features; a layered functional set of protocols; gradual transition over one or two decades; new services to be compatible with the 64-kb/s switched digital connections of the IDN; and arrangements during transition for the interworking of services on the ISDNs and services on other networks.