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integrated services digital network : FOLDOC | Integrated Services Digital Network (ISDN) A set of communications standards allowing a single wire or optical fibre to carry voice, digital network services and video. ISDN is intended to eventually replace the plain old telephone system. ISDN was first published as one of the 1984 ITU-T Red Book recommendations. The 1988 Blue Book recommendations added many new features. ISDN uses mostly existing Public Switched Telephone Network (PSTN) switches and wiring, upgraded so that the basic "call" is a 64 kilobits per second, all-digital end-to-end channel. Packet and frame modes are also provided in some places. There are different kinds of ISDN connection of varying bandwidth (see DS level): DS0 = 1 channel PCM at 64 kbps T1 or DS1 = 24 channels PCM at 1.54 Mbps T1C or DS1C = 48 channels PCM at 3.15 Mbps T2 or DS2 = 96 channels PCM at 6.31 Mbps T3 or DS3 = 672 channels PCM at 44.736 Mbps
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