- (telecommunications, initialism) Integrated services digital network.
- (chemistry, initialism) Isosorbide dinitrate.
isdn - Computer Definition
A set of ITU-T Recommendations describing a set of interfaces for access to a digital public switched telephone network (PSTN) intended to provide ubiquitous access to a wide range of services, including voice, data, video, and multimedia.The I series ISDN Recommendations map into the OSI Reference Model at the bottom three layers:
(Integrated Services Digital Network) An international standard for switched, digital dial-up telephone service for voice and data. Analog telephones and fax machines are used over ISDN lines, but their signals are converted into digital by the ISDN terminal adapter (see below). Although announced in the early 1980s, it took more than a decade before ISDN became widely available. It enjoyed a surge of growth in the early days of the Internet, because it provided the only higher-speed alternative to analog modems in many areas. Still working in many behind-the-scenes applications, ISDN is rarely used for Internet access today. Channels ISDN uses 64 Kbps "B" (bearer) channels to carry voice and data. A separate "D" (delta) channel is used for control. The D channel signals the carrier's voice switch to make calls, put them on hold and activate features such as conference calling and call forwarding. It also receives caller ID data. Because the D channel connects directly to the telephone system's SS7 signaling network, ISDN calls are dialed much faster than regular telephone calls. Basic Service (BRI) ISDN BRI (Basic Rate Interface) uses one wire pair to carry two 64 Kbps B channels and one 16 Kbps D channel (2B+D). Both B channels are often "bonded" into one, providing a total data rate of 128 Kbps. Higher Capacity (PRI) ISDN PRI (Primary Rate Interface) uses four wire pairs to provide 23 B channels and one 64 Kbps D channel (23B+D). A PRI line is equivalent to a 24-channel T1 line. Bonding channels is common; for example, six channels provide 384 Kbps for high-quality videoconferencing. In Europe, PRI includes 30 B channels and one D channel, equivalent to an E1 line. See SS7 and T1.