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Acronym for Integrated Services Digital Network. It is a set of standards defining a digital, synchronous subscriber access for voice and data to screenshot.png a telephone network. It defines the use of 64kbps bearer channels to transport data (such as voice). Actual interfaces can (and do) provide more than one bearer channel (usually 2 (BRI) or 24/30 (PRI)) refered to as B-channel which can be aggregated for improved bandwidth. For call setup/tear down, a call signaling protocol is used (Q.931 and its derivates, e.g. DSS1 or QSIG) is used between the terminal and the central office (sometimes also referred to as local exchange) on a dedicated extra channel known as D-channel. A basic rate interface (BRI) hence is often referred to as 2B+D.

From a VoIP point of view, ISDN is mostly seen as a trunk line interface connecting the VoIP system to the existing world wide telephony network. ISDN's data transmission capabilities are rarely, if ever, used.

See wikipedia.ico Integrated Services Digital Network, although some of the information in there is rather questionable.

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