Basic Rate Interface

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Basic Rate Interface
The entry level interface to ISDN is the Basic Rate Interface (BRI), a 144 kbit/s service delivered over a pair of standard telephone copper wires. The 144 kbit/s rate is broken down into two 64 kbit/s bearer channels (‘B’ channels) and one 16 kbit/s signaling channel (‘D’ channel or Delta channel).
BRI is sometimes referred to as 2B+D
The Interface specifies three different network interfaces:The U interface is a two-wire interface between the exchange and the Network Terminating Unit which is usually the demarcation point in non-North American networks.
· The T interface is a serial interface between a computing device and a Terminal Adapter, which is the digital equivalent of a modem.
· The S interface is a four-wire bus that ISDN consumer devices plug into; the S & T reference points are commonly implemented as a single interface labeled ‘S/T’ on an NT1
· The R interface defines the point between a non-ISDN device and a terminal adapter (TA) which provides translation to and from such a device.
BRI-ISDN is very popular in Europe but is much less common in North America.

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