ISDN - Integrated Services Digital Network
Integrated Services Digital Network is a communication standard that allows transmission of voice, data, and video over the same line or channel. The channel could be the traditional public switched telephone network (PSTN).
Two type of channels are used for ISDN: B Channel or bearer channel that supports a speed of 64 kbit/s, and D channel or data channel which is of 16 kbit/s. Based on these channels, the interfaces of the Integrated Services Digital Network is defined:-
Basic Rate Interface (BRI)
The Basic Rate Interface provides a data rate of 128 kbit/s over a pair of standard telephone copper wires. It uses a pair of B channel and a single D channel, i.e. 2B+D. to achieve this rate.
Primary Rate Interface (PRI)
The Primary Rate Interface provides a data rate of 1544 kbit/s using 23 'B' channels and a single 'D' channel, i.e. 23B+D. However, in Europe and Australia the standard provides data rate of 2048 kbit/s using 30 'B' channels and a single 'D' channel, i.e. 30B+D.