High Quality Content by WIKIPEDIA articles! The primary Rate Interface (PRI) is a standardized telecommunications service level within the Integrated Services Digital Network (ISDN) specification for carrying multiple DS0 voice and data transmissions between a network and a user. PRI is the standard for providing telecommunication services to offices. It is based on the T-carrier (T1) line in the US, and the E-carrier (E1) line in Europe. The T1 line consists of 24 channels, while an E1 has 32. PRI provides a varying number of channels depending on the standards in the country of implementation. In North America and Japan it consists of 23xB (B channels) and 1xD (D channel) (23 64-kbit/s digital channels + 1 64-kbit/s signaling/control channel) on a T1 (1.544 Mbit/s). In Europe and Australia it is 30xB + 1xD on an E1 2.048 Mbps. One timeslot on the E1 is used for synchronization purposes and is not considered to be a B or D channel.

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