(PRI) A type of ISDN connection. In North America and Japan, this consists of 24 channels, usually divided into 23 B channels and 1 D channel, and runs over the same physical interface as T1. Elsewhere the PRI has 31 user channels, usually divided into 30 B channels and 1 D channel and is based on the E1 interface.

PRI is typically used for connections such as one between a PBX (private branch exchange, a telephone exchange operated by the customer of a telephone company) and a CO (central office, of the telephone company) or IXC (inter exchange carrier, a long distance telephone company).