(
Primary
Rate
Interface) A digital transmission service for businesses from the telephone company. Widely used to connect a company PBX to the public switched telephone network (PSTN), PRI is an ISDN dial-up service that is based on the T1 line in North America (24 channels) and E1 in Europe (32 channels). Typically using four wire pairs, PRI/T1 provides 23 voice channels and one signaling channel, and PRI/E1 delivers 30 voice channels and two signaling channels. See
ISDN,
T1 and
E1.