PRI (Primary Rate ISDN)

PRI is a 4-wire 1.544 megabits per second (DS1) local switching system port that uses the B8ZS line code and the ESF framing format. PRI is available in a twenty-three B channel plus one D channel (23B + D) configuration or a twenty-four B channel (24B) configuration. This service is very popular for mid-sized to enterprise customers because it allows 23 simultaneous voice calls over its 4-wire construction.