Primary Rate Interface = primary access to the ISDN.

Connection to an ISDN network giving a subscriber-usable data rate of 1,984 kbit/s: 30 B channels of 64 kbit/s for transmission and one D channel of 64 kbit/s for signalling. The interface is called S2 or T2 , depending on whether you're on the terminal side or the public access side.

Not to be confused with BRI (Basic Rate Interface = basic access to the ISDN)