Primary Rate Interface ISDN (PRI-ISDN)

Definition of Primary Rate Interface ISDN (PRI-ISDN) in Network Encyclopedia.

What is Primary Rate Interface ISDN (PRI-ISDN)?

PRI-ISDN is a standard form of communication on Integrated Services Digital Network (ISDN) communication systems. Primary Rate Interface ISDN (PRI-ISDN) connections consist of 24 digital channels divided between 23 B channels and a single D channel.

The B channels carry the voice or data between the customer premises and the telco’s central office (CO), while the D channel is used for establishing connections and signaling.

PRI-ISDN is often referred to as 23B+D because of the channels that it uses.


The bandwidth of each B channel and of the single D channel is 64 Kbps, so the total bandwidth of PRI-ISDN is 1.544 Mbps, which is identical to that of a T1 circuit. By using the bonding protocol, the 23 B channels can be combined to form a single 1.472-Mbps data channel. The European version of PRI-ISDN uses 31 B channels and one D channel, providing the bandwidth of an E1 circuit.

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