Basic Rate Interface

Basic Rate Interface (BRI, 2B+D, 2B1D) or Basic Rate Access is an Integrated Services Digital Network (ISDN) configuration intended primarily for use in subscriber lines similar to those that have long been used for voice-grade telephone service.

As such, an ISDN BRI connection can use the existing telephone infrastructure at a business.

The BRI ISDN service is commonly installed for residential or small business service (ISDN PABX) in many countries.

In contrast to the BRI, the Primary Rate Interface (PRI) configuration provides more B channels and operates at a higher bit rate.

The BRI is split in two sections: a) in-house cabling (S/T reference point or S-bus) from the ISDN terminal up to the network termination 1 (NT1) and b) transmission from the NT1 to the central office (U reference point).