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Collaboration, Voice & AV · Foundational

Basic Rate Interface (BRI)

An ISDN interface with two 64 kbps B channels and one 16 kbps D channel, written 2B+D.

Definition

BRI was designed for small offices and residential ISDN, providing two bearer channels for voice or data plus a D channel for signaling, for 144 kbps of usable capacity. It uses Q.921 at Layer 2 and Q.931 for call control on the D channel. BRI is largely obsolete but still appears in some European deployments and on exam objectives about ISDN.

Example

A small branch in Europe uses an ISDN BRI for two simultaneous PSTN calls.

Exam tip

Do not confuse BRI (2B+D, 16 kbps D) with PRI, whose D channel is 64 kbps.

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