ISDN BRI vs ISDN PRI: Understanding the Differences

This article clarifies the distinctions between ISDN BRI (Basic Rate Interface) and ISDN PRI (Primary Rate Interface). ISDN, or Integrated Services Digital Network, is designed to replace traditional analog local loop connections.

It allows computers to connect directly using digital lines, eliminating the need for a modem. It utilizes the same twisted-pair cables that were previously used for digital data transmission. The primary application of ISDN is high-speed internet access.

ISDN BRI: Basic Rate Interface

• This ISDN interface type uses a single twisted pair cable for signal transmission.
• ISDN BRI employs time-division multiplexing to manage 2 bearer channels (‘B’) for voice and 1 channel for data control (‘D’).
• Each B channel has a capacity of 64 Kbps, while the D channel has a capacity of 16 Kbps.
• B-channels handle all types of data, including voice, while the D-channel manages signaling and control functions (e.g., busy signals, dial tones).
• In ISDN BRI, one B channel is typically used for transmission and the other for receiving.
• It’s primarily used to provide a single connection to residential locations.

ISDN PRI: Primary Rate Interface

• The ISDN PRI interface uses 23 B channels and 1 D channel.
• Each B channel has a capacity of 64 Kbps, while the D channel has a capacity of 64 Kbps.
• This configuration results in a total capacity of 1.536 Mbps on the ISDN PRI interface.
• ISDN PRI is mainly used to provide connections to larger office buildings.
• It effectively creates a small PBX within the company.
• It’s a T1-compliant interface. For details on T1 frames, see T1 frame vs E1 frame.