For some years, ISDN has been the technology of choice for voice sessions and remote radio broadcasts. ISDN stands for Integrated Services Digital Network. It is a set of communication standards for transmission on the traditional copper lines of the Public Switched Telephone (PSTN)Network.

It is capable of transmitting voice as well as data using a digital line. You can make phone calls, video calls, transmit data, and other network services over the circuits of the traditional phone lines.

How does ISDN work?

ISDN splits the traditional copper telephone line into multiple channels that operate concurrently on a single copper line.

  • A B channel, or Bearer channel, is used for voice and user data.
  • A D channel, or Delta channel, is a combination of data, packet networking, control, and signaling.

B channel transmits the signal in a circuit-switch network, whereas the D channel transmits data with the help of packets. Each B channel has a capacity of 64 Kbps, and each D channel comes with a capacity of 16 Kbps. Combined, these channels help ISDN control the transmission of information.

ISDN BRI And ISDN PRI are the two types of ISDN services. Both PRI and BRI ISDN use B channels for sending data and D channels for other forms of communication. The difference lies in the number of channels they use to accomplish this.

What is ISDN BRI?

ISDN BRI, or Basic Rate Interface, uses only two B channels and one D channel. BRI functions by using a twisted pair of lines for transmission signals. The technology uses time multiplexing. Typically, one of the B channels functions as a transmission line and the other as a receiving line.

What is ISDN PRI?

ISDN PRI, or Primary Rate Interface, is designed to support up to 30 B channels and one D channel. PRI implementations vary in the number of channels depending on location.

What is ISDN PRI?

There are two types of PRI called T- carrier, and E-carrier. In the US and Japan, PRI implementations tend to use T-carrier configuration with up to 23 B channels and one D channel. The E-carrier configuration uses 30 B channels and is used in Australia and Europe.

ISDN BRI vs. PRI – Similarities

The underlying technologies are similar in both.

  • BONDING (Bandwidth On Demand Interoperability Group) — a set of ISDN protocols that allow users to use more than one ISDN B channel. This is also known as multilink, channel aggregation, or load balancing.
  • Multilink PPP — a method for splitting, recombining, and sequencing data across multiple links. This is not specific to ISDN and can be applied to other technologies.

ISDN BRI vs. PRI – Differences


PRI is a scaled version of BRI. PRI is a T1 circuit that gives users the ability to combine B channels to form a larger network.


ISDN PRI is faster than ISDN BRI due to the sheer difference in the number of channels. BRI has a maximum speed of 128 kbps. PRI can be adjusted for speeds up to 2.94 Mbps. In the US, the available speed is usually between 1-1.5 Mbps.


BRI is used in many countries and is typically installed in residential areas or small businesses.  PRI is ideal for offering connectivity to medium and large enterprises. It can also function as a small PBX in the overall scheme of things.  Therefore, PRI is considered an industrial-level ISDN technology, and BRI is limited in its ability to scale up and handle large traffic, making it ideal for smaller setups.

Why is ISDN being switched off?

While the infrastructure of ISDN has been significantly upgraded since its inception in 1986, the network has remained relatively unchanged and is now a little outdated. In particular, broadband internet connection speeds are a lot faster than ISDN, and ISDN can no longer compete. In many states, it is already impossible to order new ISDN circuits. AT&T and Verizon have been pushing up line rental charges for some time for existing BRI customers. In 2017, Sprint switched off its Long Distance ISDN network, and Verizon is serving only legacy customers.  ISDN is set to be switched off completely over the next five years.

Contact CarrierBid for a free telecom consultation to switch from ISDN to other solutions that can better meet your needs.

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