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What is ISDN?

ISDN, which stands for Integrated Services Digital Network, is a set of communication standards for the simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network (PSTN). ISDN was developed to provide a more efficient and higher-quality alternative to traditional analog telephone systems.

Key features of ISDN


Digital Transmission

Unlike analog telephone lines that transmit voice signals as analog electrical waves, ISDN transmits information in a digital format, using binary code.

B Channels

ISDN lines consist of two types of channels: B (Bearer) channels and D (Data) channels. B channels are used for carrying voice and data, while D channels are used for signaling and control information.

Channel Capacity

B channels have a capacity of 64 Kbps (kilobits per second), and ISDN lines can have multiple B channels for concurrent voice or data transmission.

Dial-up and Permanent Connections

ISDN supports both dial-up connections, where users initiate a connection when needed, and permanent connections, which are always active.

Different Configurations

ISDN can be configured in various ways, such as Basic Rate Interface (BRI), which includes two B channels and one D channel, and Primary Rate Interface (PRI), which provides multiple B and D channels for higher capacity.

Switched and Permanent Virtual Circuits

ISDN allows the establishment of switched virtual circuits (SVCs) for on-demand connections and permanent virtual circuits (PVCs) for continuous, dedicated connections.


ISDN supports a range of applications, including voice calls, videoconferencing, and data transfer, making it a versatile solution for integrated communication services.

ISDN is due to be switched off in 2025. Read our handy ISDN switch off guide to see what this means to you. 

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