ISDNtelefoner

ISDNtelefoner, or ISDN phones, are telecommunication devices designed to operate over Integrated Services Digital Network (ISDN) lines. ISDN is a set of digital telecommunication standards that transmits both voice and data over the same lines. Unlike traditional analog phones, ISDN phones utilize digital signaling, offering higher call quality and the ability to handle multiple calls or data streams simultaneously on a single line.

The primary advantage of ISDN technology, and therefore ISDN phones, was its ability to support multiple channels. Basic Rate Interface (BRI) ISDN typically offered two 64 kbit/s bearer channels (B-channels) for voice or data, and one 16 kbit/s data channel (D-channel) for signaling and control. Primary Rate Interface (PRI) ISDN offered more channels, commonly used in business environments. This allowed for features such as simultaneous voice calls and internet access, or fax transmission.

ISDN phones themselves often featured more advanced capabilities than standard analog phones, including displays for caller ID, address books, and sometimes even the ability to send and receive short text messages. They connected to an ISDN Network Termination (NT) device, which then interfaced with the telecommunications provider's network. While ISDN was a significant advancement in its time, offering a clear upgrade from analog PSTN, it has largely been superseded by Voice over IP (VoIP) technology, which uses the internet protocol for voice communications and offers greater flexibility and cost-effectiveness. Consequently, ISDNtelefoner are now considered largely obsolete in most residential and many business applications, though they may still be found in niche or legacy systems.