Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network. It was first defined in 1988 in the CCITT red book. ISDN is a circuit-switched telephone network system, which also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in better voice quality than an analog phone can provide.
ISDN provides two types of channels:
- Bearer Channels (B channels): B channels are used to carry voice, video, and data. Each B channel has a data rate of 64 kbps.
- Data Channels (D channels): D channels are used to carry signaling information. Each D channel has a data rate of 16 kbps or 64 kbps.
There are two types of ISDN interfaces:
- Basic Rate Interface (BRI): BRI provides two B channels and one D channel. BRI is intended for home and small business use.
- Primary Rate Interface (PRI): PRI provides 23 B channels and one D channel in North America and Japan, and 30 B channels and one D channel in Europe and the rest of the world. PRI is intended for large business use.
ISDN provides a variety of services, including:
- Voice: ISDN provides high-quality voice service.
- Video: ISDN can be used for video conferencing.
- Data: ISDN can be used for high-speed data transmission.
- Fax: ISDN can be used for high-speed fax transmission.
ISDN and the public switched telephone network (PSTN) are two different telephone network systems. The main difference between ISDN and the PSTN is the way that they transmit signals. ISDN transmits signals digitally, while the PSTN transmits signals in analog form. This makes ISDN more reliable and provides better voice quality than the PSTN.
ISDN was once a popular telephone network system, but it has been largely replaced by other technologies, such as DSL and cable modem. The decline of ISDN is due to a number of factors, including the high cost of ISDN hardware, the complexity of the ISDN protocol, and the rise of DSL and cable modem.