Integrated Services Digital Network (ISDN)
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. 
Purpose and Role: ISDN was designed to move outdated analog telecommunication networks to digital. It allowed voice and data services to be delivered over the same lines. It also provided a single interface for hooking up a fax machine, a telephone, and a computer to the network.
Components: There are two main types of ISDN service:
- Basic Rate Interface (BRI): This is for home and small enterprise use. It consists of two 64 Kbps 'bearer' (B) channels and one 16 Kbps 'delta' (D) channel for control information.
- Primary Rate Interface (PRI): This is for larger applications. It consists of 23 B channels (30 in Europe) and one D channel used for control information, all running at 64 Kbps.
Importance: Before the advent of broadband internet, ISDN was important in offering high-speed data communications. It played a significant role in the evolution of the internet and networking technology.
Benefits: ISDN allowed both voice and data services to be handled digitally, providing better voice quality than an analog phone. It could also support a range of network services like call forwarding and hold. Plus, multiple devices could be used simultaneously with the same ISDN line.
Pros and Cons:
- Pros: Better voice quality, support for a range of services, simultaneous use of services, and faster than traditional modems.
- Cons: Higher cost, complex installation and setup, and has been largely superseded by DSL and other modern broadband technologies.
History: ISDN was first defined in 1988 by the CCITT organization, which is now the ITU-T (International Telecommunication Union Telecommunication Standardization Sector). While it was widely used for a time, especially in Europe, it has been largely replaced by broadband internet services.
Examples: ISDN has been used for voice calls, video conferencing, and high-speed internet. For instance, radio stations used ISDN to link to remote studios. However, with the rise of more modern, faster internet technologies like DSL and fiber-optic broadband, use of ISDN has dwindled.
- Defining Integrated Services Digital Network (ISDN) Lifewirw