What Is ISDN?

Date First Published: 1st March 2022

Topic: Computer Networking

Subtopic: Network Standards

Article Type: Computer Terms & Definitions

Difficulty Level: 8/10

Learn more about what ISDN is in this article.

Short for Integrated Services Digital Network, ISDN is a set of communication standards that transmit data, video, voice, and other network services at the same time. It is a telecommunications technology that transmits digital data over standard phone lines and is a development of the plain old telephone service (POTS). They are used instead of traditional switched telephone network circuits because they can combine data and speech on exactly the same line. It was impossible for normal telephone lines to offer fast transmission over a single line before ISDN was introduced.

ISDN is a circuit-switched telephone network system that is capable of transferring all types of data over a single telephone line. Voice and data were no longer separated as they were in earlier technologies. ISDN additionally enables access to packet-switched networks.

ISDN is used with certain protocols, such as Q.931. In the OSI model, it acts as the network, data link, and physical layers. ISDN is really a suite of transmission services on the first, second, and third layers of the OSI model.

Types Of ISDN

Four different types of ISDN exist, which include:

• BRI (Basic Rate Interface) - Over a standard two-wire telephone line, an ISDN line can provide up to two 64 Kbit/s B channels and one 16 Kb/s D channel. The 16 Kbit/s channel, also known as the data channels is used for the purpose of protocol negotiation.
• PRI (Primary Rate Interface) - In a single E1 connection, this offers 30 bearer channels and two extra channels for a total data transfer rate of 2,048 Kb/s. This was a higher speed ISDN that was intended for use by businesses. It fully makes use of 23 parallel 64 Kbit/s bearer channels.
• N-ISDN - (Narrowband ISDN) - An attempt to replace the analogue telephone system with a digital one. N-ISDN uses a 64 Kbit/s channel as the basic unit of switching.
• B-ISDN - (Broadband ISDN) - The broadband transmission version of the ISDN. This is an advanced version of ISDN that was designed for running over fibre optic cables using ATM (Asynchronous Transfer Mode) switching technology in order to transmit hundreds of Mb/s of data in both download and upload. This type of ISDN was never in common use.

History

In 1988, ISDN was officially standardised. It became more popular in the 1990s as a faster alternative to the 56 Kb/s dial-up connection for internet access. The speed of ISDN was 128 Kb/s. When telecom companies moved from analogue to digital infrastructures, modern, long-distance networking and broadband internet technologies made it an outdated and no longer used technology. As of now, ISDN has been replaced by broadband internet access connections, such as WAN and cable modems.