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 (PSTN). It was first defined in 1988 by the International Telecommunication Union (ITU) in the ITU-T I-series Recommendations.

Overview

ISDN was designed to provide a higher quality of service and faster data transfer rates compared to the traditional analog telephone system. It integrates both voice and data on the same lines, which was a significant improvement over the earlier systems that required separate lines for voice and data.

Types of ISDN

There are two main types of ISDN services:

• Basic Rate Interface (BRI): This consists of two 64 kbps B-channels and one 16 kbps D-channel (2B+D). It is typically used for home and small enterprise applications.
• Primary Rate Interface (PRI): This consists of 23 B-channels and one 64 kbps D-channel (23B+D) in North America and Japan, and 30 B-channels and one 64 kbps D-channel (30B+D) in Europe and Australia. PRI is used for larger enterprise applications.

Components

ISDN requires several components to function:

• Terminal Equipment (TE): Devices such as telephones, computers, and fax machines that connect to the ISDN network.
• Network Termination (NT): Devices that connect the terminal equipment to the ISDN network. There are two types: NT1 and NT2.
• Terminal Adapter (TA): A device that allows non-ISDN equipment to connect to the ISDN network.

Protocols

ISDN uses several protocols to manage the communication between devices:

• LAPD (Link Access Procedure for the D-channel): Used for signaling and control.
• Q.931: Used for call setup and teardown.
• PPP (Point-to-Point Protocol): Used for data transmission over ISDN.

Applications

ISDN has been used in various applications, including:

• Video conferencing
• Broadband Internet access
• Telecommuting
• Remote education
• Telemedicine

Advantages

Some of the advantages of ISDN include:

• Higher data transfer rates compared to analog systems.
• Simultaneous transmission of voice and data.
• Improved voice quality.
• Faster call setup times.

Disadvantages

Despite its advantages, ISDN has some disadvantages:

• Higher cost compared to analog systems.
• Complexity in setup and configuration.
• Limited availability in some regions.

Decline and Legacy

With the advent of newer technologies such as DSL and fiber-optic networks, the use of ISDN has declined. However, it laid the groundwork for many modern digital communication technologies.

See also

• Public switched telephone network
• Digital Subscriber Line
• Fiber-optic communication
• Voice over IP
• Broadband